bluuebunny/crossref_metadata_2025 huggingface dataset:
Acetylcholine‐evoked potassium release in the mouse pancreas.
Authors: Petersen O H , Singh J
Published: December 2014

Mouse pancreatic segments were superfused with physiological saline solutions and the K+ concentration in the effluent was measured by flame photometry. Acetylcholine (ACh) evoked a dose‐dependent and transient increase in the K+ concentration in the effluent (K+ release). The removal of calcium (Ca2+) from the superfusing solution and addition of 10(‐4) M‐EGTA (ethyleneglycol‐bis‐(beta‐amino‐ethylether)N,N'‐tetraacetic acid) caused a significant reduction in the ACh‐elicited K+ outflow. Pre‐treatment of pancreatic segments with the 'loop diuretics' (furosemide, piretanide and bumetanide; all 10(‐4) M) resulted in uptake of K+ into the tissue segments. The diuretics also caused a marked reduction in the ACh‐induced K+ release. Replacement of chloride (Cl‐) in the physiological salt solution by nitrate (NO3‐), sulphate (SO42‐) or iodide (I‐) caused K+ uptake and a significant reduction in the ACh‐evoked K+ release. However, when Cl‐ was replaced by bromide (Br‐) the response to ACh was virtually unaffected. When sodium (Na+) was replaced by lithium (Li+) ACh did not evoke K+ release but instead K+ uptake was observed. However, when Tris+ was substituted for Na+ ACh evoked a very small K+ release. Pre‐treatment of pancreatic segments with 10(‐3) M‐ouabain resulted in a marked sustained K+ release. In the continuing presence of ouabain ACh induced a further increase in K+ outflow. Pre‐treatment of the preparation with 10 mM‐tetraethyl‐ammonium (TEA) caused a small transient increase in K+ efflux, but TEA had virtually no effect on the secretagogue‐evoked changes in effluent K+ concentration. The results suggest the presence of a diuretic‐sensitive Na+‐K+‐Cl‐ co‐transport system in the mouse pancreatic acinar membrane.
Gastric tone modifies the responses to extrinsic neural stimuli in the anaesthetized ferret.
Authors: Andrews P L , Lawes I N
Published: December 2014

To determine the relation between resting intragastric pressure and neuronally evoked motility responses, the stomach of the anaesthetized ferret was inflated with two volumes within the physiological range. Vagal evoked contractions decreased as the resting pressure was increased. The decrease affected responses to high, but not low, intensity stimulation of the vagus. Vagal evoked relaxation of the stomach increased as a linear function of resting pressure. Atropine lowered the resting pressure in vagotomized ferrets but did not alter the relation between vagal evoked relaxation and resting pressure. Intra‐arterial acetylcholine evoked a contraction followed by a relaxation. The contraction was reduced at higher resting pressures but the relaxation increased. Hexamethonium had no effect on the contraction but substantially reduced the relaxation. Stimulation of the greater splanchnic nerve evoked two responses. The first, direct relaxation of the stomach (independent of cholinergic activity), bore the same relation to resting pressure as vagal evoked relaxation. The second, inhibition of vagal evoked contraction, had no relation to resting pressure. The degree of reduction in the amplitude of vagal evoked contraction by an immediately preceding vagal stimulation decreased at higher resting pressures. This was the opposite of vagal evoked relaxation. The capacity of stimulation of one cervical vagus to evoke a response as large as that from stimulation of two cervical vagi was shown to depend on the use of near‐maximal levels of stimulation. At low levels of stimulation the responses to two vagi were additive, and at the lowest levels there was facilitation. It was concluded that the effect of resting pressure on the amplitude of evoked contractions was mediated mainly by smooth muscle, although modulation of the quantities of transmitter released from nerves could play a minor part. The practical implications of manipulating resting pressure by changes in volume were discussed. In particular, the manipulation of resting pressure as a method of differentiating the mechanisms of central nervous influence on gastric motility was compared to surgical and pharmacological nerve block.
Origin and voltage dependence of asparagine‐induced depolarization in intestinal cells of Xenopus embryo.
Authors: Bergman C , Bergman J
Published: December 2014

The kinetics and voltage dependence of asparagine (Asn)‐induced depolarization in endoderm cells from Xenopus laevis embryos were analysed using current‐clamp techniques. The depolarization is assumed to reflect the activation of an amino acid membrane carrier; it is accompanied by a slight increase in membrane resistance and cannot be explained by only the electrogenic character of the Asn carrier. It is proposed that the Asn depolarization arises, at least in part, from the decrease of the permeability ratio PK/PNa indirectly associated with the Na‐coupled amino acid uptake. At room temperature (20‐23 degrees C) the Asn response develops according to a single exponential function whose time constant is correlated with the final level of depolarization. Both amplitude and rise time of the depolarization are sensitive to variations of membrane potential and changes in Asn or Na external concentrations. Lowering the temperature decreases the amplitude of the Asn depolarization and increases its rise time with a Q10 factor of two; the kinetics remain of the Michaelis‐Menten type, with a marked decrease in delta Emax and no change in Km. When the holding potential is altered by depolarizing and hyperpolarizing currents, the Asn response varies according to a bell‐shaped characteristic presenting an optimum near the normal resting level. Membrane depolarizations induced by Na/K‐pump inhibitors or high external K concentrations reduce the size of the Asn response; repolarizing the cell by current injection does not reverse the inhibitory effect of external K ions. Hyperpolarizing the membrane with a K‐free Ringer solution increases the amplitude of the Asn response. In all these cases a decrease in delta Emax accounts for the apparent voltage sensitivity of the carrier mechanism. When induced by alterations of [K]o, an additional change in Km is observed, suggesting a K/Na‐competitive inhibition of the Asn carrier. The results are discussed in terms of the amino acid carrier and passive membrane properties. It is suggested that the outward K‐electrochemical gradient contributes an additional source of energy to the Na‐dependent Asn uptake.
Characterization of choline transport at maternal and fetal interfaces of the perfused guinea‐pig placenta.
Authors: Sweiry J H , Yudilevich D L
Published: December 2014

Unidirectional influx and efflux of choline into the syncytiotrophoblast were investigated from both maternal and fetal circulations of the perfused guinea‐pig placenta by using a single‐circulation paired‐tracer (extracellular reference and test substrate) dilution technique. Cellular uptake of [3H]choline at 0.05 mM was (mean percentage +/‐ S.E. of mean, n = 14 placentae) 51 +/‐ 2 and 49 +/‐ 2, on maternal and fetal sides, respectively. Kinetics of unidirectional influx (0.05‐4.0 mM‐choline) indicated the existence of saturable and non‐saturable components on both sides: on maternal and fetal interfaces the Km (mM) values were respectively, 0.12 and 0.13, the Vmax (mumol min‐1 g‐1) values, 0.08 and 0.07 and the apparent linear transfer constants (min‐1 g‐1) 0.11 and 0.12. Efflux of [3H]choline from the placenta back into the ipsilateral circulation (backflux) was generally fast (20‐60% in 5‐6 min) and asymmetric with the fetal: maternal ratio usually above unity. Transplacental specific choline transfer in the dually perfused placenta, when observed, was small (less than 10% of the injected dose) following tracer injections in either direction based on the 5‐6 min collection of the contralateral circulation (at 0.05 mM‐choline). Placental retention of [3H]choline at the end of the 5‐6 min period was about 25% of the injected dose when the tracers were injected from either circulation. Analogues of choline such as hemicholinium‐3, thiamine, ethanolamine and N,N‐dimethylethanolamine inhibited choline unidirectional influx, whereas betaine and acetate had no effect. The absence of the normal sodium gradient (perfusate sodium was replaced by Tris or by lithium) did not inhibit choline transport. The metabolic inhibitors dinitrophenol (1.0 mM) and potassium cyanide (1.0 mM) were essentially ineffective (up to 40 min perfusion). The sulphydryl reagent N‐ethylmaleimide did not appear to inhibit the influx, in comparison with its effect on [3H]choline backflux which was greatly accelerated, resulting in a dramatic reduction in placental net uptake of the label. Our findings show that choline transport into the placenta is a rapid carrier‐mediated process occurring at both maternal and fetal sides of the trophoblast, at physiological blood concentrations. This cellular uptake is possibly related to the synthesis of acetylcholine, which is known to occur in human placental tissue. Specific transplacental transfer of choline was a very slow process under the conditions of our experiments and this contrasted with the observed fast and high uptake into the trophoblast.
The effects and interactions of angiotensin and vasopressin on the heart of unanaesthetized sheep.
Authors: Caine A C , Lumbers E R , Reid I A
Published: December 2014

The effects of infusions of angiotensin and vasopressin, in stepwise concentrations, on the cardiac baroreflex and on cardiac output were studied in seven adult unanaesthetized sheep and compared with those obtained with infusions of phenylephrine. Six animals were treated with the beta‐adrenoceptor blocking drug, propranolol (in order to inhibit the effects of the sympathetic nervous system on the heart). One animal was not treated with propranolol. In those animals in which arterial pressure increased during infusion of vasopressin, the slope of the systolic pressure‐pulse interval relation was greater than that seen when phenylephrine was used to increase arterial pressure. Compared with the cardiac response to pressor doses of phenylephrine, infusions of angiotensin were associated with a lesser degree of cardiac slowing and a lesser reduction in cardiac output. The effects of combined infusions of angiotensin and vasopressin on the cardiac baroreflex were studied. In five sheep which were infused with a pressor dose of angiotensin (1.1 microgram/min), the stimulatory effect of vasopressin (1.0 u./min) on pulse interval and its depressant effect on cardiac output were attenuated. In seven sheep infused with 0.5 u./min of vasopressin, I.V. infusion of angiotensin (0.2‐5.0 micrograms), produced a progressive decrease in pulse interval and increase in cardiac output as the dose was increased. Therefore, angiotensin can offset the cardioinhibitory effects of vasopressin. Since cardiac sympathetic activity was blocked and neither drug has any direct chronotropic effect on the heart, it would appear that these interactions between the two drugs affect the cardiac vagus either at a peripheral or central level.
Synaptic excitation of neurones in area 17 of the cat by intracortical axon collaterals of cortico‐geniculate cells.
Authors: Ferster D , Lindström S
Published: December 2014

Antidromic activation of layer 6 cortico‐geniculate cells from the lateral geniculate nucleus (l.g.n.) was used to study synaptic effects mediated by their intracortical axon collaterals. A specific stimulation procedure, earlier shown to suppress geniculo‐cortical synaptic effects and to enhance synaptic effects from layer 6 cell collaterals was employed to differentiate between inputs from the two pathways. Single cells in different cortical layers were recorded both extra‐ and intracellularly with glass micro‐electrodes. Antidromic activation of cortico‐geniculate cells at 10‐16 Hz induced massive, usually repetitive, spike discharges in almost all cells in layers 2‐5. The shortest latency for this synaptic activation (3.4‐7.5 ms) was found for simple cells in layer 4. Cells in layers 2, 3 and 5 responded with progressively longer latencies. Cortico‐geniculate cells in layer 6 were atypical in that hardly any responded with synaptic discharges to the stimulation. Intracellular recordings from layer 4 cells revealed, besides a monosynaptic excitatory post‐synaptic potential (e.p.s.p.) from geniculo‐cortical fibres, a late e.p.s.p. with a latency of 3.0‐4.2 ms. This e.p.s.p. could only be evoked from stimulation sites within the A laminae of the l.g.n. in retinotopic register with the recording site in the cortex. No corresponding potential was obtained by stimulation of the optic tract or the superior colliculus. The threshold intensity for the late e.p.s.p. in layer 4 cells was much higher than for the geniculo‐cortical e.p.s.p.s from the same stimulation sites, indicating that the effect was mediated by thin fibres. The late e.p.s.p.s increased dramatically in size with repetitive stimulation of the l.g.n. at frequencies above 7 Hz, while the geniculo‐cortical e.p.s.p.s remained unchanged. In all these properties, the late e.p.s.p.s resemble similar e.p.s.p.s evoked monosynaptically in principal cells of the l.g.n. by orthodromic activation of cortico‐geniculate fibres. Large e.p.s.p.s were evoked also in complex cells of layers 2, 3 and 5 and in simple cells of layer 6 upon antidromic stimulation of cortico‐geniculate fibres. The sample included many efferent neurones, identified as projection cells by antidromic activation from extracortical stimulation sites. The latency and behaviour of the e.p.s.p.s in these cells indicate that the effect was mediated indirectly via layer 4 cells. Presumably, the excitation travelled along an earlier identified chain of neurones, going from layer 4 to layers 2 and 3, from there to layer 5 and then to layer 6.(ABSTRACT TRUNCATED AT 400 WORDS)
Activation of acetylcholine synthesis in cat sympathetic ganglia: dependence on external choline and sodium‐pump rate.
Authors: Birks R I , Worsley K J , Birks R I
Published: December 2014

Acetylcholine synthesis in the perfused cat superior cervical ganglion is maximally activated without activation of release during a 10 min recovery in Locke solution following a 15 min period of Na‐pump inhibition by perfusion with K‐free Locke solution; choline (5 X 10(‐5) M) being present throughout. This procedure combined with the use of very high rates of perfusion flow has now permitted an examination of the roles of choline uptake and Na in the activation of synthesis. The data were analysed by analysis of variance as a basis for assessing experimental error and by Bartlett's test to assess equality of variance. Significance of differences between groups was estimated from this analysis (see Appendix). By selective omission of choline, either with or without addition of hemicholinium‐3 (HC‐3), in the K‐free or in the recovery period it was found that choline is only taken up for formation of acetylcholine in the recovery period. With the use of different concentrations of choline in the recovery period, and omission of choline in the K‐free period, it was found that the rate of acetylcholine synthesis increased with increasing choline concentration in conformity with Michaelis‐Menten kinetics. The choline concentration giving half‐maximal synthesis rate was 3.6 microM. Addition of 10(‐6) M‐HC‐3 during recovery completely abolished synthesis in the presence of 5 X 10(‐6) M‐choline, and 2.5 X 10(‐7) M‐HC‐3 reduced it by 68%. These values for choline dependence and inhibitory potency of HC‐3 are similar to those found for high affinity choline transport in brain synaptosomes, indicating that the same system operates in brain and in ganglia. In additional experiments in which choline was omitted in the K‐free period and with 5 X 10(‐5) M‐choline in the recovery fluid a reduction of external Na to 50 mM during recovery did not reduce significantly the maximal rate of acetylcholine synthesis. Further reduction to 25 nM, which would be expected to abolish the Na gradient, reduced the rate of synthesis by only 18%. The presence of 2 X 10(‐5) M‐ouabain during recovery in normal Locke solution containing 5 X 10(‐5) M‐choline abolished synthesis. It is concluded that choline uptake for acetylcholine synthesis in ganglia is via the high affinity transporter; that the transport is rate limiting for acetylcholine synthesis and; that the transport process is intimately linked to Na‐pump rate.(ABSTRACT TRUNCATED AT 400 WORDS)
Neostigmine increases the size of subunits composing the quantum of transmitter release at mouse neuromuscular junction.
Authors: Carlson C G , Kriebel M E
Published: December 2014

Miniature end‐plate potentials (m.e.p.p.s) were recorded from mouse diaphragm junctions. Noise‐to‐signal ratios were less than 1.3%. 1‐4 X 10(3) m.e.p.p.s were recorded before and after the addition of an anticholinesterase agent. M.e.p.p. amplitude distributions showed two classes of m.e.p.p.s. The mode of the bell m.e.p.p. class was ten‐twelve times that of the skew m.e.p.p. class. The amplitude distributions of the bell m.e.p.p. class showed integral peaks in the central region. The anticholinesterase agent increased the interval of the integral peaks but not the number of peaks. Experimental conditions that are necessary to demonstrate integral and stationary peaks on m.e.p.p. amplitude histograms are discussed. Data support the hypothesis that the quantum of transmitter release is composed of subunits.
Metabolic and cardiovascular effects on fetal sheep of sustained reduction of uterine blood flow.
Authors: Gu W , Jones C T , Parer J T
Published: December 2014

The effects on the fetus and placenta of graded reductions of uterine blood flow to 30‐90% of control have been studied in sheep at days 125‐143 of pregnancy. Reduction of uterine flow to 70‐90% of control had little effect upon fetal oxygenation or heart rate or blood pressure but elevated fetal plasma catecholamine concentration. Reduction of flow to 30‐50% of control depressed fetal arterial and umbilical venous PO2 but had little effect upon oxygen consumption unless the umbilical venous value fell below about 14 mmHg when it was depressed by up to 30%. Placental oxygen consumption did not fall and was therefore maintained at the expense of the fetus. Fetal arterial pressure rose by 10‐12 mmHg and heart rate fell by about 30 beats/min during the first 10‐15 min then rose above its initial value. Plasma adrenaline and noradrenaline concentrations rose progressively at a rate which increased with greater degrees of asphyxia. When uterine blood flow was reduced below one‐half of normal, net placental consumption of glucose fell and there was evidence of substantial provision of glucose and lactate from the fetus. Fetal production of lactate increased sharply and much of this appeared to be consumed by the placenta at a rate sufficient to account entirely for the deficit in net glucose consumption. The results are consistent with the hypothesis that the fetus senses even small changes in uterine blood flow that are alone insufficient to elicit significant blood gas changes. When the fall in uterine flow caused by arterial compression is relatively large, nutrient supply to the placenta is maintained at the expense of the fetus and as a result of fetal glucose and lactate production. The elevation of fetal arterial PCO2 appears to enhance fetal responses to hypoxia. The results are discussed in relation to the fetal responses to brief and prolonged reductions in uterine blood flow.
Propagating potassium and chloride conductances during activation and fertilization of the egg of the frog, Rana pipiens.
Authors: Jaffe L A , Kado R T , Muncy L
Published: December 2014

Fertilization or artificial activation of the frog egg (Rana pipiens) elicits a positive‐going shift in membrane potential which results from an opening of Cl‐ and K+ channels in the egg membrane. We examined the spatial localization of the currents produced by the opening of these channels, using large patch electrodes (tip diameters 3‐10 microns). We also used small patch electrodes (tip diameters about 1 micron) to study the single K+ channel currents. After activation, with the patch electrode at any position on the egg surface, we observed a transient current, with a main peak lasting several seconds. This activation current occurred after a variable delay of 0‐3 min following the rise of the activation potential. With 10% Ringer solution in the bath and pipette, the current was usually outward, although it sometimes had an inward component. With one patch electrode on the animal surface of the egg and another patch electrode on the vegetal surface, we observed that the activation current propagated over the egg surface. In experiments where the egg was activated by applying a hyperpolarizing pulse, the response in the animal half preceded that in the vegetal half by an average of about 1 min. The amplitude of the peak outward current was similar for animal and vegetal recordings (1‐2 mA/cm2). Tetraethylammonium (11 mM) in the patch pipette blocked most of the outward component of the activation current and revealed an underlying inward component. The inward component of the activation current was carried by Cl‐, since it could be reversed by raising the Cl‐ concentration in the pipette. The Cl‐ component of the activation current propagated over the egg surface, with timing similar to that of the total current. The average amplitude of the peak Cl‐ current was six or more times larger at the animal than the vegetal surface. Fertilization caused a current to propagate from the animal to the vegetal surface, like the current observed during activation. With a small patch electrode, single channel currents of the K+ component of the activation current could be seen. The probability that the channels were open increased at more positive potentials. The single channel conductance was estimated to be 25 pS, and the reversal potential to be ‐150 mV. Single Cl‐ channel currents have not yet been seen. Activation or fertilization of the frog egg resulted in a wave‐like opening of Cl‐ and K+ channels, which spread from the animal to the vegetal half of the egg.(ABSTRACT TRUNCATED AT 400 WORDS)
Inactivation of acetylcholine release from Torpedo synaptosomes in response to prolonged depolarizations.
Authors: Birman S , Meunier F M
Published: December 2014

The release of acetylcholine (ACh) from purely cholinergic Torpedo synaptosomes was monitored continuously using a chemiluminescent assay (Israël & Lesbats, 1981 a, b). Upon prolonged K+ depolarization in the presence of Ca2+, the release of ACh was transient and returned to a steady low level in about 3 min. Addition of the Ca2+ ionophore A23187 triggered the release again, suggesting that neither depletion of the transmitter store nor an inhibition of the release mechanism itself were involved in this phasic response, but rather an inactivation of the Ca2+ entry. The release response evoked by adding Ca2+ back after exposure of the synaptosomes to high K+ (70 mM) and low Ca2+ (0.57 mM) solution inactivates as a function of the duration of the pre‐depolarization with a two‐component time course with rapid (tau = 5.5 s) and slow phases (tau = 143 s). This response to Ca2+ addition was more strikingly reduced as the level of depolarization during pre‐treatment was increased. The inactivation was found to be dose dependent with respect to the amount of Ca2+ present during the pre‐depolarization period (conditioning Ca2+). Moreover, the presence of EGTA during pre‐treatment with high‐K+ solutions increased the response to applied Ca2+. These observations suggest that Ca2+ entry itself was responsible for this inactivation. No inactivation was found when ACh release was induced by the depolarizing agent Gramicidin D, except when external Na+ was replaced by Li+. This result indicates that part of the Ca2+ influx promoted by Gramicidin D depends on a Na+ entry, and may be mediated by the Na‐Ca exchange mechanism.
Heart rate at the onset of static exercise in man with partial neuromuscular blockade.
Authors: Secher N H
Published: December 2014

In human subjects the length of the first complete cardiac cycle after the onset of static finger or hand muscle contractions was recorded. Graded contractions as well as maximal contractions in which muscle fatigue was provoked by ischaemia were studied. Maximal finger muscle contractions were also weakened by partial neuromuscular blockade with either decamethonium or tubocurarine. The change in R‐R interval at the onset of exercise was variable and in part dependent on the length of the last R‐R interval before the onset of exercise. The largest decreases were seen when the preceding R‐R interval was long. During graded submaximal and maximal contractions a correlation was demonstrated between the change of the R‐R interval at the onset of exercise and the contraction intensity. At the onset of the weakest contractions a 3% prolongation of the R‐R interval was seen while the strongest contractions were associated with a shortening of 8%. At the onset of all maximal contractions, whether fatigued due to ischaemia or weakened by decamethonium or tubocurarine, a decrease in R‐R interval was seen independent of the force developed. When compared at the same resting R‐R interval, contractions performed with hand muscles elicited a greater shortening of R‐R interval than contractions with finger muscles. The results suggest that the initial change in heart rate at the onset of static muscle contractions is related to the voluntary effort rather than to the force developed, the state of the working muscles or to the type of muscle fibres involved. It may thus be elicited by 'cortical irradiation' rather than by a 'muscle‐heart reflex'. Its size depends on the length of the preceding R‐R interval, the intended contraction intensity and the muscle mass involved.
Evidence for the involvement of the organum vasculosum laminae terminalis in the febrile response of rabbits and rats.
Authors: Stitt J T
Published: December 2014

Control febrile responses to intravenous injections of endogenous pyrogen were determined in groups of rabbits and rats, exposed to their respective thermoneutral ambient temperatures. Discrete electrolytic lesions were placed within the confines of the organum vasculosum laminae terminalis (o.v.l.t.) of each species. The fever responses of the animals were remeasured 3 days later, and in every case there was a marked enhancement of the fevers produced, using the same doses of endogenous pyrogen that were used earlier. Similar lesions that were placed unilaterally within the preoptic anterior hypothalamic area in groups of control animals, were not effective in enhancing the febrile responses of these animals. The course of this lesion‐induced fever enhancement in rabbits was studied during the succeeding 3 week period, when it was found to return gradually towards the control levels. It is postulated that the o.v.l.t. is involved in some manner in the process whereby circulating pyrogen is translated into a febrile stimulus. Lesions posited within this region are thought to either increase the amount of pyrogen entering the o.v.l.t., or to increase the sensitivity of pyrogen receptor sites within the o.v.l.t.
Electric current flow inside perineurial sheaths of mouse motor nerves.
Authors: Mallart A
Published: December 2014

Micro‐electrodes were inserted inside the perineurial space to record external currents along the superficial nerve bundles of the triangularis sterni muscle of the mouse upon motor nerve stimulation. Two kinds of external currents were distinguished, the first circulating between neighbouring nodes of Ranvier in each fibre and the second circulating between the nodes and the motor endings. Ending‐node current was caused by differences in the time course and the amplitude of the potential change at the endings and at the nodes, which depended in turn, on differences between their respective membrane conductances. The stretch of nerve over which ending‐node current extended served to estimate that about eight to ten nodes of Ranvier supply the motor endings with depolarizing current.
Single‐channel analysis of fast transient potassium currents from rat nodose neurones.
Authors: Cooper E , Shrier A
Published: December 2014

Single channels that underlie the fast transient potassium current (IA) were recorded, using patch‐clamp techniques, from cultured sensory neurones. The open channel conductance was approximately 22 pS, and was constant over most of the physiological voltage range; single‐channel conductance decreased at more depolarized levels. Summing single‐channel currents resulted in an average current whose kinetics were similar to the macroscopic IA. The inactivation of these currents, at the potentials we studied, was fitted with a single exponential with a time constant of approximately 30 ms. For the currents evoked by large depolarizing steps (to +40 mV), the mean channel open time equals approximately 30 ms. For currents evoked at less depolarized levels (to 0 mV), the mean open time equals approximately 15 ms, half the inactivation time constant.
Synaptic block of a calcium‐activated potassium conductance in Aplysia neurones.
Authors: Kehoe J
Published: December 2014

In the preceding paper (Kehoe, 1985) it was shown that the firing of any one of three neurones (I, II, III) presynaptic to the medial cells of the pleural ganglion of Aplysia californica causes a diminution of the cholinergically controlled K conductance in those cells. Firing of the same three presynaptic neurones was shown here to cause a similar diminution in a depolarization‐induced K‐dependent conductance in the same post‐synaptic cells. The depolarization‐induced K conductance was found to disappear when Ca ions were removed from the sea water bathing the ganglion or when the cell was injected with the Ca chelator ethyleneglycol‐bis‐(beta‐aminoethylether)N,N'‐tetra‐acetic acid (EGTA). The diminution in this Ca‐activated, K‐dependent current occurred even when the presynaptic neurone was fired a few seconds after the end of the depolarizing voltage step to the post‐synaptic neurone, showing that the diminution in K conductance was not an indirect effect of a transmitter‐induced diminution in Ca influx during the depolarizing pulse. The two K conductances affected by the 'blocking neurones' could be selectively eliminated. The cholinergic conductance could be blocked by receptor‐specific cholinergic antagonists (e.g. 1 mM concentrations of phenyltrimethylammonium (PTMA), choline and tetraethylammonium (TEA]. Even at 10 mM concentrations, none of these compounds (including TEA, which is known to block certain Ca‐activated K conductances) had an effect on the depolarization‐induced, Ca‐activated K conductance studied here. This latter conductance, on the other hand, was selectively blocked by an intracellular injection of EGTA. The three blocking neurones continued to diminish the K conductance (cholinergic or depolarization induced) that remained intact under these different experimental conditions. The depolarization‐induced influx of Ca was shown to block the cholinergically controlled K conductance, but Ca was excluded as the possible mediator of the diminution in K conductance caused by the three blocking neurones. An intracellular injection of Ca ions into the medial cells was shown to activate a variety of changes in membrane conductance; in particular, two K‐conductance increases: an early, TEA‐sensitive one, and a slowly developing, TEA‐insensitive one. Both the permeant cyclic AMP analogue p‐chlorophenylthioadenosine 3',5'‐monophosphate (CPT‐cyclic AMP) and the phosphodiesterase inhibitors amino‐phylline and isobutyl‐1‐methylxanthine (IBMX) were shown to block the depolarization‐induced K conductance, and to reduce, though not eliminate, the slowly developing K conductance activated by an intracellular injection of Ca.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of sensory fibres in the rat splanchnic nerve in the regulation of adrenal medullary secretion during stress.
Authors: Khalil Z , Livett B G , Marley P D
Published: December 2014

We have studied the involvement of sensory nerves containing substance P (SP) in the modulation of stress‐induced catecholamine (CA) secretion from the sympathetic nervous system and adrenal medulla. Adrenaline and noradrenaline (NA) levels were measured in blood samples withdrawn from the inferior vena cava (i.v.c.) at 5 or 15 min intervals for periods of up to 60 min, in adult rats during stress induced by insulin or cold. Insulin stress caused a biphasic elevation of plasma CA. Previous studies from our laboratory have shown that the first phase lasting 30 min is neurogenic, and the second phase from 30 to 60 min is non‐neurogenic in mechanism. In control adult rats (with normal levels of SP in their splanchnic nerve), insulin stress caused a slow and progressive secretion of adrenaline into the circulation for the first 30 min (neurogenic phase). In the period 30‐60 min (non‐neurogenic phase) plasma adrenaline and NA levels rose at a much higher rate. In capsaicin‐pre‐treated rats (in which SP levels in the splanchnic nerve were depleted by 68%) insulin stress produced a steady increase in plasma adrenaline levels for up to 5 min similar to that in insulin‐stressed control animals; however, by 10 min the plasma adrenaline levels had fallen to basal and remained low up to 30 min. From 30 to 60 min, plasma adrenaline and NA levels rose steeply as seen with control animals. We conclude that capsaicin pre‐treatment affected the neurogenic phase but did not affect the non‐neurogenic phase. Cold stress increased the plasma adrenaline levels by a neurogenic mechanism over 30 min in control rats. In contrast, in capsaicin‐pre‐treated, cold‐stressed rats, plasma adrenaline did not increase significantly. Plasma NA levels were also significantly lowered in capsaicin‐pre‐treated, cold‐stressed rats during the neurogenic phase but NA increases were not dependent on an intact adrenal innervation. The results using both insulin stress and cold stress suggest that capsaicin‐sensitive (sensory) nerve fibres in the adrenal medulla and in sympathetic ganglia are capable of modifying the secretory responses of these tissues to stress. Results from our previous in vitro work are compatible with the view that SP may be the neuromodulator released from such sensory nerves to produce these effects. This suggests that the previously reported ability of SP to modulate nicotinic receptor function in vitro by either inhibiting the nicotinic response or protecting against nicotinic desensitization may be more than a mere pharmacological curiosity.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrical properties of the nexal membrane studied in rat ventricular cell pairs.
Authors: Weingart R
Published: December 2014

Cell pairs isolated from adult rat ventricles were used to characterize the electrical properties of the nexal membrane located between the cells. Each cell of a cell pair was connected to a suction pipette so as to enable whole‐cell recordings. A double voltage‐clamp method was employed which allowed the voltage gradient across the nexal membrane to be controlled. The current‐voltage relationship of the nexal membrane was found to be linear over a broad range of transnexal voltages ( +/‐ 50 mV). The measurements revealed a mean value for the apparent nexal membrane resistance, rn(app), of 3.4 M omega. Taking into account the contribution of an uncompensated series resistance (access resistance), the effective nexal resistance, rn(eff), amounts to 1.7 M omega, approximately. The nexal membrane resistance was found to be insensitive to the sarcolemmal membrane potential, Vm (voltage range tested: ‐90 mV to +30 mV). The nexal membrane showed no rectifying property, i.e. it allows impulse transmission in both directions equally well. The connexons of the nexal membrane exhibited no time‐dependent gating behaviour (time range investigated: 0.1‐10 s).
Effects of thallium on membrane currents at diastolic potentials in canine cardiac Purkinje strands.
Authors: Cohen I S , Mulrine N K
Published: December 2014

A two‐micro‐electrode voltage‐clamp technique was used to record membrane currents from canine cardiac Purkinje strands during hyperpolarizing steps to potentials between ‐70 and ‐150 mV in Tyrode solutions containing K+ and/or Tl+. Complete replacement of external K+ by equimolar Tl+ increases the instantaneous inwardly rectifying current. The inwardly rectifying region of the instantaneous I‐V relation is shifted to more positive potentials and its slope is increased. The diastolic time‐dependent current is reduced or reversed. Partial substitution of equimolar Tl+ for K+ reduces the diastolic time‐dependent current. The instantaneous I‐V relation is shifted inward for molar fractions of Tl+ (YTl) greater than 0.5, and is slightly more inward or unchanged for YTl less than or equal to 0.5. Addition of small amounts of Tl+ shifts the instantaneous I‐V relation inward and reduces the diastolic time‐dependent current. Addition of Tl+ in solutions containing Ba2+ to block the background inward rectifier has no effect on the instantaneous I‐V relation; the diastolic time‐dependent (pace‐maker) current is reduced. Block of the pace‐maker current by Tl+ is largely independent of potential in Ba2+ Tyrode solution. Since Tl+ has opposite effects on the pace‐maker current and the inward rectifier, these findings support other evidence that the pace‐maker current is not part of the background inward rectifier.
Distribution and properties of excitatory and inhibitory junction potentials in circular muscle of the guinea‐pig stomach.
Authors: Komori K , Suzuki H
Published: December 2014

In the presence of guanethidine (10(‐6)‐5 X 10(‐6) M), transmural nerve stimulation evoked an excitatory junction potential (e.j.p.) in the fundus region and an inhibitory junction potential (i.j.p.) in the antrum region of the circular muscle of the guinea‐pig stomach. The e.j.p. was blocked by atropine (over 2 X 10(‐7) M) while the i.j.p. was blocked by apamin (10(‐7) M) but not by adrenergic or cholinergic receptor antagonists. Therefore the i.j.p. may be non‐adrenergic and non‐cholinergic in nature. In the presence of atropine, nerve stimulation evoked the non‐adrenergic, non‐cholinergic i.j.p. in both regions of the stomach. In the antrum region, single stimuli enhanced the subsequent slow wave by 1.1‐1.3 times, in comparison with that before the stimuli, and this effect was blocked by atropine (over 2 X 10(‐7) M). The reversal potential for the e.j.p. was about ‐18 mV, while that for the i.j.p. was ‐87 mV in the atropinized fundus and ‐89 mV in the antrum region. In the fundus region, a pair of nerve stimulations with short intervals (1‐4 s) reduced (depression) and with long intervals (5‐20 s) enhanced (facilitation) the second e.j.p. or the i.j.p. After inhibition of acetylcholine esterase (AChE) by physostigmine or neostigmine, nerve stimulation evoked an enhanced e.j.p., and then produced a sustained depolarization with a duration of 3‐5 s in the fundus region, while the amplitude of slow waves after nerve stimulation was further enhanced in the antrum region. These effects of anticholinesterases were blocked by atropine. Exogenously applied acetylcholine (ACh) depolarized the smooth muscle membrane; the threshold concentration of ACh was about 1000 times higher in the antrum region (10(‐6) M) than in the fundus region (10(‐9) M). It is concluded that in the guinea‐pig stomach, regional differences in junction potentials may be due to different sensitivities of ACh receptor, and that nerve stimulation evokes a cholinergic e.j.p. in a high‐sensitivity region (fundus) and a non‐adrenergic, non‐cholinergic i.j.p. in a low‐sensitivity region (antrum).
Dynamics of strychnine block of single sodium channels in bovine chromaffin cells.
Authors: Yamamoto D
Published: December 2014

The kinetics of strychnine block of single Na channels in bovine chromaffin cells were studied using the gigohm seal, patch‐clamp technique, under the condition in which the Na current inactivation had been eliminated by treatment with N‐bromoacetamide (NBA). Strychnine, applied to the cytoplasmic face of Na channels at concentrations ranging from 25 to 100 microM, caused repetitive rapid transitions (flickering) between open and blocked states within single openings of Na channels, without affecting the amplitude of the single‐channel current. Average currents in the presence of strychnine accompanied 'hooked' tail currents upon repolarization. The histograms for blocked times and the histograms for open times could be fitted with a single‐exponential function. The mean open time (to) became shorter as the drug concentration was increased, while the mean blocked time (tb) was concentration independent. The association (blocking) rate constant, k, calculated from the slope of the curve relating the reciprocal mean open time to strychnine concentration was 7.6 X 10(6) M‐1 S‐1 at ‐40 mV in a typical experiment. to‐1 and tb‐1 had opposite voltage dependences: tb‐1 became larger as the membrane was hyperpolarized whereas to‐1 became smaller. The voltage dependence suggests that a first‐order blocking site is located 35% of the way through the membrane electric field from the cytoplasmic surface. An increase in the external Na+ concentration greatly decreased to‐1 without affecting tb‐1. The voltage dependence of both to‐1 and tb‐1 did not change when the external Na concentration was changed. It is suggested that the strychnine block of single Na channels is not 'current‐dependent'. All of the features of strychnine block of single Na channels are compatible with the sequential model, in which strychnine molecules block open Na channels, and the blocked channels could not close until strychnine molecules had left the blocking site in the channels.
Ia afferent excitation of motoneurones in the in vitro new‐born rat spinal cord is selectively antagonized by kynurenate.
Authors: Jahr C E , Yoshioka K
Published: December 2014

Intracellular recordings from motoneurones in in vitro preparations of new‐born rat spinal cord were used to study the sensitivity of the Ia excitatory post‐synaptic potential (e.p.s.p.) to antagonists of excitatory amino acids, in order to test whether group Ia primary afferents release L‐glutamate, or a similar compound, as a neurotransmitter. The Ia e.p.s.p. was isolated for study by using low intensity stimulation of individual muscle nerves and by the addition to the superfusate of high concentrations of divalent cations which suppressed polysynaptic inputs to the motoneurones. The pattern of convergence of group Ia afferents from homonymous, heteronymous and antagonist muscle nerves onto motoneurones in the new‐born rat was similar to that reported in the adult cat spinal cord. Homonymous muscle nerve stimulation evoked the largest amplitude Ia e.p.s.p.s while heteronymous muscle nerve stimulation elicited smaller e.p.s.p.s or had no effect. Stimulation of antagonist muscle nerves resulted in inhibitory post‐synaptic potentials (i.p.s.p.). Superfusion of the specific N‐methyl‐D‐aspartate (NMDA) receptor antagonist, 2‐amino‐5‐phosphonovalerate, did not inhibit the Ia e.p.s.p. but did suppress later, polysynaptic components of the response evoked from dorsal roots. Kynurenate was a potent inhibitor of the Ia e.p.s.p. The site of action of kynurenate was examined by observing its effect on synaptic depression and was found to be consistent with a post‐synaptic mechanism. Kynurenate selectively blocked the depolarization of motoneurones elicited by L‐glutamate and had no effect on the depolarization evoked by carbachol. The selectivity of action of kynurenate was further examined by comparing its effect on the recurrent i.p.s.p. evoked by ventral root stimulation with its effect on the Ia e.p.s.p. The recurrent i.p.s.p. was antagonized by strychnine and dihydro‐beta‐erythroidine while kynurenate, at a concentration which greatly reduced the Ia e.p.s.p., had no effect. These results suggest that stimulation of group Ia primary afferents evokes the release of L‐glutamate, or a similar compound, which activates non‐NMDA excitatory amino acid receptors on motoneurones which, in turn, mediate the Ia e.p.s.p.
Characteristics of neuro‐effector transmission in the smooth muscle layer of dog bronchiole and modifications by autacoids.
Authors: Inoue T , Ito Y
Published: December 2014

Electrical and mechanical properties of smooth muscle cells and of neuro‐effector transmission in the smooth muscle layer of the dog bronchiole (about 1 mm in diameter) were studied with double‐sucrose‐gap, micro‐electrode or tension recording methods. Electrical field stimulation of short duration (50 microseconds) applied to the whole tissue excited the intrinsic nerves, and evoked excitatory junction potentials (e.j.p.s) followed by a twitch‐like tension; these were abolished by tetrodotoxin (10(‐7) M) or by atropine (10(‐6) M). 5‐Hydroxytryptamine (10(‐5) M) produced a tonic contracture of the bronchiole, and electrical field stimulation applied during the tonic contracture produced an initial phasic contraction and a subsequent relaxation. Atropine (10(‐6) M) and propranolol (10(‐6) M) selectively abolished the phasic contraction and relaxation, respectively, indicating that dog bronchiolar muscles are innervated by excitatory cholinergic and inhibitory adrenergic nerve fibres. E.j.p.s and twitch contractions evoked by electrical field stimulation at 3 min intervals showed a gradual reduction in amplitude during superfusion with normal Krebs solution, and this reduction was overcome by pre‐treatment with indomethacin (10(‐5) M). The mean value of the resting membrane potential of the bronchiole smooth muscle cells was ‐70.2 +/‐ 2.2 mV (+/‐ S.D., n = 150), and an action potential was superimposed on e.j.p.s in 50% of the muscle cells examined when the amplitude of e.j.p.s exceeded 35 mV. During repetitive field stimulation at 0.1‐0.2 Hz, the amplitude of the e.j.p.s gradually increased (facilitation); this phenomenon was markedly enhanced by indomethacin (10(‐5) M) and was depressed by exogenously applied prostaglandins in low concentrations (10(‐11)‐10(‐8) M). Histamine (5 X 10(‐8)‐5 X 10(‐7) M) enhanced the amplitude of e.j.p.s and twitch contraction evoked by field stimulation, and this effect was antagonized by mepyramine (10(‐7) M). Histamine (10(‐7) M) enhanced the amplitude of the ACh‐induced contraction when a relatively low concentration (10(‐7) M) of ACh was applied, but not when concentrations of 10(‐6) M‐ or 10(‐5) M‐ACh were applied. Histamine had no effects on the facilitation of e.j.p. Bronchiolar smooth muscle cells therefore showed larger resting potentials and a greater tendency to fire action potentials than trachealis muscle, and prostaglandins and histamine are involved in inhibitory and accelerative mechanisms related to excitatory neuro‐effector transmission, respectively.