bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective brain cooling in goats: effects of exercise and dehydration.
Authors: Baker M A , Nijland M J
Published: December 2014

1. Measurements of brain and central blood temperature (Tbr and Tbl), metabolic rate (MR) and respiratory evaporative heat loss (REHL) were made in trained goats walking on a treadmill at 4.8 km h‐1 at treadmill inclines of 0, 5, 10, 15 and 20% when they were fully hydrated and at 0% when they had been deprived of water for 72 h. 2. In hydrated goats, exercise MR increased progressively with increasing treadmill incline. Both Tbl and Tbr rose during exercise, but Tbl always rose more than Tbr, and selective brain cooling (SBC = Tbl ‐ Tbr) increased linearly with Tbl. Significant linear relationships were also present between REHL and Tbl and between SBC and REHL. Neither the slope of the regression relating SBC to Tbl nor the threshold Tbl for onset of SBC was affected by exercise intensity. Manual occlusion of the angularis oculi veins decreased SBC in a walking goat, while occlusion of the facial veins increased SBC. 3. Dehydrated goats had higher levels of Tbl, Tbr and SBC during exercise, but the relationship between SBC and Tbl was the same in hydrated and dehydrated animals. In dehydrated animals, REHL at a given Tbl was lower and SBC was thus maintained at reduced rates of REHL. 4. It is concluded that SBC is a linear function of body core temperature in exercising goats and REHL appears to be a major factor underlying SBC in exercise. The maintenance of SBC in spite of reduced REHL in dehydrated animals could be a consequence of increased vascular resistance in the facial vein and increased flow of cool nasal venous blood into the cranial cavity.
Effects of sympathetic nerve stimulation on the sino‐atrial node of the guinea‐pig.
Authors: Choate J K , Edwards F R , Hirst G D , O'Shea J E
Published: December 2014

1. The effects of sympathetic nerve stimulation on the generation of pacemaker action potentials, recorded from the sino‐atrial node of the guinea‐pig, were determined by using intracellular recording techniques. 2. Trains of stimuli applied to the right stellate ganglion led to an increase in heart rate after a delay of a few seconds. During the initial phase of the tachycardia the rate of discharge of pacemaker action potentials increased and the rate of diastolic depolarization increased, but both the peak diastolic potential and the maximum rate of rise of the action potentials were reduced. During the later phase of the tachycardia the peak diastolic potential, the amplitude of the action potentials, the maximum rate of rise and the rate of repolarization of the action potentials were increased. 3. When membrane potential recordings were made from sino‐atrial node cells, in which beating had been abolished by adding the organic calcium antagonist nifedipine, sympathetic nerve stimulation initiated excitatory junction potentials (EJPs) which had time courses similar to those of the tachycardias recorded from beating preparations. 4. Although both the tachycardias produced by either sympathetic nerve stimulation or added noradrenaline were largely abolished by beta‐adrenoceptor antagonists, the membrane potential changes recorded during the responses to sympathetic nerve stimulation or added noradrenaline were different. Bath‐applied noradrenaline caused a tachycardia which was associated with an increase in the amplitudes of pacemaker action potentials, an increase in the peak diastolic potential and a shortening in the duration of pacemaker action potentials. 5. The addition of agents which cause the accumulation of cyclic AMP in the cytoplasm of the cells produced a tachycardia which was associated with a similar sequence of changes in the membrane potentials to those produced by added noradrenaline; again the membrane potential changes produced by these agents differed from those produced by sympathetic nerve stimulation. 6. The results are discussed in relation to the idea that neurally released noradrenaline activates a set of receptors which cause tachycardia by increasing inward current flow during diastole, whereas added noradrenaline activates a set of receptors that are linked to a cyclic AMP‐dependent pathway which modifies the properties of some of the voltage‐dependent channels involved in pacemaking activity.
Synaptic‐ and agonist‐induced chloride currents in neonatal rat sympathetic preganglionic neurones in vitro.
Authors: Krupp J , Feltz P
Published: December 2014

1. By using the whole‐cell recording configuration of the patch‐clamp technique in a spinal cord slice preparation, we have made recordings from visually identified neurones in the lateral horn of the thoracic and lumbar spinal cord of neonatal rats (newborn to 14 days postnatal). 2. Some of the recorded neurones were labelled with the fluorescent dye Lucifer Yellow (n = 27). Their morphology was typical for sympathetic preganglionic neurones (SPNs). Based on the size of the cell soma and the electrophysiological properties, unlabelled neurones were also regarded as SPNs. 3. Spontaneous synaptic activity of different patterns could be observed in 73% of the recorded neurones (n = 106). It reversed at the chloride equilibrium potential (ECl) and could be reversibly blocked by strychnine (1‐10 microM), but not by bicuculline (10 microM) or SR95531 (5‐10 microM). 4. Synaptic activity could be elicited by focal electrical stimulation in the vicinity of the recorded neurone. These evoked synaptic events exhibited features similar to the spontaneous synaptic activity. 5. Application of glycine (100 microM‐1 mM) by a fast microperfusion system induced a chloride current in twenty‐seven out of thirty cells tested. The currents were reversibly blocked by strychnine (1‐10 microM), but were only weakly sensitive to bicuculline (10 microM). Stability of current responses to glycine was increased by inclusion of ATP (4 mM) in the intracellular medium. 6. Application of gamma‐aminobutyric acid (GABA; 100 microM‐1 mM) by the fast microperfusion system induced a chloride current in all twenty neurones tested. These currents were reversibly blocked by bicuculline (10 microM). Strychnine (1‐10 microM) blocked this current only weakly. Run‐down of GABA‐induced currents was prevented to a great extent by inclusion of ATP (4 mM) in the pipette. 7. These results suggest that the inhibitory synaptic activity recorded from SPNs in thin, transverse slices of neonatal rat spinal cord is mediated by glycine receptor‐gated Cl‐ channels. GABAA receptor‐gated Cl‐ channels might be activated by inputs from other spinal segments and/or descending pathways from higher brain regions.
Asynchrony of mossy fibre inputs and excitatory postsynaptic currents in rat hippocampus.
Authors: Langdon R B , Johnson J W , Barrionuevo G
Published: December 2014

1. Excitatory postsynaptic currents (EPSCs) were studied by whole‐cell voltage‐clamp recording (WCR) from pyramidal cells in the CA3 field of rat hippocampal slices. Input from mossy fibres was evoked by stimuli applied to stratum granulosum (‘dentate gyrus stimulation’). This often resulted in complex, multi‐component EPSCs with rise times as long as 5.0 ms (mean = 2.5 ms). In contrast, individual EPSC components typically had rise times between 0.3 and 1.0 ms. 2. To isolate monosynaptic, mossy fibre‐driven EPSC components, slices were exposed to 'suppressing’ media that reduced response amplitudes by 64‐88%. In five out of six cases, long EPSC rising phases (> 3 ms) retained the same shape during suppression. This implied that EPSCs were driven by asynchronously active mossy fibre inputs. 3. From latencies of antidromically driven granule cell population spikes (GCPSs) a mean conduction velocity of 0.67 m/s was inferred. Conduction distance had practically no correlation with GCPS duration, implying that velocity dispersion was small and did not desynchronize mossy fibre impulses. EPSC components exhibited 'surplus’ latency; they occurred 0.9‐4.8 ms after latencies expected on the basis of direct conduction distances. 4. Mossy fibre volleys (MFVs) were evoked by dentate gyrus stimulation and studied with neurotransmission disabled. MFV negative phases lasted from 2.5 to 4.5 ms and had multiple components. By comparison, negative phases of Schaffer collateral fibre volleys (SCFVs) were always simple in shape and lasted 1.5 ms or less. MFV components had surplus latencies similar to those of EPSC components. Late MFV components did not require high stimulus intensities. 5. Widespread activation of granule cells occurred when stimuli were applied to single loci in the stratum granulosum. This implies that such stimuli elicit antidromic impulses in hilar collaterals of mossy fibres, which could result in activation of orthodromic impulses in mossy fibre trunks that had not been stimulated directly. After anti‐, then orthodromic conduction, impulses would arrive in the CA3 subfield with 'surplus’ latency. 6. When cuts were made in the hilus to prevent anti‐/orthodromic conduction, MFV durations were reduced, but only to a small extent. This implies that surplus latency and asynchrony arise in part by anti‐/orthodromic conduction, and partly by a mechanism that is intrinsic to mossy fibres or their ‘giant’ boutons. 7. Because of desynchronization of mossy fibre inputs, there probably are significant differences between kinetic properties of averaged, compound mossy fibre EPSCs and those of unitary mossy fibre EPSCs (i.e. currents driven by input from single presynaptic axons).(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for the non‐existence of a negative phase in the hump charge movement component (I gamma) in Rana temporaria.
Authors: Hui C S , Chen W
Published: December 2014

1. Charge movement was studied in cut twitch fibres of Rana temporaria with a double Vaseline‐gap voltage‐clamp technique. 2. When charge movement was measured from stretched fibres (3.5 microns sarcomere length) bathed in a TEA‐Cl Ringer solution, the ON transients in the appropriate potential range showed an early I beta component followed by an I gamma hump. The late I gamma hump generally decayed monotonically towards the maintained current level. 3. On some rare occasions, the ON transient showed an undershoot immediately following the I gamma hump before reaching the steady‐state level. This dip in current, when it occurred, could only be observed in a very narrow potential range and might not persist until the end of the experiment. 4. A replacement of the Cl‐ in the external solution by CH3SO3‐ reduced the magnitude of the dip, suggesting that the dip is ionic in origin. 5. When charge movement was measured in slack fibres (2.2 microns sarcomere length, the probability of observing the dip in current was increased. 6. In some experiments in which the dip in current was very stable, the signal was studied by a sequence of TEST pulses to the same potential but with different durations. It was found that, if the dip in current was included as a negative phase of the I gamma hump, then the amount of ON charge was smaller than that of OFF charge. Also, as the pulse duration was increased progressively so that a longer portion of the dip was recorded, the OFF charge remained constant instead of being decreased.(ABSTRACT TRUNCATED AT 250 WORDS)
Myofibrillar ATPase activity and mechanical performance of skinned fibres from rabbit psoas muscle.
Authors: Potma E J , Stienen G J , Barends J P , Elzinga G
Published: December 2014

1. The relationship between energy turnover and mechanical performance was investigated in chemically skinned single fibres from rabbit psoas muscle at 15 degrees C, pH = 7.1, with MgATP, 5 mM; free Mg2+, 1 mM; ionic strength, 200 mM and sarcomere length, 2.4 microns by measuring force production and myofibrillar ATP turnover during isometric contractions as well as during repetitive changes in length. ATP hydrolysis was stoichiometrically coupled to the breakdown of NADH, which was measured photometrically via the absorption of near UV light at 340 nm. 2. Force and ATPase activity were measured during square‐wave length changes of different amplitudes (1‐10% of the fibre length, Lo) and different frequencies (2.5‐167 Hz). The average force during the length changes was less than the isometric value and decreased with increasing amplitude and frequency. At full activation (pCa 4.5), the isometric ATP turnover rate (+/‐ S.E.M.) was 2.30 +/‐ 0.05 s‐1 per myosin head. ATP turnover increased monotonically with increasing amplitude as well as with increasing frequency until saturation was reached. The greatest increase observed was 2.4 times the isometric value. 3. Force and ATPase activity were also determined for ramp shortenings followed by fast restretches. The average force decreased with increasing shortening velocity in a hyperbolic fashion. The ATP turnover increased with ramp velocity up to 0.5 L0 s‐1 and stayed almost constant (at 2.2 times the isometric value) for larger velocities. 4. Isometric force and ATPase activity both decreased as the calcium concentration was decreased. They did not vary in proportion at low Ca2+ concentrations, but this could largely be accounted for by the presence of a residual, Ca(2+)‐dependent, membrane‐bound ATPase. At high calcium concentrations ATPase activity during square‐wave length changes was higher than the isometric value, but at low calcium concentrations (pCa > 6.1), the ATPase activity during the length changes decreased below the isometric value and reached a minimum of 40% of the isometric level. 5. ATPase activity and average force obtained during changes in length show a high, movement protocol‐independent correlation. During the length changes the rate of ATP turnover divided by the average force level (tension cost) was larger than the isometric tension cost. The largest value found, for 10% length changes at 23 Hz, was 17 times the tension cost under isometric conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Human autonomic rhythms: vagal cardiac mechanisms in tetraplegic subjects.
Authors: Koh J , Brown T E , Beightol L A , Ha C Y , Eckberg D L
Published: December 2014

1. We studied eight young men (age range: 20‐37 years) with chronic, clinically complete high cervical spinal cord injuries and ten age‐matched healthy men to determine how interruption of connections between the central nervous system and spinal sympathetic motoneurones affects autonomic cardiovascular control. 2. Baseline diastolic pressures and R‐R intervals (heart periods) were similar in the two groups. Slopes of R‐R interval responses to brief neck pressure changes were significantly lower in tetraplegic than in healthy subjects, but slopes of R‐R interval responses to steady‐state arterial pressure reductions and increases were comparable. Plasma noradrenaline levels did not change significantly during steady‐state arterial pressure reductions in tetraplegic patients, but rose sharply in healthy subjects. The range of arterial pressure and R‐R interval responses to vasoactive drugs (nitroprusside and phenylephrine) was significantly greater in tetraplegic than healthy subjects. 3. Resting R‐R interval spectral power at respiratory and low frequencies was similar in the two groups. During infusions of vasoactive drugs, low‐frequency R‐R interval spectral power was directly proportional to arterial pressure in tetraplegic patients, but was unrelated to arterial pressure in healthy subjects. Vagolytic doses of atropine nearly abolished both low‐ and respiratory‐frequency R‐R interval spectral power in both groups. 4. Our conclusions are as follows. First, since tetraplegic patients have significant levels of low‐frequency arterial pressure and R‐R interval spectral power, human Mayer arterial pressure waves may result from mechanisms that do not involve stimulation of spinal sympathetic motoneurones by brainstem neurones. Second, since in tetraplegic patients, low‐frequency R‐R interval spectral power is proportional to arterial pressure, it is likely to be mediated by a baroreflex mechanism. Third, since low‐frequency R‐R interval rhythms were nearly abolished by atropine in both tetraplegic and healthy subjects, these rhythms reflect in an important way rhythmic firing of vagal cardiac motoneurones.
Benzodiazepine and beta‐carboline regulation of single GABAA receptor channels of mouse spinal neurones in culture.
Authors: Rogers C J , Twyman R E , Macdonald R L
Published: December 2014

1. The effects of the benzodiazepine receptor agonist, diazepam (DZ), and the inverse agonist, methyl‐6,7‐dimethoxy‐4‐ethyl‐beta‐carboline‐3‐carboxylate (DMCM), on gamma‐aminobutyric acid (GABAA) receptor single channel currents were characterized. Outside‐out patches were obtained from somata of cultured mouse spinal cord neurones and voltage clamped at ‐75 mV (ECl = 0 mV). 2. GABA (2 microM) alone or with DZ (20‐1000 nM) or DMCM (20‐100 nM) was applied to patches by pressure ejection from blunt micropipettes. DZ enhanced GABAA receptor currents with an inverted U‐shaped concentration‐response curve. Mean steady‐state currents were increased by low concentrations of DZ (20‐50 nM). At higher concentrations of DZ, the enhancement was diminished. Mean steady‐state currents were decreased by DMCM at all concentrations. 3. GABAA receptor channels opened most frequently to a 27 pS main conductance level and less frequently to a 19 pS subconductance level. Neither DZ nor DMCM altered the proportion of time spent at either of the conductance levels. The kinetic properties of the main conductance level were studied. 4. Neither DZ nor DMCM altered the mean GABAA receptor channel open or burst durations. Sums of three exponential functions were required to fit best open and burst duration‐frequency histograms for GABA alone or with DZ or DMCM. No significant changes in the three time constants or areas of the three exponential functions for open or burst duration histograms were produced by DZ or DMCM. 5. With increasing concentrations of DZ up to 50 nM, GABA evoked an increased frequency of channel openings and bursts. With higher DZ concentrations, the magnitudes of the increase in channel opening and burst frequencies were reduced. At all concentrations of DMCM, GABA evoked a decreased frequency of channel openings and bursts. 6. Closed duration‐frequency histograms for GABA alone or with DZ or DMCM were best fitted by sums of at least six exponential functions. The three shortest closed duration time constants were unchanged by DZ or DMCM. The three longest closed duration time constants were altered by DZ and DMCM, consistent with alterations in opening frequency. 7. DZ increased and DMCM decreased steady‐state GABAA receptor current by increasing or decreasing channel opening frequency without altering mean channel open duration. We propose that DZ and DMCM alter GABAA receptor current by acting reciprocally to increase or decrease only, respectively, the apparent agonist association rate at the first of two proposed GABA binding steps without altering channel gating.(ABSTRACT TRUNCATED AT 400 WORDS)
Photolytic manipulation of Ca2+ and the time course of slow, Ca(2+)‐activated K+ current in rat hippocampal neurones.
Authors: Lancaster B , Zucker R S
Published: December 2014

1. Experiments were performed on hippocampal CA1 pyramidal cells to investigate the time course of a slow, Ca(2+)‐activated K+ current that follows a burst of action potentials. At a temperature of 27‐30 degrees C, this current rises to a peak 200‐400 ms following the cessation of Ca2+ entry before decaying to baseline in 4‐8s. 2. Intracellular recordings were made using electrodes containing the photolabile calcium buffers nitr‐5 or DM‐nitrophen loaded appropriately with Ca2+. Under these conditions, photolysis of the compound using an ultraviolet flashlamp caused an instantanous increase in cytoplasmic Ca2+ throughout the cell. The response to flash photolysis was a membrane hyperpolarization with an onset limited by the membrane time constant. Multiple (up to twenty) flash responses could be generated. 3. The postspike slow after‐hyperpolarization (AHP) and flash‐induced hyperpolarizations showed a common sensitivity to the beta‐adrenergic receptor agonist isoprenaline. 4. Following a burst of spikes, the current underlying an AHP in progress could be terminated or reduced by photolysis‐induced production of calcium buffer from diazo‐4 within the cell. This action was rapid (within the setting time of the flash artifact, i.e. < 10 ms) despite the fact that the manipulation occurred 400‐500 ms following the end of Ca2+ entry. 5. Partial block of the slow AHP by buffer production was accompanied by an increase in the time to peak of the event. 6. The time to peak of the slow AHP could also be manipulated by experiments which altered the spatial distribution of Ca2+ entry, such as production of calcium spikes or dendritic depolarization by glutamate in the presence of tetrodotoxin. 7. The Ca(2+)‐dependent K+ current responsible for the slow AHP responds immediately to increase or decreases in cytoplasmic Ca2+. It seems likely, therefore, that the slow AHP is controlled solely by changes in free Ca2+ and that the time course is governed by the redistribution of cytoplasmic Ca2+ following activity‐induced entry through voltage‐ or receptor‐operated channels.
Sympathetic activity recorded from the rat caudal ventral artery in vivo.
Authors: Johnson C D , Gilbey M P
Published: December 2014

1. In twenty‐five sodium pentobarbitone (alpha‐chloralose supplemented)‐anaesthetized, artificially ventilated and paralysed rats, postganglionic sympathetic single unit activity was recorded at the level of the adventitia of the caudal ventral artery of the tail using a focal recording technique. 2. Ten units were identified as being sympathetic in nature, as they were activated following electrical stimulation of the lumbar sympathetic chain. The on‐going activity of seven of these was blocked by hexamethonium (6‐12 mg kg‐1). 3. The units were not under tonic baroreceptor modulation, as indicated by the lack of pulse modulation of discharge. Respiratory modulation was apparent, with neurones firing mainly during expiration (phrenic silence), and activity was influenced also by the lung inflation cycle. Whole‐body warming decreased unit activity. 4. Interspike interval and autocorrelation analysis showed that unit discharge was dominated by the respiratory rhythm and that units tended to discharge in bursts (often duplets). It is suggested that the intraburst interval may be determined by a hypothetical sympathetic oscillator. 5. This study presents the first analysis of single unit activity recorded in vivo from sympathetic fibres innervating an identified blood vessel.
Transmission at the squid giant synapse was blocked by tetanus toxin by affecting synaptobrevin, a vesicle‐bound protein.
Authors: Llinás R , Sugimori M , Chu D , Morita M , Blasi J , Herreros J , Jahn R , Marsal J
Published: December 2014

1. The effect of whole tetanus toxin (TeTX) and of its light chain (TeTX L‐chain) on transmitter release was determined by presynaptic pressure‐injection in the squid giant synapse. 2. The results indicate that whole TeTX does not modify transmission while the L‐chain blocks transmission within 20‐30 min. This block does not involve changes in the sodium or potassium conductances responsible for spike generation or the voltage‐dependent presynaptic calcium current responsible for transmitter release. 3. Western blotting of protein fractions from the squid optic lobe demonstrated the presence of a protein which reacted with specific antibodies against mammalian synaptobrevin, a vesicular protein. In addition, this protein was enzymatically cleaved by the L‐chain component of the toxin in a similar fashion to its mammalian counterpart. 4. These results demonstrate that TeTX L‐chain toxin acts directly on a squid synaptobrevin and prevents synaptic release probably by interfering with the docking‐fusion synaptic vesicles at the active zone.
Effect of formate and oxalate on fluid reabsorption from the proximal convoluted tubule of the anaesthetized rat.
Authors: Wareing M , Green R
Published: December 2014

1. It has recently been suggested that both formate and oxalate may be involved in the reabsorption of chloride from the proximal convoluted tubule (PCT). Reabsorption is achieved via a mechanism coupling Na(+)‐H+ exchange to Cl(‐)‐anion exchange thus facilitating net NaCl transport. This possible mechanism was investigated further by observing the effect of luminal addition of formate and oxalate on proximal tubule transport in anaesthetized rats, previously prepared for in vivo microperfusion. 2. Addition of formate (0.25 mmol l‐1) to the luminal perfusate resulted in a significant stimulation of fluid reabsorptive rate. 3. Oxalate was found to have a concentration‐dependent effect on fluid reabsorption. Luminal oxalate concentrations below 0.05 mmol l‐1 stimulated fluid reabsorption, while an oxalate concentration of 0.5 mmol l‐1 inhibited fluid reabsorption. 4. The presence of formate (0.25 mmol l‐1) and oxalate (0.001 mmol l‐1) in the same luminal perfusate stimulated fluid reabsorption from the proximal tubule lumen, but the effects of formate and oxalate were not additive. 5. The removal of bicarbonate from the luminal perfusate and its replacement with phosphate had no significant effect on fluid reabsorptive rate. An alteration in perfusate pH was also ineffective. Addition of oxalate at high and low pH failed to stimulate fluid reabsorption compared with pH‐matched control perfusions. 6. The experimental data suggest the involvement of both formate and oxalate in the reabsorption of NaCl from the proximal tubule lumen, though their influence may not be exerted through the same mechanisms.
Omega‐conotoxin‐sensitive and ‐resistant transmitter release from the chick ciliary presynaptic terminal.
Authors: Yawo H , Chuhma N
Published: December 2014

1. Synaptically evoked responses to stimulation of the oculomotor nerve were recorded from the ciliary nerve in chick embryos. The postsynaptic currents in response to presynaptic stimulation (EPSCs) were also recorded under whole‐cell voltage clamp of the ciliary cell. 2. The ciliary nerve response was dependent on the extracellular Ca2+ concentration ([Ca2+]o). omega‐Conotoxin GVIA (omega‐CgTX, 100 nM) increased the [Ca2+]o necessary to evoke the half‐maximal response by a factor of 1.7 without changing the slope of [Ca2+]o dependence. Dihydropyridine (DHP) derivatives, nifedipine or Bay K 8644, did not affect the [Ca2+]o sensitivity of ciliary nerve response. 3. The EPSC was usually preceded by the capacitive coupling response of the presynaptic action potential. In some records, the EPSCs were also preceded by the electrical coupling responses which were the mirror images of the presynaptic action potentials. The current‐voltage relation of the EPSCs showed inward rectification. 4. The EPSC was potentiated by 4‐aminopyridine (4‐AP) as a result of prolongation of the falling phase of presynaptic action potential. In the presence of high [Ca2+]o and 4‐AP, a small fraction of EPSC was resistant to omega‐CgTX. 5. The resting potential of the presynaptic terminal was changed from ‐69 to ‐57 mV by increasing [K+]o from 1 to 10 mM. The same procedure decreased the omega‐CgTX‐resistant EPSC by 30%, whereas the omega‐CgTX‐untreated EPSC in low‐Ca2+ saline was not affected by the change in [K+]o. 6. The nerve‐evoked increase in intracellular Ca2+ was recorded from the presynaptic terminal (delta[Ca2+]pre). The delta[Ca2+]pre was larger in a solution containing 10 mM Ca2+ and 1 mM K+ after treating with omega‐CgTX than in a solution containing 2 mM Ca2+ and 16 mM Mg2+ before treating with omega‐CgTX. The EPSC was, in contrast, smaller in the 10 mM Ca(2+)‐1 mM K+ solution after omega‐CgTX treatment than in the 2 mM Ca(2+)‐16 mM Mg2+ solution before omega‐CgTX treatment. 7. Similarly, the EPSC was smaller in the 10 mM Ca(2+)‐1 mM K+ solution containing 5 microM La3+ than in the 2 mM Ca(2+)‐16 mM Mg2+ solution, whereas the delta [Ca2+]pre was larger in the 10 mM Ca(2+)‐1 mM K+ solution containing 5 micrograms La3+ than in the 2 mM Ca(2+)‐16 mM Mg2+ solution. 8. It is concluded that the omega‐CgTX‐sensitive Ca2+ conductance of the presynaptic terminal is the principal source of Ca2+ involved in transmitter release.(ABSTRACT TRUNCATED AT 400 WORDS)
Long‐term facilitation of inspiratory intercostal nerve activity following carotid sinus nerve stimulation in cats.
Authors: Fregosi R F , Mitchell G S
Published: December 2014

1. Repeated carotid sinus nerve (CSN) stimulation evokes a serotonin‐dependent long‐term facilitation (LTF) of phrenic nerve activity in cats. To determine whether CSN stimulation‐evoked LTF is a general property of spinal inspiratory motoneurones, phrenic and inspiratory internal intercostal (IIC) nerve activities were recorded in nine cats (eight anaesthetized; one decerebrate), which were vagotomized, paralysed, thoracotomized and ventilated with O2; airway CO2 was controlled by means of of a servo‐respirator. Baseline conditions were established by setting the arterial CO2 pressure (Pa,CO2) at approximately 2 mmHg above the threshold for IIC activity. One CSN was stimulated (3 times threshold, 25 Hz, 0.5 ms duration) with five (2 min) trains, each separated by 5 min. 2. The peak integrated phrenic activity was elevated by 33% whereas IIC activity was elevated by 226% above baseline, 90 min post‐stimulation (P < 0.05). The results were similar when expressed as a percentage of the maximal neural activities (elicited by combined hypercapnia and CSN stimulation), although differences between the nerves were less pronounced. The burst frequency was not change following stimulation. 3. In five additional cats that were pretreated with the serotonin receptor antagonist, methysergide maleate (0.5‐1 mg kg‐1, I.V.), the CO2 thresholds of the phrenic (12 mmHg) and IIC nerves (22 mmHg) were increased (P < 0.05), and LTF could not be elicited in either neurogram. 4. Successive CSN stimulation episodes evoked a previously undescribed phenomenon. Although the peak integrated phrenic activity was unchanged (90‐95% of maximal), IIC activity increased progressively during successive stimulus episodes (66‐90% of maximal; P < 0.05). However, after methysergide treatment, the initial stimulus‐evoked phrenic response decreased to 58% of maximal and both neurograms exhibited progressive augmentation of the stimulus‐evoked response. As stimulus‐evoked augmentation does not require serotonin, it is independent of LTF. 5. We conclude that CSN stimulation‐evoked LTF of IIC activity exceeds that of phrenic activity. Since LTF requires the neuromodulator serotonin and is expressed predominantly by changes in burst pattern formation versus rhythm generation, serotonin may exert a greater influence on IIC relative to phrenic respiratory motor output. A unique mechanism is described whereby successive CSN stimulus episodes cause progressively increasing responses in both neurograms.
The effect of rapid local cooling on human finger nailfold capillary blood pressure and blood cell velocity.
Authors: Hahn M , Shore A C
Published: December 2014

1. The effect of a rapid local reduction in finger temperature on finger nailfold capillary blood pressure and blood cell velocity was investigated in healthy subjects. 2. Cooling was achieved by placing the finger into an adjustable copper cylindrical finger holder, which incorporated a Peltier element within its base; thus the entire finger from just distal to the nailfold to the interphalangeal joint was cooled. The Peltier element was cooled to 8 degrees C for 5 min. 3. Finger tip temperature was reduced to 76 +/‐ 12% of its resting value during cooling (28.8 +/‐ 4.8 degrees C (mean +/‐ S.D.) baseline versus 22.1 +/‐ 6.4 degrees C in the fifth minute of cooling, P = 0.012); this was accompanied by a reduction in capillary blood cell velocity similar to that described previously in cooling experiments using cold air (baseline median, 671 microns s‐1 (range, 29‐4421 microns s‐1) versus median during cooling, 221 microns s‐1 (range, 6.7‐2579 microns s‐1), P = 0.012). 4. The magnitude and timing of the capillary pressure response to cooling and recovery varied between individuals. In the group as a whole, there was no significant fall in capillary pressure during cooling (basal before cooling, 16.7 +/‐ 3.7 mmHg versus minimum during cooling, 15.1 +/‐ 3.5 mmHg, P = 0.12), whereas capillary pulse pressure amplitude was reduced (basal before cooling, 5.3 +/‐ 3.1 mmHg versus minimum during cooling, 3.7 +/‐ 2.6 mmHg, P = 0.028). 5. During the recovery phase, post cooling, both capillary pressure and capillary pulse pressure amplitude were markedly elevated compared to baseline or the cooling phase.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of metabolic inhibitors and second messengers upon Na(+)‐H+ exchange in the sheep cardiac Purkinje fibre.
Authors: Wu M L , Vaughan-Jones R D
Published: December 2014

1. Acid extrusion through Na(+)‐H+ exchange was studied in the sheep cardiac Purkinje fibre (bathed in Hepes‐buffered solution, nominally free of CO2‐HCO3‐) by examining (i) intracellular pH (pHi) recovery from an intracellular acid load (induced by 20 mM NH4Cl prepulse) and (ii) the rate of rise of intracellular Na+ activity (aiNa) following the ammonium prepulse (used as an estimate of apparent Na+ influx on Na(+)‐H+ exchange). The pHi and aiNa were recorded using ion‐selective microelectrodes. 2. The pHi recovery and rise of aiNa were both greatly slowed in the presence of 2‐deoxyglucose (DOG; glucose‐free solution), an inhibitor of glycolysis, indicating inhibition of Na(+)‐H+ exchange. 3. Cyanide moderately slowed pHi recovery rate but did not significantly affect the rise of aiNa. Estimates of beta 1 (intracellular buffering power) indicated an increase of approximately 50% in the presence of cyanide; such an increase accounts for most of the observed slowing of pHi recovery. It is concluded that oxidative inhibition with cyanide does not inhibit Na(+)‐H+ exchange. 4. Intracellular ATP, measured from luciferin‐luciferase luminescence, was reduced by a similar amount (approximately 70%) by either DOG or cyanide. This suggests that, if intracellular ATP (ATPi) reduction is the cause of exchanger inhibition by metabolic inhibitors, then ATPi generated glycolytically is more important for activation of the exchange. 5. 3‐Isobutyl‐1‐methylxanthine (IBMX; a non‐specific phosphodiesterase inhibitor which can elevate intracellular [cAMP]) slowed acid extrusion and reduced apparent Na+ influx by a similar amount, whereas addition of sodium nitroprusside (to elevate intracellular [cGMP]) had no effect, suggesting that raising intracellular [cAMP] downregulates Na(+)‐H+ exchange, whereas raising intracellular [cGMP] does not. 6. Application of trifluorperazine (TFP; a non‐specific calcium‐calmodulin inhibitor) completely reversed the inhibitory effects of IBMX upon pHi recovery and aiNa. Under control conditions (no IBMX), TFP had no effect on pHi recovery or upon resting pHi. 7. The phorbol ester 12‐O‐tetradecanoyl phorbol 13‐acetate (TPA) had no significant effect on pHi recovery or apparent Na+ efflux. 8. We conclude that inhibition of glycolysis or elevation of cAMP produces downregulation of Na(+)‐H+ exchange in the cardiac Purkinje fibre. Possible reasons for the lack of inhibitory effect of oxidative inhibitors are discussed.
Ca2+ load of guinea‐pig ventricular myocytes determines efficacy of brief Ca2+ currents as trigger for Ca2+ release.
Authors: Han S , Schiefer A , Isenberg G
Published: December 2014

1. In guinea‐pig ventricular cells, the concentration of ionized cytosolic calcium ([Ca2+]o) was estimated from the fluorescence of 100 microM K5‐indo‐1. At 36 degrees C and 2 mM [Ca2+]o, the Ca2+ load of the cells was varied by 1 Hz trains of conditioning clamp pulses to ‐30 mV (low Ca2+ load), 0 mV (intermediate Ca2+ load) and paired pulses (high Ca2+ load). After seven pulses potentiation was steady and short test pulses to 0 mV were tested for their efficacy in triggering [Ca2+]c transients. The influx of trigger Ca2+ was graded by varying the test‐pulse duration between 1 and 180 ms. 2. After a 3 min rest period, [Ca2+]c was 100 +/‐ 20 nM (mean +/‐ S.E.M.) and 2 ms test pulses were unable to induce [Ca2+]c transients. Test pulses of 2 ms duration, however, induced [Ca2+]c transients after potentiation with single or paired pulses. 3. At high cellular Ca2+ load, the amplitude of the [Ca2+]c transients (delta[Ca2+]c) gradually increased with pulse durations up to 8 ms. Pulse durations between 8 and 160 ms, however, did not further increase delta[Ca2+]c as if the largest part of the [Ca2+]c transient was due to regenerative contribution of Ca(2+)‐induced Ca2+ release. 4. Pulses of 160 ms duration induced ‘saturating’ responses whose amplitudes delta[Ca2+]c, t = infinity decreased from 938 +/‐ 120 nM at high Ca2+ load, to 610 +/‐ 90 and 350 +/‐ 120 nM at intermediate and low Ca2+ loads, respectively. 5. Delta[Ca2+]c was more sensitive to the duration of Ca2+ influx at low or intermediate Ca2+ loads than at high Ca2+ load. When delta[Ca2+]c was plotted against the test‐pulse duration, 50% of delta[Ca2+]c, t = infinity was found to be at 9 +/‐ 2 ms (low), 4.6 +/‐ 1 ms (intermediate) or 1.8 +/‐ 0.5 ms pulses (high Ca2+ load). Correspondingly, the efficacy of 2 ms test pulses in triggering [Ca2+]c transients increased with the Ca2+ load. 6. At high Ca2+ load, [Ca2+]c peaked nearly independently of pulse duration at 19 +/‐ 3 ms. At intermediate or low Ca2+ load, time to peak increased with pulse duration. 7. The results confirm the theory that sarcoplasmic reticulum (SR) Ca2+ release contributes an amount to the [Ca2+]c transient that increases with the cellular Ca2+ load. The results are compatible with the hypothesis that SR Ca2+ release can be activated by both Ca2+ influx and by SR Ca2+ release and that the latter mechanism constitutes a positive feedback, the amplification of which increases with the amount of releasable Ca2+.
Intramural neural pathways between the duodenum and sphincter of Oddi in the Australian brush‐tailed possum in vivo.
Authors: Saccone G T , Harvey J R , Baker R A , Toouli J
Published: December 2014

1. Balloon distension of the duodenum 2 cm oral or anal to the sphincter of Oddi‐duodenal junction elevated the amplitude of spontaneous sphincter of Oddi phasic contractions by 37.7 +/‐ 8.5 or 120.1 +/‐ 79.8%, respectively (mean +/‐ S.E.M., both n = 6, P < 0.05, Wilcoxon test). To further investigate this response, this study aimed to determine if: (i) electrical field stimulation (EFS) of the duodenum influences sphincter of Oddi activity; (ii) intramural nerves mediate the response; and (iii) nicotinic and/or muscarinic receptors are involved. 2. Electrical field stimulation (70 V, 0.5 ms; 5‐60 Hz, 10‐20 s) of the duodenal anterior serosal surface 2‐4 cm oral or anal to the sphincter of Oddi‐duodenal junction, produced excitatory responses in the sphincter of Oddi in anaesthetized Australian brush‐tailed possums (n = 45). 3. These responses were frequency dependent, maximal at 30 Hz (n = 4) and abolished by tetrodotoxin (9 micrograms kg‐1 I.A.; n = 6), or by crushing the duodenum (n = 3). Hexamethonium bromide (30 mg kg‐1 I.V.) did not significantly alter the response to duodenal EFS either oral (n = 6) or anal (n = 8) to the sphincter of Oddi‐duodenal junction. Atropine sulphate (30 micrograms kg‐1 I.V.) reduced the response to duodenal EFS oral and anal to the sphincter of Oddi‐duodenal junction to 11.2 +/‐ 5.8 (n = 6) and 45.0 +/‐ 26.8% (n = 8), respectively (both P < 0.05). 4. Bilateral cervical vagotomy and guanethidine infusion (10 mg kg‐1 over 15 min I.V.) did not significantly alter the responses to duodenal EFS (n = 7). 5. Excitatory intramural neural pathways between the sphincter of Oddi and the segment of duodenum 4 cm oral and anal to the sphincter of Oddi‐duodenal junction have been demonstrated. These postganglionic pathways may involve muscarinic receptors.
Block by 4‐aminopyridine of a Kv1.2 delayed rectifier K+ current expressed in Xenopus oocytes.
Authors: Russell S N , Publicover N G , Hart P J , Carl A , Hume J R , Sanders K M , Horowitz B
Published: December 2014

1. The blocking action of 4‐aminopyridine (4‐AP) on a delayed rectifier Kv1.2 K+ channel expressed in oocytes was investigated at room temperature (22 degrees C) and physiological temperature (34 degrees C) using the double‐electrode voltage clamp and patch clamp techniques. 2. At room temperature, 4‐AP (100 microM) inhibition occurred only after activation of current. The rate of onset of block was dependent upon the length of time current was activated by a depolarizing step. Similarly, removal of block required current activation. The degree of steady‐state block by 4‐AP was not reduced by increasingly more depolarized step potentials. The degree of steady‐state block also did not change over the duration of a 1 s step. 3. When channels were nearly fully inactivated, 4‐AP produced no additional block of a subsequent depolarizing step, suggesting that 4‐AP did not bind when channels were in the inactivated state. In single channel experiments, 4‐AP decreased the mean open time in a dose‐dependent manner but did not alter the single‐channel current amplitude. 4. At 34 degrees C the I‐V relationship and inactivation curve shifted to more negative potentials. Increasing the temperature to 34 degrees C did not alter the degree of block by 4‐AP, although the rate of onset of block was greatly enhanced. 5. Results suggest that 4‐AP binds to the open state of the Kv1.2 channel and is trapped when the channel closes. 4‐AP cannot bind when the channel is closed or inactivated prior to the addition of the drug. C‐type inactivation and 4‐AP binding to the channel are mutually exclusive. A model for the proposed mechanism of action of 4‐AP on the Kv1.2 channel is proposed based on experimental data.
Transient and long‐lasting actions of 5‐HT on rat dentate gyrus neurones in vitro.
Authors: Piguet P , Galvan M
Published: December 2014

1. The actions of 5‐hydroxytryptamine (5‐HT) on rat dentate gyrus neurones were measured with conventional intracellular recording techniques in brain slices maintained in vitro at 32 degrees C. 2. Bath application of 5‐HT (0.3‐100 microM) hyperpolarized the membrane potential and reduced the input resistance; these effects persisted in tetrodotoxin (1 microM) and were abolished by MDL 73,005EF, a 5‐HT1A receptor antagonist. 3. Local application of 5‐HT via a pressure pipette also elicited a hyperpolarization and a reduction in resistance, and evoked a transient ‘burst’ of spontaneous inhibitory postsynaptic potentials (IPSPs) which were blocked by tetrodotoxin or bicuculline. 4. The ‘burst’ of IPSPs was subject to desensitization. It was completely abolished in the presence of the 5‐HT3 receptor antagonist dolasetron. 5. In some cells, a longer lasting increase in spontaneous IPSP frequency was observed during application of 5‐HT; this effect was blocked by the 5‐HT2 receptor antagonist MDL 100,907. 6. 5‐HT (30 microM) shortened the decay time constants of the glutamatergic and GABAergic evoked EPSPs and IPSPs without changing their amplitudes. 7. It is concluded that 5‐HT hyperpolarizes granule cells via postsynaptic 5‐HT1A receptors and increases spontaneous GABA release from inhibitory interneurones via the activation of 5‐HT3 receptors and/or 5‐HT2 receptors.
The role of the Na(+)‐Ca2+ exchanger in the rate‐dependent increase in contraction in guinea‐pig ventricular myocytes.
Authors: Harrison S M , Boyett M R
Published: December 2014

1. The intracellular sodium activity (alpha Na1), contraction and membrane current were recorded simultaneously in voltage‐clamped guinea‐pig ventricular myocytes. 2. Increasing the frequency (from 0.5 to 3 Hz) of voltage clamp pulses to 0 mV from a holding potential of ‐80 mV led to an increase in both alpha Na1 and contraction. The rate‐dependent increase in contraction was reduced by 25 microM tetrodotoxin (TTX) and abolished with a holding potential of ‐40 mV. There was no rate‐dependent rise in alpha Na1 with a holding potential of ‐40 mV. These results suggest an important role for alpha Na1 and in particular Na+ influx via Na+ channels during rate‐dependent changes in contraction. 3. After an increase in frequency from 0.5 to 3 Hz, membrane current at the end of voltage clamp pulses became progressively more outward and the tail current upon at repolarization became progressively more inward compared with those recorded at 0.5 Hz. TTX reduced the magnitude of both the outward and inward rate‐dependent shifts of current. 4. The addition of extracellular CsCl blocked the inward rectifier potassium current (IK.1) and the delayed rectifier (IK), but did not change the rate‐dependent shift in current. 5. The difference between current‐voltage relationships at 0.5 and 3 Hz showed that the rate‐dependent outward shift of current at the end of voltage clamp pulses was small at potentials negative to ‐20 mV, was larger at more positive potentials and was reduced by TTX at most potentials. The TTX‐sensitive component reversed at ‐47 mV. 6. These results are consistent with a net increase in outward Na(+)‐Ca2+ exchange current during a voltage clamp pulse in response to the rise of alpha Na1. The increase in outward current (resulting from either enhanced Ca2+ influx or reduced Ca2+ efflux) will augment the Ca2+ load of the cell and contribute to the rate‐dependent increase in contraction.
Baroreceptor influence on the relationships between discharges of different sympathetic nerves of the cat.
Authors: Kocsis B
Published: December 2014

1. The sympathetic nerve discharge (SND) of three different nerves and the arterial blood pressure (BP) were recorded simultaneously in baroreceptor‐intact cats. The linear correlation between different nerve pairs was characterized by the coherence spectrum and its baroreceptor‐related component was estimated by partialization of the coherence on the basis of the blood pressure signal. 2. The SND‐SND coherence values were higher than those found earlier in baroreceptor‐denervated cats. As shown by partial coherence analysis, in about 50% of the experiments with high SND‐BP coherence (25 nerve pair recordings), this could be explained by superposition of the effects of common central sources of activity and of the additional common rhythmic input from the baroreceptors. Partialization was ineffective in 50% of the experiments with high SND‐BP coherence (22 nerve pairs) and also when the SND‐BP coherence was relatively low (17 nerve pairs). On the group average, after elimination of the components explained by baroreceptor influence, the peak SND‐SND coherence no longer correlated with the SND‐BP coherence and both the numerical values and the relative pattern of coherences between different nerves became similar to those characteristic for baroreceptor‐denervated cats. 3. It is suggested that the method used in this study represents a ‘theoretical barodenervation’ and may be of great value in experiments, when surgical or chemical denervation of the baroreceptors does not represent a real option, e.g. in human subjects.