bluuebunny/crossref_metadata_2025 huggingface dataset:
Inactivating and non‐inactivating dihydropyridine‐sensitive Ca2+ channels in mouse cerebellar granule cells.
Authors: Slesinger P A , Lansman J B
Published: December 2014

1. Granule cells were dissociated from mouse cerebellum and grown in vitro. Currents through single Ca2+ channels were recorded from the cell body with the patch clamp technique. 2. Voltage steps to 0 mV produced brief channel openings with a mean open time of approximately 0.5 ms. The single‐channel conductance measured from the amplitude of the single‐channel current with 90 mM‐Ba2+ in the patch electrode was 22 pS. 3. The probability of Ca2+ channel opening increased with test potentials more positive than ‐30 mV, with half‐activation near 0 mV, and followed the Boltzmann relation for the activation of whole‐cell Ca2+ current. 4. Voltage steps to potentials more positive than 0 mV produced more channel activity at the beginning than at the end of the voltage step. The average of the single‐channel currents decayed to a non‐zero level with a time course similar to that of the whole‐cell Ca2+ current. 5. The amplitude as well as the decay of the mean current measured during a test pulse to 0 mV was reduced as the holding potential was made more positive than approximately ‐90 mV. The change in the open channel probability with holding potential followed the Boltzmann relation which described the inactivation of the whole‐cell Ca2+ current. 6. Ca2+ channel activity persisted for over several minutes after excising the patch from the cell body when intracellular cyclic AMP was increased. After patch excision, the number of functional channels decreased to a level where only one channel at a time was active. Ca2+ channel openings appeared as either short bursts at the beginning of the voltage step or long bursts that lasted throughout the pulse. 7. Exposing the cell to the dihydropyridine agonist +(S)‐202‐791 markedly increased the fraction of sweeps with long openings and produced a non‐decaying mean current that was approximately 5 times larger than control. In a fraction of the sweeps, however, long openings occurred more frequently at the beginning than at the end of the voltage step and these produced a decaying mean current. 8. Shifting the holding potential to more positive potentials in the presence of the dihydropyridine agonist preferentially reduced the number of brief openings while sparing the long openings. The amplitude of the mean current was similar to that obtained from the more negative holding potential and there was no change in the fraction of sweeps with long openings that occurred at the beginning of the voltage pulse.(ABSTRACT TRUNCATED AT 400 WORDS)
The cortical drive to human respiratory muscles in the awake state assessed by premotor cerebral potentials.
Authors: Macefield G , Gandevia S C
Published: December 2014

1. We investigated the possibility of a cortical contribution to human respiration by recording from the scalp of awake subjects the premotor cerebral potentials that are known to precede voluntary limb movements. 2. Electroencephalographic activity (EEG) was recorded from scalp electrodes and averaged for 1.8‐2.0 s before the time at which airway pressure exceeded an inspiratory or expiratory threshold. Clear premotor cerebral potentials were recorded during brisk, self‐paced nasal inhalations or exhalations. In ten subjects, a slow cortical negativity (Bereitschaftspotential) was apparent in the averaged EEG, commencing 1.2 +/‐ 0.3 s before the onset of inspiratory (scalene) or expiratory (abdominal) muscle activity (EMG). It was maximal at the vertex, with a mean slope of 12.3 +/‐ 5.8 microV/s, and was followed by a post‐movement positivity. 3. In four subjects the inspiratory premotor potential culminated in a large negativity, the motor potential, which began 24 +/‐ 15 ms before the onset of scalene EMG. It is argued that such a short latency is consistent with a volitionally generated respiratory command which travels relatively directly to the respiratory muscles, having a total central delay which is no longer than that for voluntary finger movements. 4. That the respiratory premotor and motor potentials did not originate in subcortical structures was supported by their absence in a patient suffering from chronic reflexogenic hiccups, in whom cerebral activity was back‐averaged from each brisk hiccup. 5. During quiet breathing, in which subjects were relaxed and distracted from thinking about their respiration, no premotor cerebral potentials preceding inspiration could be detected. This failure was not due to the slow rate of rise of inspiratory activity during quiet breathing as compared with a brisk sniff, because premotor potentials were detected when subjects intermittently generated slow active expiratory efforts. 6. These observations suggest that during quiet breathing the cerebral cortex does not contribute to respiratory drive on a breath‐by‐breath basis. Conversely, the presence of clear premotor cerebral potentials when subjects performed self‐paced inspiratory or expiratory manoeuvres illustrates the powerful cortical projection to human respiratory muscles.
A bursting potassium channel in isolated cholinergic synaptosomes of Torpedo electric organ.
Authors: Edry‐Schiller J , Ginsburg S , Rahamimoff R
Published: December 2014

1. Pinched‐off cholinergic nerve terminals (synaptosomes) prepared from the electric organ of Torpedo ocelata were fused into large structures (greater than 20 microns) using dimethyl sulphoxide and polyethylene glycol 1500, as previously described for synaptic vesicles from the same organ. 2. The giant fused synaptosomes were easily amenable to the patch clamp technique and 293 seals with a resistance greater than 4 G omega were obtained in the ‘cell‐attached’ configuration. In a large fraction of the experiments, an ‘inside‐out’ patch configuration was achieved. 3. Several types of unitary ionic currents were observed. This study describes the most frequently observed single‐channel activity which was found in 247 out of the 293 membrane patches (84.3%). 4. The single‐channel current‐voltage relation was linear between ‐60 and 20 mV and showed a slope conductance of 23.8 +/‐ 1.3 pS when the pipette contained 350‐390 mM‐Na+ and the bath facing the inside of the synaptosomal membrane contained 390 mM‐K+. 5. From extrapolated reversal potential measurements, it was concluded that this channel has a large selectivity for K+ over Na+ (70.4 +/‐ 11.5, mean +/‐ S.E.M.). Chloride ions are not transported significantly through this potassium channel. 6. This potassium channel has a low probability of opening. The probability of being in the open state increases upon depolarization and reaches about 1% when the inside of the patch is 20 mV positive compared to the pipette side. 7. The mean channel open time increases with depolarization; thus the product current x time (= charge) also increases upon depolarization, showing properties of an outward rectifier. 8. The potassium channel in the giant synaptosome membrane has a bursting behaviour. Open‐time distribution, closed‐time distribution and a Poisson analysis indicate that the minimal kinetic scheme requires one open state and three closed states.
Ca(2+)‐independent change in phosphorylation of the myosin light chain during relaxation of ferret aorta by vasodilators.
Authors: Suematsu E , Resnick M , Morgan K G
Published: December 2014

1. The effects of the vasodilators atrial natriuretic peptide (ANP) and forskolin were determined on isometric force, intracellular ionized Ca2+ concentration ([Ca2+]i) as indicated by aequorin, and myosin light chain (MLC) phosphorylation in ferret aorta. 2. Atrial natriuretic peptide (10(‐7) M) inhibited intrinsic tone with an associated significant decrease in [Ca2+]i. ANP also inhibited the contraction induced by KCl with a significant decrease in [Ca2+]i. MLC phosphorylation induced by KCl was inhibited by ANP. 3. Forskolin (10(‐6) M) decreased the intrinsic tone without significantly decreasing [Ca2+]i, although MLC phosphorylation was significantly decreased. 4. A calcium‐force curve was constructed by plotting the calibrated aequorin light signal against the resulting force. The control (potassium‐generated) calcium‐force curve was not shifted by ANP, but was significantly shifted to the right by forskolin. Forskolin also shifted the phosphorylation‐calcium curve to the right without changing the phosphorylation‐force curve. 5. We conclude that the vasodilatory effect of ANP on vascular smooth muscle is mainly due to a decrease in [Ca2+]i. On the other hand, the effect of forskolin is via both a decrease in [Ca2+]i and a change in the Ca2+ requirement for MLC phosphorylation.
The role of the beta 4‐subunit in determining the kinetic properties of rat neuronal nicotinic acetylcholine alpha 3‐receptors.
Authors: Papke R L , Heinemann S F
Published: December 2014

1. Single‐channel currents were recorded from Xenopus oocytes which had been injected with complementary RNAs (cRNAs) for the neuronal nicotinic acetylcholine receptor subunits alpha 3 and beta 4. The co‐expression of alpha 3 and beta 4 gave rise to three different channel types with conductances of 22, 18 and 13 pS. 2. The activity arising from the expression of these two subunits was compared with that observed when the alpha 3 subunit was co‐expressed with an alternative beta‐subunit, beta 2. The alpha 3 beta 4‐receptors differed from alpha 3 beta 2‐receptors in conductance, open times and most notably, in burst kinetics. The association of the beta 4‐subunit with the alpha 3‐subunit results in receptors which have a high probability of re‐opening after closing, yielding protracted bursts of activity not observed when the alpha 3‐subunit is associated with the beta 2‐subunit. 3. All three alpha 3 beta 4‐channel types had similar burst kinetics. However, the 13 pS conductance channels showed an additional long‐lived open state to varying degrees when clusters of activity within an individual record were examined.
ATP activates cationic currents and modulates the calcium current through GTP‐binding protein in rabbit portal vein.
Authors: Xiong Z L , Kitamura K , Kuriyama H
Published: December 2014

1. Effects of adenosine 5'‐triphosphate (ATP) on ionic currents of dispersed smooth muscle cells of the rabbit portal vein were investigated using the voltage‐clamp procedure. 2. ATP (greater than or equal to 300 microM) produced transient and maintained inward currents. The former was inactivated within a few seconds, but the latter lasted more than several minutes. The transient but not the maintained current was blocked by pre‐treatment with alpha,beta‐methylene adenosine 5'‐triphosphate (AMP‐CPP). The amplitude of the latter was increased by ATP in a concentration‐dependent manner. The following investigations were made on the ionic mechanism of the ATP‐induced maintained inward current. 3. In 2.5 mM‐Ca(2+)‐containing tetraethylammonium chloride (TEA‐Cl) solution (2.5 mM‐Ca(2+)‐TEA+ solution), the reversal potential for the ATP‐induced inward current was close to the Cl‐ equilibrium potential, and in 140 mM‐Na+ (nominally Ca(2+)‐free or 0.3 mM‐EGTA‐containing) solution, the reversal potential was coincident with the Na+ equilibrium potential. 4. In 2.5 mM‐Ca(2+)‐TEA+ solution but not in 140 mM‐Na+ solution and in physiological salt solution (PSS), niflumic acid (10 microM), a Cl‐ channel blocker, and Cl(‐)‐deficient perfusate in the pipette markedly inhibited the ATP‐induced inward current. These results imply that in 2.5 mM‐Ca(2+)‐TEA+ solution the ATP‐activated ion channel may admit Ca2+ which then accelerates the Ca(2+)‐dependent Cl‐ current, but in 140 mM‐Na+ solution and in PSS this channel may admit only Na+. 5. Intracellular perfusion of guanosine 5'‐O‐(3‐thio triphosphate (GTP gamma S) did not provoke the current, but significantly increased the amplitude of the ATP‐induced inward current in 2.5 mM‐Ca(2+)‐TEA+, 140 mM‐Na+ and 2.5 mM‐Ba(2+)‐containing TEA+ (2.5 mM‐Ba(2+)‐TEA+) solutions. On the other hand, intracellular perfusion of guanosine 5'‐O‐(2‐thiodiphosphate) (GDP beta S) reduced the amplitude of the ATP‐induced inward current in the above solutions. 6. A low concentration of ATP (30 microM) transiently augmented the amplitude of the voltage‐dependent Ca2+ current recorded in both 2.5 mM‐Ca(2+)‐TEA+ solution and PSS, but a high concentration of ATP (3 mM) consistently inhibited the voltage‐dependent Ca2+ current in both solutions (4 mM‐EGTA in the pipette). Such inhibition was partly prevented by application of 20 mM‐EGTA in the pipette.(ABSTRACT TRUNCATED AT 400 WORDS)
Probabilistic secretion of quanta from nerve terminals in avian ciliary ganglia modulated by adenosine.
Authors: Bennett M R , Ho S
Published: December 2014

1. The effects of adenosine on the probability of secretion of acetylcholine quanta and on presynaptic and postsynaptic action potentials was examined in the post‐hatched avian ciliary ganglion. 2. Adenosine (20 microM) reduced the average size of the excitatory postsynaptic potential (EPSP) by 33%. This was due to a decrease in quantal content of the EPSP (m). The effect was blocked by theophylline (50 microM). 3. Adenosine deaminase (2.5 i.u./ml) increased the size of the EPSP by 70%, suggesting that endogenous adenosine modulates synaptic transmission in the ciliary ganglion. However, theophylline (20‐100 microM) did not affect the EPSP in a low [Ca2+]o of 1 mM and high [Mg2+]o of 6 mM. 4. Plateau‐type action potentials with a large calcium component were generated in the ciliary neurones by bathing the ganglion in tetraethylammonium ions (TEA, 10 mM). Adenosine (20 microM) reduced the duration of these action potentials on short exposures (less than 20 min) but increased the duration on longer exposure (greater than 30 min). Adenosine did not affect the normal action potential recorded in the absence of TEA. 5. Adenosine (20 microM) hyperpolarized the nerve terminal and as a consequence increased the size of the presynaptic action potential and reduced its after‐hyperpolarization. 6. Plateau‐type action potentials with a large calcium component were generated in the nerve terminals using TEA (10 mM). The duration of these action potentials was significantly reduced by adenosine (20 microM). 7. Adenosines action on nerve terminals, to hyperpolarize the membrane and reduce calcium influx, may contribute to its effect in reducing m of the EPSP.
Comparison of the serotonin‐sensitive and Ca(2+)‐activated K+ channels in Aplysia sensory neurons.
Authors: Shuster M J , Camardo J S , Siegelbaum S A
Published: December 2014

1. Single potassium channel currents were recorded in cell‐attached and cell‐free patches from Aplysia sensory neurons. Two prominent classes of K+ channels were identified that have similar single‐channel current amplitude at 0 mV: (1) the resting conductance serotonin‐sensitive K+ channels (S‐channels) previously described in these neurons; and (2) a calcium‐activated K+ channel. A series of experiments were carried out which enable these channels to be distinguished on the basis of their biophysical properties. These experiments also provide further insight into the gating and ionic selectivity of the S‐channel. 2. In inside‐out patches, single calcium‐activated K+ channel currents (IK,Ca) show a linear i‐V curve with a slope conductance of 66 pS (normal sea water outside, 360 mM‐KCl inside) whereas single S‐channels display an outwardly rectifying i‐V curve with a slope conductance of 90 pS at 0 mV. 3. The gating of IK,Ca has a steep voltage dependence, with open probability showing an e‐fold increase for a 16 mV depolarization. Increasing internal calcium concentration from 0.2 to 10 microM shifts the activation curve by 60 mV in the hyperpolarizing direction. 4. S‐channel gating is independent of internal calcium (from less than 10 nM up to 100 microM). Steady‐state open probability of the S‐channel generally shows a weak dependence on membrane potential, with open probability increasing twofold for a 30‐100 mV depolarization. Occasional patches were observed with S‐channels displaying a much greater voltage sensitivity, with open probability increasing e‐fold for a 16‐20 mV depolarization. 5. S‐channels are selective for K+ over Na+. The selectivity ratio depends on the ratio of Na+ to K+ concentration on the same side of the membrane. Increasing K+ concentration appears to increase relative Na+ permeability, suggesting ion‐ion interactions within the channel. 6. We conclude that Aplysia sensory neurons contain two prominent distinguishable classes of K+ channels, the Ca(2+)‐independent S‐channel and a Ca(2+)‐activated channel. The gating properties of the S‐channels allow them to contribute outward repolarizing current over a wide range of membrane potentials so that their modulation by neurotransmitters contributes to changes in both resting potential and action potential duration.
Morphology of long‐term denervated rat soleus muscle and the effect of chronic electrical stimulation.
Authors: Schmalbruch H , al‐Amood W S , Lewis D M
Published: December 2014

1. Rat soleus muscles were denervated for 6‐10 months; some of these were chronically stimulated for the last 3‐8 weeks before recording. The muscles were fixed at physiological lengths and embedded in epoxy resin. 2. Sections for light microscopy were stained with p‐phenylenediamine. Denervation reduced the mean cross‐sectional area of fibres to 3% of controls (peak at 20 microns2). The cross‐sectional areas of the stimulated fibres had a peak at 70 microns 2. In light micrographs of denervated muscles, the total number of fibres appeared to be reduced; however not all fibres could be identified (see paragraph (3)). 3. In the electron microscope, many fibres showed disarrayed myofilaments. Few fibres had more or less normal cross‐striations. Muscle fibres as small as 1 micron in diameter were seen. The smallest fibres did not contain myofilaments. Some unequivocally necrotic fibres were seen. 4. Most stimulated denervated fibres showed an almost normal sarcomere pattern. Scattered throughout the muscle were single fibres as small as 2 microns in diameter, but these were well organized and could be recognized in the light microscope. Few fibres were necrotic. Often fibres were serially arranged. Satellite cells were prominent. 5. It is concluded that in long‐term denervated rat soleus the original fibres are lost and those seen are the result of repeated cycles of regeneration and necrosis. Stimulation maintains the sarcomeres and probably prevents secondary degeneration and necrosis.
Horizontal interactions between visual cortical neurones studied by cross‐correlation analysis in the cat.
Authors: Hata Y , Tsumoto T , Sato H , Tamura H
Published: December 2014

1. To explore the functional significance of horizontal neural connections in the extent of a ‘hypercolumn’ of the cat visual cortex, we carried out cross‐correlation analysis of spike trains recorded simultaneously from a pair of neurones separated horizontally by less than 1 mm. 2. Significantly correlated firings, which were found in sixty‐eight pairs of cells among 327 pairs analysed, were classified into three types on the basis of their functional implications: (1) excitatory interactions, (2) inhibitory interactions and (3) common inputs to both neurones of a pair from other sources. 3. Of these three types, common inputs were encountered most frequently. Excitatory interactions were always accompanied by common inputs. Inhibitory interactions were observed least frequently. 4. The proportion of cell pairs with correlated firings was high in pairs with a horizontal separation of less than 200 microns and decreased markedly with a horizontal separation of more than 400 microns. 5. Regarding laminar locations of cells, common inputs and excitatory interactions were often observed in layers II + III and V, whereas laminar bias was not seen in inhibitory interactions. 6. With respect to difference in orientation preference between two cells, all the three types of correlations were observed, mostly in cell pairs with a difference of less than 45 deg. In particular, common inputs and excitatory interactions were often seen in cell pairs with matched orientation preferences, but inhibitory interactions were found mostly in those with slightly different orientation preferences. In addition, common inputs and excitatory interactions tended to be found between cells with the same eye preference. 7. These results suggest that horizontal functional interactions exist mainly in a range of up to 400 microns as far as the extent of a hypercolumn of the visual cortex is concerned, and these interactions operate effectively between cortical cells with similar receptive field properties except for inhibitory interactions.
The distribution of static gamma‐axons in the tenuissimus muscle of the cat.
Authors: Banks R W
Published: December 2014

1. The distribution of static gamma‐axons within and among muscle spindles of the tenuissimus muscle has been studied in the anaesthetized cat, on the basis of the effects on the responses of primary endings when bag2 or chain fibres or both are activated by static gamma‐stimulation. 2. Locations of spindles were marked for subsequent histological analysis using teased, silver‐impregnated preparations. 3. Static effects were classified into: (i) biassing; (ii) driving; or (iii) indeterminate categories. 4. Critical correlations established that the biassing type was produced by bag2 activity, either alone or in combination with chain fibres, whereas the driving type was produced by chain fibres active alone. Indirect evidence suggested that indeterminate effects were produced by bag2 and chain fibres active together. 5. The static gamma‐axons showed some differential distribution according to their conduction velocities: faster‐conducting axons were likely to be more widely distributed among spindles but less likely to innervate chain fibres alone than were more slowly conducting axons. 6. The results are discussed in terms of their possible functional and developmental significance.
Muscarinic receptor hyperpolarizes cochlear hair cells of chick by activating Ca(2+)‐activated K+ channels.
Authors: Shigemoto T , Ohmori H
Published: December 2014

1. Electrical responses to extracellularly applied acetylcholine (ACh) and to intracellularly introduced substances were studied in isolated short and tall hair cells from the chick cochlear organ by a whole‐cell voltage clamp technique using a patch electrode. These cells were isolated without using proteolytic enzymes. 2. Short hair cells generated a transient outward current at ‐50 mV in normal saline in response to puff‐applied 100 microM‐ACh, when the patch electrode was filled with a 160 mM‐K+ and 100 microM‐EGTA‐based intracellular medium. The amplitude was 317.1 +/‐ 97.1 pA (n = 32). When ACh was applied ionophoretically, the outward current was generated with a delay of about 10 ms. 3. The amplitude of ACh‐induced current was dose dependent with a KD of 19 microM and a Hill coefficient of 1.6 when measured at ‐50 mV. 4. The ACh (100 microM)‐induced current was suppressed by 1 microM‐atropine. ACh‐induced current was generated in a Ca(2+)‐free extracellular medium; however, the second ACh puff in the Ca(2+)‐free medium generated a much reduced response. ACh‐induced current was suppressed reversibly by 100 microM‐quinine. 5. Intracellular injections of guanosine‐5'‐O‐(3‐thiotriphosphate) (GTP gamma S), inositol 1,4,5‐trisphosphate (IP3) or Ca2+ (1 microM) via the patch pipette activated outward currents at ‐50 mV. 6. When the internal medium with strong Ca(2+)‐buffering capacity (5 mM‐EGTA) was used, the ACh‐induced current was reduced to 39.3 +/‐ 6.8 pA (n = 4) at ‐50 mV (12.3% of the response in the low‐EGTA medium). 7. The reversal potential of the ACh‐induced current was ‐85.7 +/‐ 4.2 mV (n = 3) in normal saline containing 5 mM‐K+. The reversal potential was dependent on the extracellular K+ concentration ([K+]o) and was shifted 57 mV by a 10‐fold increase in [K+]o at room temperature (20‐25 degrees C). 8. These results (points 4‐7) indicate that ACh induces a K+ conductance by releasing Ca2+ intracellularly, probably by activating the pathway of muscarine receptor, G‐protein and IP3. 9. Channel activities were recorded using cell‐attached patch electrodes. Channel activities were rarely observed when ACh was applied to the extra‐patch membrane, while robust channel activities were observed when ACh was included in the patch pipette medium. It is therefore suggested that Ca(2+)‐activated K+ channels exist in the membrane in close vicinity to muscarinic receptor molecules and intracellular Ca2+ release sites.(ABSTRACT TRUNCATED AT 400 WORDS)
Heterogeneity in the effects of membrane potentials on pantothenate and glucose uptakes by rabbit renal apical membranes.
Authors: Barbarat B , Chambrey R , Podevin R A
Published: December 2014

1. Previous studies using renal brush‐border membrane vesicles have established that both the pantothenate and the low Km (Michaelis‐Menten constant), low Vmax (maximal rate) D‐glucose systems have a stoichiometry of 2 Na+: 1 organic molecule. In this study, we compared the mechanisms by which the membrane potential energizes pantothenate and D‐glucose uptakes by brush‐border membrane vesicles isolated from the whole cortex of rabbit kidney. 2. In the absence of Na+, varying the membrane potential from +60 to ‐60 mV decreased pantothenate uptake, whereas D‐glucose uptake was increased in a linear manner. These results suggested the existence of a conductive pathway for pantothenate in these membranes. They also suggested that the pantothenate free carrier is electroneutral, while the glucose free carrier is negatively charged. 3. In the presence of an inwardly directed Na+ gradient, varying the membrane potential from +60 to ‐60 mV increased Na(+)‐dependent pantothenate influx linearly. In contrast, a shift from +60 to +40 mV in the membrane potential had no influence on Na(+)‐dependent D‐glucose influx, whereas influx was a linear function of the membrane potential from +40 to ‐60 mV, indicating that there is a threshold membrane potential required for membrane potential‐dependent D‐glucose movement to occur. 4. Kinetic studies revealed that the effect of membrane potential on pantothenate uptake is through changes in the Km, while Vmax was unchanged. On the other hand, the membrane potential exerted its effect on D‐glucose transport solely on the Vmax. 5. Finally, binding studies revealed that membrane potential, both in the presence and absence of a Na+ gradient, elicited effects on phlorizin binding qualitatively similar to those observed for D‐glucose transport. 6. Implications of these findings for tubular regulation of these electrogenic secondary active transport systems are discussed.
The effects of muscarine and adrenaline on patch‐clamped frog cardiac parasympathetic neurones.
Authors: Selyanko A A , Zidichouski J A , Smith P A
Published: December 2014

1. The whole‐cell patch‐clamp technique was used to record membrane currents from neurones which were acutely dissociated from the intra‐atrial parasympathetic ganglia of Rana pipiens. The effects of muscarine and adrenaline were observed at a holding potential of ‐30 mV. Extracellular potassium concentration ([K+]o) was 2, 6 or 20 mM. 2. Muscarine (10 microM) produced inward current in thirteen cells, outward current in eighteen cells and seven cells were unaffected. Inward currents were observed in six out of ten neurones in which the intracellular solution contained adenosine triphosphate (ATP; 100 microM) and outward currents were seen in eleven out of fourteen neurones which contained adenosine 3',5'‐cyclic monophosphate (cyclic AMP; 100 microM). 3. In five out of nine cells tested, the inward current produced by muscarine was attributable to a 30% depression of a voltage‐dependent current which resembled the M‐current (IM). Muscarine‐induced inward current in the other four cells involved a steady‐state conductance increase that reached a null potential at ‐10 mV. Modest IM suppression also contributed to the response in three of these four cells. 4. Adrenaline (10 or 100 microM) produced inward currents in twelve cells, outward current in ten cells and three cells were unaffected. Outward currents were only seen in cells which contained ATP or cyclic AMP (ten out of sixteen cells) whereas inward currents were seen in eight out of nine cells which did not contain adenosine nucleotides. These inward currents were always attributable to IM suppression. 5. The outward currents induced by muscarine and adrenaline resulted from an increase in a potassium conductance (GK) that exhibited inward rectification.
Voltage‐dependent block by magnesium of neuronal nicotinic acetylcholine receptor channels in rat phaeochromocytoma cells.
Authors: Ifune C K , Steinbach J H
Published: December 2014

1. The effects of Mg2+ on the single‐channel conductance of neuronal nicotinic acetylcholine receptors were examined using receptors expressed by the rat phaeochromocytoma cell line, PC12. PC12 cells express at least three conductance classes of channels that are activated by acetylcholine, the largest conductance class being the most prevalent. This receptor channel is blocked by intracellular and extracellular Mg2+. 2. The effects of Mg2+ are asymmetrical; at a given concentration, internal Mg2+ is more effective at blocking outward currents than external Mg2+ is at blocking inward currents. Receptor channels are blocked at concentrations of Mg2+ that are low compared to the concentration of the main permeant cation, Na+, and the block is voltage dependent. 3. The block by Mg2+ is not complete as Mg2+ can permeate the channel. With 80 mM‐extracellular Mg2+ (no extracellular Na+), the channel has an inward slope conductance of 2.9 pS. 4. The block by extracellular Mg2+ can be described by a one site, two barrier model for the channel which includes a negative surface charge on the external surface of the membrane. The parameters of the model place the binding site for Mg2+ at 52% of the membrane field from the outside with an apparent dissociation constant of 14 mM. However, the same parameters cannot describe the block by intracellular Mg2+. The deviations from the model suggest that the receptor channel may have more than one binding site for Mg2+.
Mechanical and morphological properties of chronically inactive cat tibialis anterior motor units.
Authors: Pierotti D J , Roy R R , Bodine‐Fowler S C , Hodgson J A , Edgerton V R
Published: December 2014

1. The lumbar spinal cord was functionally isolated in ten cats by cord transection at the junctions of segments T12‐T13 and L7‐S1 and cutting bilaterally all dorsal roots between the two transections. Two 24 h EMG recording sessions were used to verify that muscles in the lower limb were virtually electrically silent. The cats were maintained in excellent health for 6 months. 2. Six months after spinal cord isolation, an acute experiment was performed to isolate a single motor unit from the tibialis anterior of each hindlimb using ventral root splitting techniques. Each motor unit was characterized physiologically as either fast fatigable (FF, n = 11), fast fatigue resistant (FR, n = 4), fast intermediate (FI, n = 2), or slow (S, n = 1), and repetitively stimulated to deplete the motor unit of its glycogen. 3. Maximum tensions of the fast motor units were lower than mean maximum tensions of control, whereas the S motor unit remained within the range observed in controls. In general, the isometric contractile properties, as well as fatigability, were within the ranges for each of the motor unit types in control cats. The mean fibre cross‐sectional areas of the fibres within the FR and FF motor units were approximately 40 and 50% smaller than control, while the mean fibre size of the fibers within the S motor unit was similar to control. 4. Innervation ratios and specific tensions for all experimental motor units were within the ranges of those reported for tibialis anterior motor units in control cats. Thus, it appears that the decrease in maximum tension of the fast motor units was primarily related to a reduction in fibre size. 5. The spatial distribution of the fibres within fast motor units of a spinally isolated cat, as measured by interfibre distances of the motor unit fibres, was similar to that reported for control tibialis anterior motor units. 6. These data suggest that factors independent of activity play a prominent, if not dominant, role in maintaining the complement of motor unit types typical of adult cat muscles. In addition, normal innervation patterns appear to be maintained in the absence of activity.
The importance of competition between motoneurones in developing rat muscle; effects of partial denervation at birth.
Authors: Gates H J , Ridge R M
Published: December 2014

1. The number of motor units in developing fourth deep lumbrical muscles was reduced by unilateral partial denervation of the muscle at birth, by cutting the lateral plantar nerve. A minority of the motor axons arrive via the sural nerve, and were thus not cut. Those muscles that contained one motor unit (one‐unit muscles) after partial denervation developed in the absence of competition between motoneurones. Muscles with two motor units had little competition. A few four‐unit muscles were studied for comparison. 2. Isometric twitch and tetanic tensions of single motor units were recorded in vitro at 60 days of age in response to stimulation of the sural nerve. On average, units in partially denervated muscles generated more tension than normal units. The isometric tension characteristics of the units in the one‐unit and two‐unit muscles were different from the normal units (e.g. slower contracting and more fatiguable). The units of four‐unit muscles had properties similar to those of normal muscles. 3. Fibres of an individual unit were identified by glycogen depletion and S (slow) fibres were identified in cross‐section that bound a polyclonal antibody to slow type I myosin. Those fibres that did not bind the antibody were designated F fibres. The units of one‐unit muscles had the same total number of fibres and fibre type composition (both S and F fibres in the same unit) as estimated from previous work to exist at birth. The units of two‐unit muscles contained the same total number of fibres, but apparently fewer S fibres, though this may have been as a result of incomplete glycogen depletion of some fibres. 4. It is concluded that competition between motoneurone terminals is necessary for the withdrawal of mismatched connections on muscle fibres present at birth; or, alternatively, that such withdrawal cannot take place if it would result in denervation of the muscle fibre.
Pursuit of intermittently illuminated moving targets in the human.
Authors: Barnes G R , Asselman P T
Published: December 2014

1. Experiments have been conducted in order to establish the changes in oculomotor activity which take place when the human subject attempts to pursue an intermittently illuminated moving target. 2. In an initial experiment, target motion in the horizontal plane was composed of one or two sinusoids at frequencies between 0.11 and 0.2 Hz. The target was illuminated for varying durations (10‐320 ms) at intervals between 40 and 960 ms. As pulse interval was increased or pulse duration was decreased there was a progressive increase in eye velocity gain for the smooth component of eye movement. Some smooth eye movement was generated even when the pulse interval was as large as 960 ms. 3. In a second experiment target motion consisted of a triangular waveform in which target presentation was timed to occur at regular intervals throughout each cycle. Overlaying and averaging the response from several cycles revealed a regular pattern of pulsatile activity associated with each target presentation. This response, which was particularly evident when the pulse interval was greater than 1 s, consisted of an initial build‐up of smooth eye velocity followed by an exponential decay with a time constant of 0.5‐2 s. When the pulse interval was less than 1 s there was a summation of the transient responses so that eye movement appeared quite smooth when pulse interval was reduced to 320 ms. 4. The pulsatile nature of the response was accentuated when the target was made to execute a staircase‐ramp waveform in which the target was illuminated only during the ramp component. The elimination of position change between ramps and the ability to achieve higher target velocity led to clear evidence of the summation of transient oculomotor responses. 5. The summated effects, however, were not simply attributable to the addition of responses to individual target presentations as indicated by the timing of each response. The eye velocity pulse was frequently initiated 200‐300 ms prior to target appearance, and well before the time (100 ms) at which visual feedback would be expected to become effective. 6. The effect of target step displacement alone was investigated by examination of the smooth eye movement initiated by varying numbers of steps in the waveform. This showed that the basic step response had a peak velocity of no more than 8‐10 deg/s in most individuals.(ABSTRACT TRUNCATED AT 400 WORDS)
Acetylcholine and kinin augmentation of Cl‐ secretion stimulated by prostaglandin in a canine renal epithelial cell line.
Authors: Simmons N L
Published: December 2014

1. The actions of kinins and of acetylcholine upon transepithelial ion transport in a renal‐derived cultured epithelium (Madin‐Darby canine kidney cells, MDCK) have been investigated. 2. In voltage‐clamped epithelial layers mounted in Ussing chambers and with prior stimulation of inward short‐circuit current (SCC) by 5 or 10 microM‐prostaglandin E1 (PGE1), both bradykinin (1 microM) and acetylcholine (0.1 mM) stimulate an additional, but transient, inward SCC. In the absence of PGE1 minimal effects of both bradykinin and acetylcholine upon SCC are observed. The SCC response to bradykinin and acetylcholine are attenuated with prior stimulation by 10 microM‐adrenaline. 3. Measurements of bradykinin and acetylcholine‐stimulated inward SCC with cation and anion replacement of the bathing media and the use of the Cl channel blocker 5‐nitro‐2(3‐phenylpropylamino)‐benzoic acid (NPPB) together with bumetanide to inhibit Na(+)‐K(+)‐Cl‐ ‘co‐transport’, are consistent with the bradykinin‐ and acetylcholine‐stimulated SCC being the result of basal to apical Cl‐ secretion. 4. Bradykinin (1 microM) is capable of stimulation of inward SCC from both epithelial surfaces, whilst acetylcholine is only effective from the basolateral surface. Kallidin (lys‐bradykinin) was similar in effect to bradykinin from both epithelial surfaces whereas bradykinin (1‐8) was ineffective, suggesting that B2 bradykinin receptors mediate the effect of bradykinin upon SCC. Dose‐response relationships show that the response to kallidin and bradykinin was of higher sensitivity for additions to the apical cell aspects. 5. The data are discussed in relation to a model for epithelial Cl‐ secretion, and to the mechanism of natriuresis observed with kinins and acetylcholine in vivo.
Alpha 1‐adrenergic effects on intracellular pH and calcium and on myofilaments in single rat cardiac cells.
Authors: Terzic A , Pucéat M , Clément O , Scamps F , Vassort G
Published: December 2014

1. The cellular effects of alpha 1‐adrenoceptor stimulation by phenylephrine were studied in the presence of propranolol in single cells isolated from the ventricles of rat hearts. 2. Phenylephrine (10‐100 microM) induced a biphasic pattern of inotropism in these cells: a transient negative followed by a sustained positive inotropic effect as usually observed in cardiac tissues. 3. In Snarf‐1‐loaded cells, phenylephrine induced an alkalinization. This effect was reversible on wash‐out and inhibited by prazosin, an alpha 1‐adrenoceptor antagonist. 4. The alpha 1‐adrenoceptor‐mediated increase in intracellular pH (pHi) was 0.1 pH unit in HEPES buffer containing 4.4 mM‐NaHCO3 and in Krebs buffer containing 25 mM‐NaHCO3. 5. The alkalinization was blocked by the Na(+)‐H+ antiport blocker, ethylisopropylamiloride (EIPA). 6. The recovery from an acidosis induced by a NH4Cl pre‐pulse was accelerated by phenylephrine. The phenylephrine‐induced alkalinization was attributed to activation of the Na(+)‐H+ antiport. 7. Despite its ability to increase pHi, phenylephrine did not alter Ca2+ current amplitude and kinetics. 8. Ca2+ transients recorded in Indo‐1‐loaded cells were not augmented by phenylephrine. Diastolic calcium level was decreased. 9. In single skinned cells, the Ca2+ sensitivity of the contractile proteins was increased by a pre‐treatment with phenylephrine even when the alpha 1‐adrenoceptor‐mediated alkalinizing effect had been prevented by EIPA. 10. These results lead us to propose that the alpha 1‐adrenergic‐induced positive inotropic response of heart muscle could result from an increased sensitivity of the myofilaments to Ca2+ ions. This alpha 1‐adrenoceptor‐mediated Ca2+ sensitization could result both from an intracellular alkalinization and from a direct effect on contractile proteins.
Delayed rectifier potassium channels in canine and porcine airway smooth muscle cells.
Authors: Boyle J P , Tomasic M , Kotlikoff M I
Published: December 2014

1. In order to define the ion channels underlying the inactivating, calcium‐insensitive current in airway smooth muscle cells, unitary potassium currents were recorded from canine and porcine trachealis cells, and compared with macroscopic currents. On‐cell and inside‐out single‐channel currents were compared with whole‐cell recordings made in dialysed cells. 2. Depolarizing voltage steps evoked outward unitary currents. In addition to a large conductance, calcium‐activated potassium channel (KCa), a lower conductance potassium channel was identified. This channel has a conductance of 12.7 pS (on‐cell; 1 mM‐K+ in the pipette). 3. The lower conductance channel (Kdr) was not sensitive to cytosolic Ca2+ concentration and unitary current openings occurred following a delay after the voltage step. The time course of activation of the current composed of averaged single‐channel events was very similar to that of the whole‐cell, delayed rectifier potassium current (IdK), recorded under conditions of low intracellular calcium (Kotlikoff, 1990). 4. Kdr channels also inactivated with kinetics similar to those of the macroscopic current. Averaged single‐channel records revealed a current that inactivated with kinetics that could be described by two exponentials (tau 1 = 0.14 s, tau 2 = 1.1 s; at 5 mV). These values corresponded well with previously determined values for time‐dependent inactivation of IdK. Inactivation of Kdr channels was markedly voltage dependent, and was well fitted by a Boltzmann equation with V50 = ‐53 mV; this was similar to measurements of the macroscopic current, although the V50 value was shifted to more positive potentials in whole‐cell measurements. When only the inactivating component of the macroscopic current was considered, the voltage dependence of inactivation of the single‐channel current and macroscopic current were quite similar. 5. Single‐channel kinetics indicated that Kdr channels occupy one open and two closed states. The mean open time was 1.7 ms. Inactivation results in a prominent increase in the long closed time, with little effect on the mean open time or short closed time. 6. The Kdr channel was not blocked by tetraethylammonium (TEA; 1 mM), charybdotoxin (ChTX; 100 nM) or glibenclamide (20 microM), but was blocked by 4‐aminopyridine (4‐AP; 1 mM). Similarly, 4‐AP blocked the inactivating component of the macroscopic current, but a non‐inactivating current remained. KCa currents were blocked by TEA (0.5‐1 mM) and charybdotoxin (40 nM), but were insensitive to to 4‐AP (1 mM) and glibenclamide (20 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
The central projection of electrosensory information in the platypus.
Authors: Iggo A , Gregory J E , Proske U
Published: December 2014

1. This is the first detailed description of the projection to the cerebral cortex of afferent information coming from electroreceptors in the bill of the platypus, Ornithorhynchus anatinus. 2. In animals anaesthetized with chloralose, with the bill immersed in tap water, applying a potential difference between plate electrodes on either side of the bill produced large amplitude potentials from the surface of a postero‐lateral region of cerebral cortex. Response threshold was 300 microV cm‐1, somewhat lower than threshold measured for single identified electroreceptors. Electroreceptor threshold was at least three orders of magnitude lower than threshold of mechanoreceptors to electrical stimuli (Gregory, Iggo, McIntyre & Proske, 1989a). 3. Monopolar stimulation of the bill revealed a crossed projection. The map on the cortical surface had the bill oriented dorso‐laterally, its base towards the mid‐line, the tip on the lateral edge, pointing slightly forwards. The edge of the bill faced backwards. Electrosensory information coming from the edge of the bill appeared to be much more strongly represented than input from the dorsal surface. 4. Weak electrical and mechanical stimuli applied to the bill both evoked large amplitude potentials from the same region of cortex indicating that there was complete overlap between the regions receiving tactile and electrosensory inputs. 5. Inserting microelectrodes into the deeper layers of cortex revealed burst discharges in single cells and groups of cells in response to weak electrical stimulation of the bill. Activity could be recorded over a range of depths from 0.3 to 4 mm, with the majority of responses coming from cells 1‐3 mm deep. Histological examination of lesion sites made at 1.1 mm and at 3 mm suggested that cells in the pyramidal and ganglion layers were involved in generating the activity. 6. Some evidence was obtained for interactions at the level of the cerebral cortex between activity generated by tactile and electrosensory inputs. When electrical and mechanical stimuli were both applied to the bill with an interstimulus interval of less than 25 ms, cortical neuronal responses generated by one stimulus were completely suppressed by the other. However no evidence was obtained of a direct convergence at the level of the cortex between the two modalities. 7. Cortical activity could be evoked in response to rapidly changing voltage fields. This observation, together with our earlier finding of a high rate sensitivity of the receptors, emphasizes the high dynamic sensitivity of the system. 8. It is concluded that the electrosensory system of the platypus is closely associated with the sense of touch.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of corticotrophin releasing factor in relation to the neural control of adrenal function in conscious calves.
Authors: Jones C T , Edwards A V
Published: December 2014

1. Adrenal responses to intra‐aortic infusions of pure synthetic ovine corticotrophin releasing factor (CRF), and to electrical stimulation of the preganglionic sympathetic innervation, have been investigated in functionally hypophysectomized conscious calves, in the presence and absence of a specific CRF antagonist. 2. CRF exerted a substantial steroidogenic effect on the adrenal gland of functionally hypophysectomized calves when infused intra‐aortically at a dose (1.3 ng min‐1 kg‐1) below that which caused any fall in the arterial blood pressure. This response was significantly reduced, but not abolished by a concomitant infusion of CRF‐antagonist into the aorta. 3. The steroidogenic effect of CRF was significantly reduced in the presence of exogenous adrenocorticotrophic hormone (ACTH) (2 ng min‐1 kg‐1, I.V.) and the surviving response was completely abolished by CRF‐antagonist. 4. Stimulation of the peripheral end of the splanchnic nerve at 4 Hz in functionally hypophysectomized calves given exogenous ACTH produced a rise in mean adrenal output of the same order of magnitude as did exogenous CRF under the same conditions. The response to splanchnic nerve stimulation was apparently unaffected by CRF‐antagonist although release of endogenous CRF from the gland was significantly increased thereby. 5. These results indicate that release of CRF from the adrenal gland during splanchnic nerve stimulation in the calf does not contribute significantly to the steroidogenic response thereto.