bluuebunny/crossref_metadata_2025 huggingface dataset:
Glycine induces two distinct membrane currents in neonatal rat sympathetic preganglionic neurones in vitro.
Authors: Wu S Y , Miyazaki T , Dun N J
Published: December 2014

1. The effects of glycine (Gly) on neonatal (12‐ to 16‐day‐old) rat sympathetic preganglionic neurones (SPNs) in transverse (500 microns) thoracolumbar spinal cord slices were studied by whole‐cell patch‐clamp techniques. 2. Gly elicited three types of membrane currents when applied to SPNs by pressure ejection (100 mM; 20‐180 ms pulse duration): (1) an outward current (20/94 cells); (2) an inward current (30/94); and (3) a biphasic response (44/94) consisting of an outward followed by an inward current. 3. The Gly‐induced outward current (IGly,(out)) had a mean reversal potential of ‐67 mV, was reversed in a low (5.7 mM) chloride Krebs solution, and was reversibly eliminated by strychnine (0.1‐1 microM). 4. The Gly‐induced inward current (IGly,(in)) had a mean reversal potential of ‐41 mV, was reduced in a Na(+)‐free and increased in a high (15 mM) K+ solution; strychnine at the high concentration of 1 microM reduced the response by an average of 53%. 5. The electrophysiological and pharmacological characteristics of the biphasic response suggest that it was a combined response of outward and inward currents. 6. The results show that Gly elicits two distinct membrane currents, a Cl(‐)‐dependent outward current and a cationic inward current, which are mediated by strychnine‐sensitive and strychnine‐resistant Gly receptors. Functionally, activation of both types of Gly receptors reduces neuronal excitability and attenuates synaptic transmission.
Electrophysiological and metabolic effects of a convulsant barbiturate on dissociated mouse primary sensory neurons.
Authors: Pearce R J , Duchen M R
Published: December 2014

1. The convulsant barbiturate 5‐(2‐cyclohexylidene‐ethyl)‐5‐ethyl barbituric acid (CHEB) depolarizes dorsal root ganglion (DRG) neurons. We have applied microfluorimetric and whole‐cell patch clamp techniques to investigate the mechanisms underlying this response in freshly dissociated mouse DRG cells. 2. Application of CHEB (2‐200 microM) raised cytosolic calcium concentration ([Ca2+]i) rapidly and reversibly in 55% of eighty‐three neurons tested. This population did not correlate with other classifications of sensory neurons based on either cell size or the expression of membrane currents. 3. The response was dependent on external calcium and was reduced by 81 +/‐ 22% by Ruthenium Red. A rise in [Ca2+]i was still seen with the membrane potential clamped at ‐70 mV, excluding membrane depolarization and activation of voltage‐dependent Ca2+ channels as the principal mechanism for the response. 4. The rise in [Ca2+]i was associated with an increase in membrane conductance and a current, ICHEB, which was inward at ‐70 mV. Both the rise in [Ca2+]i and the current showed ‘run‐down’ under whole‐cell recording conditions. When K+ conductances were blocked, the reversal potential of ICHEB was close to 0 mV. This was independent of the Cl‐ reversal potential, suggesting that ICHEB is carried as a non‐specific cation current. 5. In contrast to the change in [Ca2+]i, ICHEB was not dependent on external Ca2+ and the current was still seen when [Ca2+]i as strongly buffered by the pipette filling solution. These data suggest that CHEB opens a non‐selective cation channel permeant to Ca2+, raising [Ca2+]i and further depolarizing the cell membrane potential. The exact nature of this conductance remains unknown. These actions could readily account for the convulsant actions of the drug, depolarizing neurons and increasing transmitter release. 6. It was also noted that CHEB increases autofluorescence derived from mitochondrial NAD(P)H. Further examination of this phenomenon using the dye rhodamine 123 to follow changes in mitochondrial potential (psi m) suggested that CHEB is a potent inhibitor of mitochondrial respiration, probably acting at complex I. These effects appeared to be quite distinct from the action of CHEB at the level of the plasma membrane.
Interneurones mediating presynaptic inhibition of group II muscle afferents in the cat spinal cord.
Authors: Jankowska E , Riddell J S
Published: December 2014

1. To investigate whether dorsal horn interneurones with input from group II muscle afferents induce depolarization of sensory fibres, simultaneous recordings were made from single interneurones in the sacral segments and from sacral dorsal root filaments using the spike‐triggered averaging technique. 2. The spike potentials of eighteen out of thirty‐eight interneurones tested were followed by dorsal root potentials (DRPs). The DRPs occurred at latencies of 2 and 6‐8 ms. Interneurones evoking DRPs at latencies of up to 2 ms are considered likely to be last‐order interneurones in pathways of presynaptic inhibition, while those inducing DRPs at longer latencies are considered likely to be first‐order interneurones. The former were activated by peripheral afferents with somewhat longer latencies than the latter. However, all interneurones were co‐activated by group II muscle and cutaneous afferents, indicating that the depolarization of group II muscle afferents, which these afferents induce, may be mediated by the same interneurones. 3. DRPs evoked by electrical stimulation of peripheral nerves were recorded from both sacral and midlumbar dorsal root filaments. The amplitudes of these DRPs were closely related to the potency with which group II afferents of various nerves activate dorsal horn interneurones in the sacral and midlumbar segments and group II afferents contributed to them more effectively than group I afferents. The second stimulus in a train was more effective than the first, while a third stimulus had little additional effect, indicating that the interneurones involved are relatively easily activated. 4. Intraspinal stimuli applied within the dorsal horn, at the sites where the largest field potentials of group II origin were recorded, evoked distinct DRPs. However, the location of the first‐ and last‐order interneurones in pathways of primary afferent depolarization (PAD) could not be differentiated by this approach because the same stimuli induced positive potentials, which masked the onset of DRPs and precluded localization of the sites from which DRPs might be evoked monosynaptically.
A micropuncture study of renal tubular lithium reabsorption in sodium‐depleted rats.
Authors: Walter S J , Sampson B , Shirley D G
Published: December 2014

1. The marked reduction in fractional lithium excretion (FELi) which accompanies chronic sodium depletion was investigated using free‐flow micropuncture in anaesthetized rats which had been maintained in a sodium‐depleted state for 8‐10 days. 2. Compared with previous values in sodium‐replete rats, sodium depletion was associated with small reductions in total and superficial nephron glomerular filtration rate and enhanced fractional reabsorption of water, sodium and lithium in the proximal convoluted tubule. 3. In untreated (sodium‐depleted) rats, fractional deliveries of lithium (FDLi) to the late proximal convoluted tubule, early distal tubule and late distal tubule were 0.41 +/‐ 0.02, 0.20 +/‐ 0.01 and 0.18 +/‐ 0.02 (means +/‐ S.E.M.), respectively. Fractional lithium excretion (0.08 +/‐ 0.01) was significantly lower than late distal FDLi (P < 0.001). 4. Treatment with amiloride did not affect segmental lithium handling up to the late distal tubule. Frusemide had no effect on lithium reabsorption in the proximal convoluted tubule, but early distal FDLi (0.30 +/‐ 0.01) was raised compared with the untreated group (P < 0.001). Both diuretics eliminated the difference between late distal FDLi and FELi, respective values being 0.17 +/‐ 0.02 and 0.15 +/‐ 0.01 (amiloride‐treated rats) and 0.31 +/‐ 0.02 and 0.34 +/‐ 0.02 (frusemide‐treated rats). 5. These data indicate that part of the reduction in FELi in chronic sodium depletion is due to enhanced fractional fluid (and lithium) reabsorption in the proximal convoluted tubule. In addition, however, they provide direct evidence for amiloride‐sensitive lithium reabsorption in the collecting ducts.(ABSTRACT TRUNCATED AT 250 WORDS)
Shifts of thermoeffector thresholds in heat‐acclimated rats.
Authors: Shido O , Sakurada S , Sugimoto N , Nagasaka T
Published: December 2014

1. Heat‐acclimated (HA) rats, kept under a 12:12 h light‐dark regime, were subjected to an ambient temperature (Ta) of 33 degrees C for 5 h in the last half of the dark phase for 3 weeks. Control rats were kept under a 12:12 h light‐dark regime at a constant Ta of 24 degrees C. 2. After the acclimation period, the rats were then placed in a metabolic chamber at a Ta of 26.5 degrees C, and body core temperature was gradually increased and decreased using an intravenous thermode. Thermoeffector thresholds were determined by the hypothalamic temperature (T(hy)) at the onset of warm‐induced tail skin vasodilatation and cold‐induced thermogenesis measured by oxygen consumption. 3. Each rat was subjected to the experiment twice, once in the first half and once in the last half of the dark phase, on different days in random order. 4. In HA rats, T(hy) at the onset of both skin vasodilatation and thermogenesis were significantly lower in the last half of the dark phase compared with the first half. In control rats, however, there were no such differences between the two halves. 5. The results suggest that in rats acclimated to daily heat exposure, thermoeffector thresholds shift to lower temperatures only during the period of day when the rats had previously been exposed to heat.
Pivotal role of phosphate chain length in vasoconstrictor versus vasodilator actions of adenine dinucleotides in rat mesenteric arteries.
Authors: Ralevic V , Hoyle C H , Burnstock G
Published: December 2014

1. The isolated perfused rat mesenteric arterial bed was used to examine the activity of the adenine dinucleotides: beta‐nicotinamide adenine dinucleotide (NAD); beta‐nicotinamide adenine dinucleotide phosphate (NADP); flavin adenine dinucleotide (FAD); and of the alpha,omega‐diadenosine polyphosphates: adenylyl adenosine (AP1A); P1,P2‐diadenosine pyrophosphate (AP2A); P1,P3‐diadenosine triphosphate (AP3A); P1,P4‐diadenosine tetraphosphate (AP4A); P1,P5‐diadenosine pentaphosphate (AP5A); P1,P6‐diadenosine hexaphosphate (AP6A). Responses were compared with those of ADP, ATP, 2‐methylthio‐ATP (2‐meSATP) and alpha,beta‐methylene ATP (alpha,beta‐meATP). 2. In basal tone preparations mono‐ and dinucleotides elicited vasoconstriction with the order of potency: alpha,beta‐meATP > or = AP5A > or = AP6A > or = AP4A > or = 2‐meSATP >> ATP >> ADP. The dinucleotides NAD, NADP, FAD, AP1A, AP2A and AP3A had no effect. 3. The P2X‐purinoceptor antagonist pyridoxalphosphate‐6‐azophenyl‐2',4'‐disulphonic acid (30 microM) virtually abolished vasoconstrictor responses to AP4A, AP5A and AP6A. 4. Auto‐ and cross‐desensitization of vasoconstrictor responses to AP4A, AP5A, AP6A, ATP and alpha,beta‐meATP were observed. 5. In raised tone preparations nucleotides elicited endothelium‐dependent vasodilatation with the order of potency: 2‐meSATP = ADP > ATP > AP3A > AP2A > AP1A = NADP = FAD > NAD. The nucleotides AP4A, AP5A, AP6A and alpha,beta‐meATP had no vasodilator effects. 6. It is concluded that the alpha,omega‐adenine dinucleotides AP4A, AP5A and AP6A elicit vasoconstriction, but not vasodilatation, in the rat mesenteric arterial bed via P2x‐purinoceptors. In contrast, the dinucleotides NADP, FAD, AP1A, AP2A and AP3A elicit vasodilatation, but not vasoconstriction, via endothelial P2Y‐purinoceptors. 7. It is suggested that there is a crucial relationship between the structure of the alpha,omega‐diadenosine polyphosphates and their activity at P2X‐ and P2Y‐purinoceptors with a pivotal role played by the polyphosphate chain. Molecules with four or more phosphates are vasoconstrictors, while those with three or less phosphates are vasodilators.
Relative degree of stimulation‐evoked glycogen degradation in muscle fibres of different type in rat gastrocnemius.
Authors: Kernell D , Lind A , van Diemen A B , De Haan A
Published: December 2014

1. The relative degree of glycogen degradation, caused in different fibre types by supramaximal electrical activation of the muscle nerve, was investigated in m. gastrocnemius medialis of young adult rats under general pentobarbitone anaesthesia. Four different protocols of intermittent maximal tetanic activation were used, each lasting 6 s (33% duty cycle; fast and slow isovelocity concentric (shortening) contractions, brief‐ and long‐burst isometric contractions; 6 rats per group). All contractions were evoked under ischaemic conditions. 2. Work output finally dropped to 29% of the initial value for the fast concentric and to 87% for the slow concentric contractions. In isometric protocols evoked by the same stimulation patterns, the force x time area rose to 110% for brief‐burst contractions and dropped to 95% for the long‐burst contractions. 3. Following the physiological procedures, the experimental muscle and its contralateral control were removed and prepared for histochemical analysis. Serial sections were stained for glycogen (periodic acid‐Schiff (PAS) method) and myofibrillar ATPase (mATPase), the latter reactions being used for classifying the fibres as types I, IIA, IIBd and IIBm. 4. For deep ‘red’ regions of non‐stimulated contralateral control muscles the optical density of PAS staining was ranked between fibre types such that I < IIA < IIBd < IIBm. In superficial ‘white’ regions of the same muscles, no significant difference in PAS staining density was found between IIBd and IIBm fibres (types I and IIA not present). 5. All contractile protocols produced a significant glycogen degradation in IIBm fibres, and the fast concentric activation procedure was associated with a significant decline of PAS staining in all fibre types. For all activation protocols, the relative degree of glycogen degradation within a given region was ranked such that IIBm > IIBd > IIA > I. For IIBm vs. IIBd fibres, the differences in relative degradation were greater and more consistently significant for superficial white regions than in the deeper red muscle portions. 6. The results are discussed in relation to glycogen degradation measurements in studies of motor unit recruitment. Furthermore, the results from red vs. white muscle regions underline that fibres of seemingly the same mATPase type may differ considerably in other properties.
Effects of lowered cytoplasmic calcium concentration and light on the responses of salamander rod photoreceptors.
Authors: Matthews H R
Published: December 2014

1. In order to study the interactions between cytoplasmic calcium concentration ([Ca2+]i) and light in modulating the responses of rod photoreceptors, [Ca2+]i was held at different levels by manipulating Ca2+ fluxes across the outer segment membrane. 2. If [Ca2+]i was reduced by the removal of external Ca2+ in the continued presence of Na+, and then held near this reduced level by exposure to 0 Ca(2+)‐0 Na+ solution, the onset of the recovery phase of the response to a bright flash delivered just before the return to Ringer solution was accelerated, much as is the case during light adaptation, provided that precautions were taken to minimize Na+ influx. 3. If the rod was first allowed to adapt to steady light, [Ca2+]i held near the appropriate light‐adapted level by superfusion with 0 Ca(2+)‐0 Mg(2+)‐0 Na+ solution and the light extinguished, the onset of the recovery phase of the bright flash response varied with the original background intensity in the same way as in the continued presence of steady light. These results indicate that reduction of [Ca2+]i is sufficient to induce this manifestation of light adaptation in darkness. 4. When [Ca2+]i was held at a reduced level in darkness, not only was the sensitivity to dim flashes reduced, but the response rising phase was also delayed and its amplitude increased supralinearly with flash intensity, neither of which changes is seen during light adaptation. However, similar changes in response kinetics resulted when [Ca2+]i was held near its normal dark level and the phosphodiesterase was partially inhibited by 3‐isobuty‐1‐methylxanthine (IBMX), suggesting that they arose indirectly from an elevated cyclic GMP concentration rather than from a direct effect of Ca2+. 5. If [Ca2+]i was held near the normal dark level and bright steady light presented, the circulating current was completely suppressed. Partial inhibition of the phosphodiesterase by superfusion with 0 Ca(2+)‐0 Na+ solution including IBMX resulted in restoration of the circulating current. Dim flash responses recorded under these conditions exhibited kinetics similar to those recorded in 0 Ca(2+)‐0 Na+ solution in darkness, in contrast to the response acceleration seen when [Ca2+]i was held near the appropriate light‐adapted level. These results indicate that the kinetics of the flash response depend on [Ca2+]i rather than on the steady light intensity.
The role of glutamate and GABA receptors in the generation of dorsal root reflexes by acute arthritis in the anaesthetized rat.
Authors: Rees H , Sluka K A , Westlund K N , Willis W D
Published: December 2014

1. In rats anaesthetized with pentobarbitone sodium, a unilateral acute arthritis was produced by the injection of kaolin and carrageenan into one knee‐joint cavity. Four hours after injection, the medial articular nerve (MAN) was sectioned distally and recordings obtained from the proximal stump of the nerve. 2. Centrifugally conducted action potentials were recorded from the cut MAN following the development of arthritis. Acute dorsal rhizotomy, but not sympathectomy, prevented the action potentials, and so it is concluded that the action potentials represent dorsal root reflexes. 3. Central administration of either the GABAA receptor antagonist, bicuculline, or the non‐NMDA receptor antagonist, CNQX, also prevented dorsal root reflexes in the MAN. 4. Neither the GABAB receptor antagonist, CGP35348, nor the NMDA receptor antagonist, AP7, altered the dorsal root reflexes in the MAN. 5. It is concluded that arthritis causes excess primary afferent depolarization in the dorsal horn of the spinal cord leading to dorsal root reflexes. It is proposed that these dorsal root reflexes contribute to the inflammation.
Vagal control of nitric oxide and vasoactive intestinal polypeptide release in the regulation of gastric relaxation in rat.
Authors: Takahashi T , Owyang C
Published: December 2014

1. Gastric motility and neurotransmitter release in response to vagal stimulation were studied using a vascularly isolated perfused rat stomach. Gastric motor responses were recorded by a strain gauge force transducer implanted on the proximal stomach. 2. Electrical stimulation of vagal trunk (0.5‐20 Hz) produced a triphasic response which was composed of a rapid transient relaxation (first phase) followed by a phasic contraction (second phase) and a delayed prolonged relaxation (third phase). Maximum responses of the first, second and third phase were observed at 2.5, 5 and 10 Hz, respectively. Intra‐arterial infusion of tetrodotoxin (0.1 microM) or hexamethonium (100 microM) completely abolished the triphasic response. 3. The nitric oxide (NO) biosynthesis inhibitor NG‐nitro‐L‐arginine (L‐NNA; 100 microM) significantly antagonized the rapid relaxation but had no effect on the delayed relaxation, while vasoactive intestinal polypeptide (VIP) antagonist (1 microM) significantly reduced the delayed relaxation without affecting the rapid relaxation. 4. In response to vagal stimulation, NO production ([3H]citrulline formation in gastric tissue preloaded with [3H]arginine) was maximum at 2.5 Hz, whereas VIP release into the venous effluent was largest at 10 Hz. Hexamethonium abolished vagal‐stimulated NO production and VIP release. L‐NNA had no effect on VIP release in response to vagal stimulation. 5. The nicotinic receptor agonist 1,1‐dimethyl‐4‐phenylpiperizinium (DMPP; 100 microM) also caused a triphasic response similar to that observed with vagal stimulation and produced a significant increase in VIP and NO formation. DMPP‐evoked VIP release was not affected by L‐NNA. Similarly, DMPP‐evoked NO production was not antagonized by VIP antagonist. 6. These results suggest that vagus nerve stimulation evokes NO and VIP release via nicotinic synapses which cause different modes of relaxation of the stomach. There is no interaction between NO and VIP release in response to vagal stimulation.
Characterization of the G protein coupling of a somatostatin receptor to the K+ATP channel in insulin‐secreting mammalian HIT and RIN cell lines.
Authors: Ribalet B , Eddlestone G T
Published: December 2014

1. The G protein‐mediated coupling of a somatostatin (somatotropin‐releasing inhibitory factor; SRIF) receptor to the ATP‐dependent K+ channel (K+ATP channel) has been studied in insulin‐secreting cells using the patch clamp technique. 2. In excised outside‐out patches, the concentration‐dependent stimulation of the K+ATP channel by SRIF was biphasic. Stimulation reached a maximum at 15 nM (EC50 = 5.5 nM), then decayed to a minimum at 50 nM and returned to maximum stimulation at 500 nM. 3. In cell‐attached patches, bath‐applied SRIF caused K+ATP channel stimulation in most experiments. In a few cases, however, SRIF suppressed channel activity, a response that was reversed by addition of dibutyryl cyclic AMP (DBcAMP). Channel stimulation by SRIF or by DBcAMP did not occur in the presence of glucose. 4. In excised inside‐out patches, the alpha‐subunits of Gi or G(o)‐type G proteins stimulated the K+ATP channel (EC50 = 29 and 42 pM, respectively). The K+ATP channel stimulation by alpha i‐ or alpha o‐subunits had no effect on the concentration‐dependent inhibition by ATP. 5. In excised inside‐out patches, K+ATP channel activity was reduced by inhibitors of protein kinase C (PKC) and stimulated by a PKC activator. The stimulatory effect of PKC was unaffected by the presence of pertussis toxin, but stimulation by exogenous alpha‐subunits of the G protein Gi or G(o) was prevented by PKC inhibitors. 6. From these data we deduce that SRIF can affect K+ATP channel activity directly via a membrane‐delimited pathway or indirectly via a pathway requiring diffusible messengers. In the former case, alpha i/alpha o may either enhance PLC activity, stimulating PKC and thus inducing K+ATP channel phosphorylation with consequent increase of activity, or channel phosphorylation by PKC may facilitate a direct stimulation of the channel by alpha i/alpha o. In the latter case, an alpha i/alpha o‐induced fall in cAMP contributes to reduced PKA‐mediated phosphorylation and suppression of channel activity.
The suppression of Ca(2+)‐ and voltage‐dependent outward K+ current during mAChR activation in rat adrenal chromaffin cells.
Authors: Herrington J , Solaro C R , Neely A , Lingle C J
Published: December 2014

1. The mechanism by which muscarine, ionomycin or caffeine results in suppression of Ca(2+)‐ and voltage‐dependent outward current in rat adrenal chromaffin cells was evaluated using both whole‐cell voltage clamp and single channel recording. 2. The whole‐cell current activated following the elevation of the cytosolic calcium concentration ([Ca2+]i) by muscarine inactivates with a time course comparable to that of single Ca(2+)‐ and voltage‐dependent potassium (BK) channels. 3. The whole‐cell inactivating current is pharmacologically similar to BK current. 4. The voltage dependence of inactivation and rate of recovery from inactivation are qualitatively similar for both whole‐cell current and ensemble averages of single BK channels. Furthermore, changes in the rate of whole‐cell current inactivation track expected changes in submembrane [Ca2+]. 5. The suppression of outward current can be accounted for solely by inactivation of BK channels and does not depend on the means by which [Ca2+]i is elevated. 6. Muscarinic acetylcholine receptor (mAChR) activation, changes in holding potential (‐50 to ‐20 mV), and step depolarizations of different amplitude and duration were tested for their ability to elevate [Ca2+]i and thereby regulate the availability of BK current for activation. 7. Following muscarine‐induced elevation of [Ca2+]i at holding potentials positive to ‐40 mV, the availability of BK current for activation was typically reduced by more than 50%. 8. Holding potentials in the range of ‐50 to ‐20 mV produced only slight alterations in the availability of BK current for activation. 9. Step depolarizations that cause maximal rates of Ca2+ influx (0 to +10 mV) must exceed 200 ms to reduce the availability of BK current by approximately 50%. 10. The results show that the muscarine‐induced elevation of [Ca2+]i produces a profound reduction in the availability of BK channels for activation at membrane potentials likely to be physiologically meaningful. Although depolarization‐ induced Ca2+ influx can inactivate BK current, we propose that short duration depolarizations that occur during normal electrical activity will not significantly alter BK channel availability.
Ca(2+)‐permeable AMPA and NMDA receptor channels in basket cells of rat hippocampal dentate gyrus.
Authors: Koh D S , Geiger J R , Jonas P , Sakmann B
Published: December 2014

1. Glutamate receptor (GluR) channels were studied in basket cells in the dentate gyrus of rat hippocampal slices. Basket cells were identified by their location, dendritic morphology and high frequency of action potentials generated during sustained current injection. 2. Dual‐component currents were activated by fast application of glutamate to outside‐out membrane patches isolated from basket cell somata (10 microM glycine, no external Mg2+). The fast component was selectively blocked by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), the slow component by D‐2‐amino‐5‐phosphonopentanoic acid (D‐AP5). This suggests that the two components were mediated by alpha‐amino‐3‐ hydroxy‐5‐methyl‐4‐isoxazolepropionate receptor (AMPAR)/kainate receptor and N‐methyl‐D‐aspartate receptor (NMDAR) channels, respectively. The mean ratio of the peak current of the NMDAR component to that of the AMPAR/kainate receptor component was 0.22 (1 ms pulses of 10 mM glutamate). 3. The AMPAR/kainate receptor component, which was studied in isolation in the presence of D‐AP5, was identified as AMPAR mediated on the basis of the preferential activation by AMPA as compared with kainate, the weak desensitization of kainate‐activated currents, the cross‐desensitization between AMPA and kainate, and the reduction of desensitization by cyclothiazide. 4. Deactivation of basket cell AMPARs following 1 ms pulses of glutamate occurred with a time constant (tau) of 1.2 +/‐ 0.1 ms (mean +/‐ S.E.M.). During 100 ms glutamate pulses AMPARs desensitized with a tau of 3.7 +/‐ 0.2ms. 5. The peak current‐voltage (I‐V) relation of AMPAR‐mediated currents in Na(+)‐rich extracellular solution showed a reversal potential of ‐4.0 +/‐ 2.6 mV and was characterized by a a doubly rectifying shape. The conductance of single AMPAR channels was estimated as 22.6 +/‐ 1.6 pS using non‐stationary fluctuation analysis. AMPARs expressed in hippocampal basket cells were highly Ca2+ permeable (PCa/PK = 1.79). 6. NMDARs in hippocampal basket cells were studied in isolation in the presence of CNQX. Deactivation of NMDARs activated by glutamate pulses occurred bi‐exponentially with mean tau values of 266 +/‐ 23 ms (76%) and 2620 +/‐ 383 ms (24%). 7. The peak I‐V relation of the NMDAR‐mediated component in Na(+)‐rich extracellular solution showed a reversal potential of 1.5 +/‐ 0.6 mV and a region of negative slope at negative membrane potentials in the presence of external Mg2+, due to voltage‐dependent block by these ions. The conductance of single NMDAR channels in the main open state was 50.2 +/‐ 1.8 pS.(ABSTRACT TRUNCATED AT 400 WORDS)
Suppression of calcium release by calcium or procaine in voltage clamped rat skeletal muscle fibres.
Authors: García J , Schneider M F
Published: December 2014

1. Calcium transients were measured in fast‐twitch rat skeletal muscle fibres stretched to 3.7‐4.0 microns per sarcomere, and voltage clamped at a holding potential of ‐80 mV using the double‐seal Vaseline gap technique. Resting calcium was monitored with fura‐2 and the calcium transients were measured with antipyrylazo III. The rate of release of calcium from the sarcoplasmic reticulum was calculated from the calcium transient records. The temperature was 14‐17 degrees C. 2. The steady‐state calcium dependence of inactivation of release was studied with a two‐pulse protocol in which 200 ms prepulses of different amplitudes elevated the internal calcium concentration to various levels. The inactivation of release was then measured in the test pulse that followed the prepulses. The calcium concentration at which the inactivation of release are half‐maximal was approximately 0.22 microM, the average number of bound calcium ions needed to cause inactivation was about three per release channel and the amount of release that could be inactivated was, on average, 2.48 times the steady level of release during the test pulses. 3. Procaine (0.3mM) reversibly decreased the amplitude and the rate of rise of the calcium transient. Both the peak and the steady level of release were decreased by about 50%. The shape of the release waveform was not modified.
Effect of chronic hypoxaemia from birth upon chemosensitivity in the adult rat carotid body in vitro.
Authors: Landauer R C , Pepper D R , Kumar P
Published: December 2014

1. The effect of chronic hypoxaemia upon in vitro carotid body chemosensitivity was observed in eight rats > 5 weeks of age born and reared in 12% oxygen. Comparisons were made with eight age‐matched normoxic rats. 2. Single exponential functions with offset were fitted to the normalized (percentage of maximum) discharge responses to ramp decreases in PO2 at three steady levels of PCO2. CO2 sensitivity was derived from these functions. 3. Increasing hypercapnia increased the horizontal asymptote of the exponential functions in the normoxic (0.15 +/‐ 0.03% discharge per mmHg PCO2; P < 0.001) and chronically hypoxic (0.13 +/‐ 0.04% discharge per mmHg PCO2; P < 0.005) animals but was without effect upon the rate constants in both groups (‐0.04 +/‐ 0.18 mmHg PO2 per mmHg PCO2, P > 0.50 and 0.63 +/‐ 0.48 mmHg PO2 per mmHg PCO2, P > 0.20, respectively). Rate constants were greater in the chronically hypoxic animals (P < 0.05) compared with the normoxic animals. 4. CO2 chemosensitivity increased with decreasing PO2 in normoxic (P < 0.05) but not in chronically hypoxic (P > 0.50) rats. 5. Our results show that chronic hypoxaemia from birth attenuates the maturation of CO2‐O2 interaction at the carotid body.
Coincidence of early glucose‐induced depolarization with lowering of cytoplasmic Ca2+ in mouse pancreatic beta‐cells.
Authors: Chow R H , Lund P E , Löser S , Panten U , Gylfe E
Published: December 2014

1. The temporal relationship between the early glucose‐induced changes of membrane potential and cytoplasmic Ca2+ concentration ([Ca2+]i) was studied in insulin‐releasing pancreatic beta‐cells. 2. The mean resting membrane potential and [Ca2+]i were about ‐70 mV and 60 nM, respectively, in 3 mM glucose. 3. Elevating the glucose concentration to 8‐23 mM typically elicited a slow depolarization, which was paralleled by a lowering of [Ca2+]i. When the slow depolarization had reached a threshold of ‐55 to ‐40 mV, there was rapid further depolarization to a plateau with superimposed action potentials, and [Ca2+]i increased dramatically. 4. Imposing hyperpolarizations and depolarizations of 10 mV from a holding potential of ‐70 mV had no detectable effect on [Ca2+]i. Furthermore, glucose elevation elicited a decrease in [Ca2+]i even at a holding potential of ‐70 mV. 5. Step depolarizations induced [Ca2+]i transients, which decayed with time courses well fitted by double exponentials. The slower component became faster by a factor of about 4 upon elevation of glucose, suggesting involvement of ATP‐dependent Ca2+ sequestration or extrusion of [Ca2+]i. 6. Glucose stimulation increased the size and accelerated the recovery of carbachol‐triggered [Ca2+]i transients, and thapsigargin, an intracellular Ca(2+)‐ATPase inhibitor, counteracted the glucose‐induced lowering of [Ca2+]i, indicating that calcium transport into intracellular stores is involved in glucose‐induced lowering of [Ca2+]i. 7. The results support the notion that in beta‐cells, nutrient‐induced elevation of ATP leads initially to ATP‐dependent removal of Ca2+ from the cytoplasm, paralleled by a slow depolarization due to inhibition of ATP‐sensitive K+ channels. Only after depolarization has reached a threshold do action potentials occur, inducing a sharp elevation in [Ca2+]i.
Effect of vibration on antagonist muscle coactivation during progressive fatigue in humans.
Authors: Rothmuller C , Cafarelli E
Published: December 2014

1. Biceps femoris antagonist coactivation increases during progressive fatigue. Our purpose was to determine if the mechanism that increases coactivation during fatigue is susceptible to vibration. Vibration drives alpha‐motoneurons via the Ia loop, producing force without descending motor drive, and thus uncoupling antagonist and agonist activation. Evidence that vibration increases coactivation disproportionately from its ‘common drive’ would suggest the possibility that some of the effects of fatigue are mediated through a segmental reflex loop. 2. Ten male subjects performed repeated maximal voluntary isometric contractions (MVCs) of the knee extensors of one leg. Paired submaximal test contractions (50% of MVC), without visual feedback, were performed when MVC reached 85, 70 and then 50% of its initial value. Vibration was applied to the patellar tendon during one test contraction in each pair. 3. Vibration reduced test contraction force below control values. However, coactivation increased at the same rate in both conditions. Biceps femoris coactivation was greater during vibration, but did not change during fatigue in either condition. 4. Our observations suggest that agonist‐antagonist muscle pairs are controlled as a single motor unit pool by a common central drive. Vibrating the agonist increases antagonist coactivity, but does not alter the rate at which coactivation increases during fatigue. This supports the idea that agonist coactivation is controlled by a central mechanism.
Potassium currents in adult rat intracardiac neurones.
Authors: Xi‐Moy S X , Dun N J
Published: December 2014

1. Properties of K+ currents were studied in isolated adult rat parasympathetic intracardiac neurones with the use of single‐electrode voltage‐clamp techniques. 2. A hyperpolarization‐activated inward rectifier current was revealed when the membrane was clamped close to the resting level (‐60 mV). The slowly developing inward relaxation had a mean amplitude of 450 pA at ‐150 mV, an activation threshold of ‐60 to ‐70 mV and a relaxation time constant of 41 ms at ‐120 mV. The current was reversibly blocked by Cs+ (1 mM) and became smaller with reduced [K+]o and [Na+]o, indicating that this inward rectifier current probably is a time‐ and voltage‐dependent Na(+)‐K+ current. 3. Step depolarizations from the holding potential of ‐80 mV evoked a transient (< 100 ms at ‐40 mV) outward K+ current (IA) which was blocked by 4‐aminopyridine (4‐AP, 1 mM). The time constants for IA inactivation were 20 ms at ‐50 mV and 16 ms at ‐20 mV. The steady‐state activation and (removal of) inactivation curve showed a small overlap between ‐70 and ‐40 mV; the reversal potential of IA was close to EK. 4. Step hyperpolarizations from the depolarized potentials, i.e. ‐30 mV, revealed a slow inward relaxation associated with the deactivation of a time‐ and voltage‐dependent current. The inward relaxation became faster at more hyperpolarized potentials and reversed at ‐85 and ‐53 mV in 4.7 and 15 mM [K+]o. This current was blocked by muscarine (20 microM) and Ba2+ (1 mM) but not affected by Cs+ (1 mM); this current may correspond to the M‐current (IM). 5. Depolarization‐activated outward K+ currents were evoked by holding the membrane close to the resting potential in the presence of tetrodotoxin (TTX, 3 microM), 4‐AP (1 mM) and Ba2+ (1 mM). The amplitude of the outward relaxation and the tail current became smaller as the [K+]o was elevated. The outward tail current was reduced in a Ca(2+)‐free solution and the residual current was eliminated by the addition of tetraethylammonium (TEA, 10 mM); the reversal potential was shifted in a direction predicted by the Nernst equation. These findings suggest the presence of delayed rectifier K+ current and Ca(2+)‐activated K+ current. 6. Superfusion of TEA, Ba2+ and 4‐AP, but not Cs+, induced rhythmic discharges in some of the otherwise quiescent intracardiac neurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Hyperosmotic modulation of the cytosolic calcium concentration in a rat osteoblast‐like cell line.
Authors: Dascalu A , Oron Y , Nevo Z , Korenstein R
Published: December 2014

1. The effects of hyperosmotic stress on cytosolic calcium concentration ([Ca2+]i) were studied by ratio image analysis in single cells of an osteoblast‐like bone cell line (RCJ 1.20) loaded with fura‐2 AM. 2. The ratio (340 nm/380 nm) of steady‐state [Ca2+]i in resting osteoblasts kept in Hepes‐buffered medium was 0.82 +/‐ 0.04. A hyperosmotic stimulus (200 mosmol l‐1 sucrose) produced a [Ca2+]i transient with a peak ratio of 1.28 +/‐ 0.09, which decayed with an apparent half‐life (t1/2) of 42.7 +/‐ 2.6 s. 3. The hyperosmotically induced [Ca2+]i transients were insensitive to verapamil, diltiazem or nifedipine, which excludes the involvement of dihydropyridine‐sensitive Ca2+ channels in the process. Non‐specific Ca2+ channel blockers (Mn2+, Ni2+, La3+ or Gd3+) partially abolished the hyperosmotically induced [Ca2+]i elevation, indicating the contribution of extracellular Ca2+ influx. 4. A hyperosmotic stimulus applied in Ca(2+)‐free medium (0.5 mM EGTA) lowered the [Ca2+]i peak to a ratio of 0.96 +/‐ 0.08 (P < 0.001) compared with a Ca(2+)‐containing medium. This suggests that the [Ca2+]i increase is due to extracellular influx, as well as release from an intracellular Ca2+ pool. 5. Application of thapsigargin (0.5 microM), a specific inhibitor of endoplasmic reticulum Ca(2+)‐ATPase, in Ca(2+)‐free medium caused transient [Ca2+]i elevation to peak ratios of 1.33 +/‐ 0.09, and completely abolished the [Ca2+]i response to a hyperosmotic stimulus. This implies the existence of a thapsigargin‐sensitive intracellular pool of Ca2+ that is mobilized by hyperosmotic stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)
Functional expression of the tachykinin NK1 receptor by floor plate cells in the embryonic rat spinal cord and brainstem.
Authors: Heath M J , Lints T J , Lee C J , Dodd J
Published: December 2014

1. The floor plate is a ventral mid‐line structure that plays a pivotal role in the organization of the developing vertebrate central nervous system. Previous studies have demonstrated that the floor plate may provide signals that induce neuronal differentiation and guide axons; however, it is not known whether the floor plate can itself respond to signals that derive from surrounding tissue. 2. The peptide substance P is one of the first transmitters to be expressed in the developing spinal cord. To determine whether the floor plate may respond to substance P we have examined the expression of the principal substance P receptor (the tachykinin NK1 receptor) by floor plate cells of the rat embryonic spinal cord using immunocytochemistry, in situ hybridization and fura‐2 calcium imaging. 3. Immunocytochemistry demonstrated selective expression of the NK1 receptor by cells at the ventral mid‐line of the spinal cord. Double immunofluorescence labelling with the specific floor plate marker FP3 indicated that NK1 receptor expression is confined to cells in the lateral region of the floor plate. 4. In order to confirm the specificity of the NK1 receptor immunoreactivity we performed in situ hybridization histochemistry using antisense cRNA probes directed against the NK1 receptor. In situ hybridization demonstrated selective expression of NK1 receptor mRNA by floor plate cells. 5. The ontogeny of NK1 receptor protein and mRNA expression in the floor plate was defined. NK1 receptor expression occurred in a rostrocaudal progression that begins at embryonic day 10‐11 (E10‐E11) and is complete by E12‐E14. The restriction of NK1 receptor expression to the lateral part of the floor plate was conserved throughout embryonic development. 6. NK1 receptor signalling was assessed by monitoring substance P‐evoked changes in the intracellular concentration of calcium ions ([Ca2+]i) of acutely dissociated cells from the floor plate region. Application of substance P (5 nM) elevated [Ca2+]i in 10% of cells examined. 7. Selective neurokinin agonists were used to identify the receptor subtype involved in the substance P‐evoked elevation of [Ca2+]i. Acetyl‐[Arg6,Sar9,Met(O2)11]‐substance P(6‐11) (5 nM) and [Sar9,Met(O2)11]‐substance P (5 nM), two highly selective NK1 receptor agonists, both elevated [Ca2+]i in floor plate cells that responded to substance P. [beta‐Ala8]‐neurokinin A(4‐10) (50 nM) and senktide (50 nM), selective agonists respectively of NK2 and NK3 receptors, had no effect on [Ca2+]i.
Burst kinetics of single NMDA receptor currents in cell‐attached patches from rat brain cortical neurons in culture.
Authors: Kleckner N W , Pallotta B S
Published: December 2014

1. The patch‐clamp technique was used to record single‐channel currents from cell‐attached patches on rat brain cortical neurons in culture. The composition of the open and shut intervals during bursts of openings was studied in N‐methyl‐D‐aspartate (NMDA) receptors exposed to 1 microM NMDA and 10 microM glycine at a membrane potential of ‐70 mV. 2. Open interval histograms were constructed for openings at each position (first, second, third, etc.) during all bursts. Distributions from openings two to five were fitted with similar (two or three) exponential components. The first opening from all bursts tended to be of shorter duration than the other openings. 3. Bursts were sorted according to the number of openings they contained and duration histograms were obtained for the openings at each position (one to five) during bursts of up to five openings. For bursts containing two or more openings, the distribution of open durations obtained at a given position were similar to each other regardless of the number of openings in the burst. 4. In bursts of two or more openings (up to five), duration histograms from the openings at each position in the burst were fitted with two or three exponential components that were similar for each opening. Bursts consisting of a single opening had a different distribution, having a relatively larger component of short duration. 5. Shut intervals during bursts were described by two exponential components with average time constants (and relative areas) (means +/‐ S.E.M.) of 0.06 +/‐ 0.01 ms (0.59 +/‐ 0.02) and 0.64 +/‐ 0.02 ms (0.41 +/‐ 0.02). Their distribution was independent of the numbers of openings in the bursts, their position within the burst, and the types of openings (long or short duration) contained within the burst. 6. These results suggest that each opening in bursts of two or more openings is kinetically similar to every other opening regardless of burst length. Analogously, each shut period during a burst was similar to every other. A kinetic model with three open and four closed intraburst states is shown to be consistent with these results for bursts of two or more openings.
A‐current modifies the spike of C‐type neurones in the rabbit nodose ganglion.
Authors: Ducreux C , Puizillout J J
Published: December 2014

1. In the rabbit nodose ganglion, C‐type fibre neurones (C neurones) can be divided into two subtypes according to their after‐hyperpolarizing potential (AHP) i.e. those with a fast AHP only and those with a fast AHP and a subsequent slow AHP produced by a slow calcium‐dependent potassium current. In addition we have shown that some C neurones can be divided into two groups according to the effect of membrane hyperpolarization on their spikes i.e. type 1 in which duration and amplitude do not change and type 2 in which duration and amplitude decrease significantly. 2. In the present report we studied the effect of A‐current (IA) on spike duration, amplitude and slow AHP using intracellular recording techniques. 3. To detect the presence of IA, we first applied a series of increasing rectangular hyperpolarizing pulses to remove IA inactivation and then a short depolarizing pulse to trigger a spike. In type 1 C neurones the lag time of the spike in relation to hyperpolarization remains constant whereas in type 2 C neurones the spike only appears after IA inactivation and lag time in relation to hyperpolarization is lengthened. Thus, type 2 C neurones have an IA while type 1 C neurones do not. The fact that addition of cadmium did not change the lag time in type 2 C neurones shows that the IA is not calcium dependent. 4. Nodose neurones can be orthodromically activated by stimulation of the vagal peripheral process. In this way, after a hyperpolarizing pulse, IA can be fully activated by the orthodromic spike itself. Under these conditions it is possible to analyse the effects of IA on the spike. This was done by increasing either the hyperpolarizing potential, pulse duration, or the delay of the spike after the end of the pulse. We observed that maximum IA inactivation removal was always associated with the lowest duration and amplitude of the spike. 5. When IA inhibitors, 4‐aminopyridine (4‐AP) or catechol, were applied to type 2 C neurones, the delay of the spike after the hyperpolarization‐depolarization test was no longer observed. In addition 4‐AP abolished the shortening of the duration of the spike induced by steady hyperpolarization. 6. In type 2 C neurones with slow AHP, the IA‐related decrease in spike duration was associated with a disappearance of the slow AHP. This indicates that IA decreases the calcium influx during the spike.(ABSTRACT TRUNCATED AT 400 WORDS)
Visceral vasodilatation and somatic vasoconstriction evoked by acid challenge of the rat gastric mucosa: diversity of mechanisms.
Authors: Wachter C , Heinemann A , Jocic M , Holzer P
Published: December 2014

1. Acid back‐diffusion through a disrupted gastric mucosal barrier increases blood flow to the stomach without any change in systemic blood pressure. This study was undertaken to examine the gastric acid‐evoked changes in blood flow in a number of visceral and somatic arterial beds and to elucidate the mechanisms which lead to the regionally diverse haemodynamic responses. 2. The gastric mucosa of urethane‐anaesthetized rats was challenged with acid by perfusing the stomach with ethanol (15%, to disrupt the gastric mucosal barrier) in 0.15 M HCl. Blood flow was estimated by laser Doppler flowmetry, the hydrogen clearance method or the ultrasonic transit time shift technique. 3. Gastric acid challenge increased blood flow in the gastric mucosa and left gastric artery while blood flow in the femoral artery and skin declined. 4. Afferent nerve stimulation by intragastric administration of capsaicin enhanced blood flow in the left gastric artery but did not diminish blood flow in the femoral artery when compared with the vehicle. 5. The gastric acid‐evoked dilatation of the left gastric artery was depressed by acute extrinsic denervation of the stomach, capsaicin‐induced ablation of afferent neurones or hexamethonium‐induced blockade of autonomic ganglionic transmission. 6. The gastric acid‐induced constriction of the femoral artery was attenuated by acute extrinsic denervation of the stomach but left unaltered by capsaicin, hexamethonium, guanethidine, indomethacin, telmisartan (an angiotensin II antagonist), [d(CH2)5(1), Tyr(Me)2, Arg8]‐vasopressin (a vasopressin antagonist), bosentan (an endothelin antagonist) and acute ligation of the blood vessels to the adrenal glands. 7. These data show that acid challenge of the gastric mucosa elicits visceral vasodilatation and somatic vasoconstriction via divergent mechanisms. The gastric hyperaemia is brought about by extrinsic vasodilator nerves, whereas the reduction of somatic blood flow seems to be mediated by non‐neural, probably humoral, vasoconstrictor messengers that remain to be identified.