bluuebunny/crossref_metadata_2025 huggingface dataset:
Acetylcholine storage, release and leakage at the neuromuscular junction of mature adult and aged rats.
Authors: Smith D O
Published: December 2014

Acetylcholine (ACh) content, release during stimulation and spontaneous leakage were studied at the diaphragm neuromuscular junction in rats aged 10 and 28 months. In addition, quantal release statistics were determined. The results were related to the number of nerve terminals per end‐plate and to the age of the animals. Nerve terminal ACh content was lower in the 28‐month‐old rats; in nonstimulated tissue the average (+/‐ S.E.) ACh levels were 29.3 (+/‐ 4.1) and 17.2 (+/‐ 2.4) fmol per end‐plate in the 10‐ and 28‐month‐old rats, respectively. During nerve stimulation, greater amounts of ACh were released by the older rats. After 1000 impulses, the average (+/‐ S.E.) ACh release was 3.2 (+/‐ 0.2) and 3.9 (+/‐ 0.2) fmol per end‐plate in the 10‐ and the 28‐month‐old animals, respectively; however, the amounts released per nerve terminal were not significantly different. The fraction of the resting ACh content released per action potential was greater in the aged rats; this may be the cause of enhanced synaptic depression in the older animals. Leakage of ACh from cytoplasmic sources was assessed by measuring the hyperpolarization following application of d‐tubocurarine (dTC). The hyperpolarizing responses were of similar magnitude in both age groups; however, the older rats were less sensitive to ACh, indicating that cytoplasmic leakage was greater in these animals. Miniature end‐plate potentials (m.e.p.p.s) occurred twice as frequently in the aged rats; this increase could be attributed to an age‐related increase in the number of nerve terminals per end‐plate. After correcting for variations in membrane input resistance and resting potential, m.e.p.p. amplitudes were compared and found to be significantly smaller in the aged rats. Quantal release during nerve stimulation was measured and found to obey binomial statistics. Estimated values of m and n were significantly larger in the older rats; there were no age‐related differences in p. The increases in m and n could be attributed to the larger number of nerve terminals per end‐plate in the aged animals. Acetylcholinesterase (AChE) activity was assayed. In innervated tissue there were no significant differences with age; however, in non‐innervated tissue AChE activity was significantly higher in the 28‐month‐old rats.
Effect of synchronous activation of medullary inspiratory bulbo‐spinal neurones on phrenic nerve discharge in cat.
Authors: Feldman J L , McCrimmon D R , Speck D F
Published: December 2014

The effects on phrenic nerve discharge elicited by intraspinal stimulation which produced synchronous activation of bulbo‐spinal inspiratory neurones were investigated in chloralose‐urethane anaesthetized, paralysed, vagotomized and artificially ventilated cats. Descending respiratory axons were activated in the ventrolateral spinal cord at the second cervical level using either monopolar or bipolar stimulation (25‐200 microA, 100 microseconds, 1‐300 Hz). Activation of bulbo‐spinal axons was confirmed by recording both orthodromic phrenic nerve excitation and antidromic spike invasion of single, inspiratory modulated units in either the dorsal respiratory group (d.r.g.) or ventral respiratory group (v.r.g.). Antidromic activation of inspiratory bulbo‐spinal neurones was confirmed by the criteria of high frequency following and collision tests. Spinal cord stimulation at intensities of 100 microA antidromically activated approximately half of the inspiratory bulbo‐spinal neurones in the d.r.g. and v.r.g. Stimulation pulses delivered to the spinal cord elicited an orthodromic excitation of the ipsilateral phrenic nerve lasting 2‐12 ms during inspiration. The onset latency of excitation was 2‐4 ms, decreasing as inspiration progressed. Following the initial excitation there was a 4‐30 ms period of reduced phrenic nerve discharge. Continuous trains of stimuli (less than 100 microA, 100 microseconds, 1‐300 Hz) or phrenic gated trains delivered during every fourth inspiratory or expiratory cycle had little or no effect on the duration of inspiration or expiration. Brief trains (400 ms, 50 Hz, 100 microA) of bilateral spinal cord stimulation delivered at various delays from the onset of inspiration had only a transient effect on the pattern of phrenic nerve discharge, with no noticeable effect 60 ms after termination of stimulation. Based on the assumption that synchronous activation of a portion of the central pattern generator for respiration would phase shift or reset the rhythm, we conclude that the bulbo‐spinal inspiratory neurones are not responsible for generation of respiratory timing signals and play, at most, a limited role in the generation of the augmenting central inspiratory activity.
Kinetics of calcium‐dependent inactivation of calcium current in voltage‐clamped neurones of Aplysia californica.
Authors: Chad J , Eckert R , Ewald D
Published: December 2014

Ca currents flowing during voltage‐clamp depolarizations were examined in axotomized Aplysia neurones under conditions that virtually eliminated other currents. Moderate to large currents exhibited a two‐component time course of relaxation that can be approximated reasonably well by the sum of two exponentials. The rapid phase (tau 1 approximately equal to 70 ms at 0 mV) plus the slower phase (tau 2 approximately equal to 300 ms at 0 mV) ride upon a steady, non‐inactivating current, I infinity. Conditions that diminish the peak current amplitude, such as reduced stimulus depolarization, inactivation remaining from a prior depolarization, or partial blockade of the Ca conductance by Cd, slowed both phases of inactivation, and all selectively eliminated the tau 1 phase, such that weak currents exhibited only the slower phase of decline. Injection of EGTA slowed both phases of inactivation, decreased the extent of the tau 1 phase, and increased the intensity of I infinity and of the current during the tau 2 phase. For a given voltage, the rate of inactivation increased as the peak current strength was increased, and decreased as the peak current strength was decreased. For a given peak current the rate of inactivation decreased as depolarization was increased. The relation of inactivation to prior Ca2+ entry was essentially linear for small currents, but decreased in slope with time during strong currents. The relation also became shallower with increasing depolarization, suggesting an apparent decrease in the efficacy of Ca in causing inactivation at more positive potentials. The basic kinetics of Ca current inactivation along with experimentally induced changes in those kinetics were simulated with a binding‐site model in which inactivation develops during current flow as a function of the entry and accumulation of free Ca2+. This demonstrated that a single Ca‐mediated process can account for the two‐component time course of inactivation, and that the nearly bi‐exponential shape need not arise from two separate processes. The two‐component time course emerges as a consequence of a postulated hyperbolic reaction between diminishing probability of channels remaining open and the accumulation of intracellular free Ca2+. The occurrence of a single‐ or a two‐component time course of inactivation thus appears to depend on the levels of internal free Ca2+ traversed during current flow.
The central projections of carotid baroreceptors and chemoreceptors in the cat: a neurophysiological study.
Authors: Donoghue S , Felder R B , Jordan D , Spyer K M
Published: December 2014

The medullary projections of afferent neurons with cell bodies in the petrosal ganglion have been investigated using an antidromic mapping technique. Of the ninety‐three units studied, fifty‐eight were shown to have patterns of discharge indicating that they were baroreceptors and thirty‐five showed responses to stimuli indicating that they were arterial chemoreceptors. Twelve baroreceptor and thirteen chemoreceptor afferents had sufficiently stable unitary discharges to permit a detailed estimation of some of their central projections using stimulation through monopolar tungsten micro‐electrodes to evoke antidromic spikes. In order to estimate their pattern of projection, depth‐threshold contours for each penetration through the dorsomedial medulla and the values of antidromic latency were considered. Baroreceptor afferent fibres with myelinated (six units) and non‐myelinated (six units) axons showed similar patterns of central projection. All could be activated from the ipsilateral nucleus of the tractus solitarius (n.t.s.), most often from its lateral divisions rostral to the obex. The dorsolateral and dorsomedial portions of the n.t.s. were most often innervated, with the commissural subnucleus receiving an innervation in seven of the twelve neurones studied. Stimulation of the ventrolateral subnucleus was effective in activating two afferent fibres whilst stimulation of the ventral subnucleus was effective in only one case. All chemoreceptor afferent fibres had calculated conduction velocities less than 4 m/s and all were activated from the dorsomedial and medial subnuclei of the ipsilateral n.t.s. In twelve of the thirteen neurones investigated in detail there was evidence of an innervation of the commissural nucleus both at the level of the obex and behind it. In three cases this extended into the contralateral portion of the commissural nucleus. In four cases a sparse innervation of the lateral subnucleus, comprising its dorsolateral aspects, was seen. The potential significance of these distinctive patterns of projection of arterial baroreceptors and chemoreceptors is discussed in relation to cardiovascular and respiratory control.
Pharmacological evidence that adenosine triphosphate and noradrenaline are co‐transmitters in the guinea‐pig vas deferens.
Authors: Sneddon P , Westfall D P
Published: December 2014

The contractile response of the guinea‐pig vas deferens to tetanic nerve stimulation was biphasic. The first phase was mimicked by exogenously applied ATP. The second more tonic phase was mimicked by exogenously applied noradrenaline (NA). Intracellular micro‐electrodes were used to record the electrical response of the vas deferens to nerve stimulation and to exogenously applied ATP and NA. Local application of ATP (10(‐5) to 10(‐3)M), by pressure ejection from a micropipette, produced a depolarization similar in magnitude and time course to the excitatory junction potential (e.j.p.). NA produced no such response. Superfusion of the vas deferens with ATP and NA (10(‐6) to 10(‐4)M) produced a depolarization. The depolarization produced by NA was more gradual than that produced by the same concentration of ATP. The ATP‐receptor antagonist ANAPP3 (arylazido aminopropionyl‐ATP) preferentially antagonized the first component of the neurogenic contractile response and also antagonized the e.j.p. The alpha‐receptor antagonist prazosin preferentially antagonized the second phase of the neurogenic contractile response and enhanced the e.j.p. Similar results were obtained using the irreversible alpha‐receptor antagonists phenoxybenzamine and dibenamine. Cocaine (10(‐6) and 10(‐5)M) enhanced the second phase of the contractile response to nerve stimulation, but reduced the first phase. Lidocaine (10(‐5) and 10(‐4)M) had no such effect. Cocaine (10(‐6) and 10(‐5)M) reduced the magnitude of e.j.p.s. at all stimulation frequencies from 1 to 8 Hz. In the presence of the selective alpha 2‐receptor antagonist yohimbine (10(‐7)M), both phases of the contractile response to nerve stimulation were enhanced to the same degree. This concentration of yohimbine also increased the magnitude of e.j.p.s. In the presence of 10(‐7) M‐yohimbine, cocaine (10(‐6) and 10(‐5)M) still enhanced the second phase of the contractile response, but no longer reduced the initial phase of the contraction or e.j.p.s to the same degree. In vas deferens from animals pre‐treated with reserpine (2 mg/kg.day), the second phase of the contractile response to nerve stimulation was reduced but neither the first phase of the contraction nor the e.j.p.s was blocked. These results suggest that the first phase of the neurogenic contractile response of the vas deferens and the e.j.p. are mediated by ATP acting on P2‐purinoreceptors, whereas NA mediates phase two, via alpha 1‐adrenoceptors. The results also suggest that release of ATP and NA is influenced by a negative feed‐back mechanism involving presynaptic alpha 2‐adrenoceptors.
The influence of muscle respiration and glycolysis on surface and intracellular pH in fibres of the rat soleus.
Authors: de Hemptinne A , Huguenin F
Published: December 2014

Extracellular pH (pHo) and intracellular pH (pHi) of superficial fibres of the rat soleus muscle were measured in vitro using pH‐sensitive glass micro‐electrodes. The origin of the pH gradient existing between the bulk phase of extracellular solution and the surface of muscle fibres was investigated. The pHo decreased almost linearly over a distance of 285 microns from bulk solution to fibre surface. The magnitude of the bulk‐surface pH gradient is greater in the mid region of the muscle than close to the tendon. Decreasing the superfusate velocity increased the magnitude of the pH gradient. Reducing the buffer capacity of the superfusing solution had the same effect. Inhibiting the aerobic metabolism or stimulating it acidified the fibre surface. Inhibiting glycolysis alone, or both aerobic metabolism and glycolysis, alkalinized the fibre surface. Inhibiting the membrane ionic exchange process involved in pHi regulation had no effect on surface pH. Changing the rate of aerobic or anaerobic metabolism quickly modified pHi in most cases. In conclusion the bulk‐surface pH gradient seems to result mainly from diffusion of CO2 and lactic acid across an unstirred layer of fluid covering the surface of muscle fibres.
Vagal control of colonic motility in the anaesthetized ferret: evidence for a non‐cholinergic excitatory innervation.
Authors: Collman P I , Grundy D , Scratcherd T
Published: December 2014

Spontaneous colonic motility in the urethane‐anaesthetized ferret consists of two distinct types of contraction which correspond to the patterns recorded myoelectrically in conscious animals. This motility was abolished or greatly reduced when nervous conduction was prevented in the cervical vagi by cooling to below 4 degrees C. On rewarming the nerves the colonic motility returned, after a short latency, to the pre‐cool level. Atropine transiently abolished colonic motility. On its return the motility was significantly reduced but still sensitive to vagal integrity. Thus the atropine‐resistant colonic motility was also abolished or markedly reduced by cooling the cervical vagi to below 4 degrees C. On rewarming there was a longer latency for the return of motility compared to that before atropinization. Electrical vagal stimulation produced, after a short latency, large‐amplitude colonic contractions. Following atropine, the short‐latency response to electrical vagal stimulation was replaced in the majority of animals by a long‐latency response whose characteristics were quite different from those of the cholinergic response. These results are consistent with the vagus containing two functional motor pathways to the colon, one to cholinergic post‐ganglionic neurones and the other operating via a non‐cholinergic mechanism.
The effect of furosemide on sodium movements in human red blood cells.
Authors: Brand S C , Whittam R
Published: December 2014

A study has been made of Na movements in human red blood cells in order to test their sensitivity to inhibition by furosemide or bumetanide. Net changes as well as influx and efflux were measured. Unidirectional Na influx and efflux values confirmed previous evidence for components of both these fluxes sensitive to inhibition by furosemide or bumetanide. The difference between furosemide‐sensitive unidirectional influx and efflux was determined at [Na]o 140 mM and shown to be non‐significant, even when [Na]i was raised to about 45 mumol ml cells‐1. No evidence was found for an influence of furosemide on net movements of Na in cells of either slightly elevated or physiological [Na]i incubated in a 140 mM‐Na medium over 4 h. Incubation of cells, under similar conditions, for 12 h did not reveal a bumetanide‐sensitive net Na movement. The results suggest that cells with normal or slightly elevated [Na]i, incubated in media of physiological Na concentration, do not possess a mechanism sensitive to inhibition by the loop diuretics that operates to regulate cell Na.
A modulatory octopaminergic neurone increases cyclic nucleotide levels in locust skeletal muscle.
Authors: Evans P D
Published: December 2014

Octopamine increases the level of cyclic AMP in a dose‐dependent way in the locust extensor tibiae neuromuscular preparation. The response peaks after a 10 min exposure and then declines to a plateau. The effect of octopamine is potentiated in the presence of the phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine (IBMX). The levels of cyclic GMP in the muscle were not affected by octopamine. The response is stereospecific for the naturally occurring D(‐) isomer of octopamine and is also specific for monophenolic biogenic amines. Studies with a range of synthetic agonists and antagonists reveal that the receptors mediating the response are of the OCTOPAMINE2 class. Forskolin, a diterpene activator of adenylate cyclase activity, increases cyclic AMP but not cyclic GMP levels in the extensor muscle. The response has a prolonged time course and is again potentiated by IBMX. Stimulation of the octopaminergic neurone to the extensor muscle increases the levels of cyclic AMP but not those of cyclic GMP. The response is blocked by phentolamine, an alpha‐adrenergic blocking agent that also blocks the effects of octopamine in this preparation. The results are discussed in terms of the parallels between the biochemical and physiological effects of octopamine on this muscle and in terms of the mode of action of the octopamine receptors present.
Some effects of removal of external calcium on pig striated muscle.
Authors: Graf F , Schatzmann H J
Published: December 2014

Bundles of about 800 cells from the m. thyreopharyngicus of pigs were used to measure activation and inactivation during contracture by K+ depolarization. When [Ca2+] in the medium was lowered to less than 5 X 10(‐10) M for 3 min (replacing Ca2+ by Mg2+) the activation occurred at the same [K+] in the medium as in normal solution (3 mM‐Ca2+) but inactivation was shifted to lower external [K+]. The absolute value of this shift in terms of membrane potential is uncertain, because [K+] at the cell surface is unknown. Exposure for 4 min to Ca2+‐free medium (Ca2+ being replaced by Mg2+) had no effect on contractility tested after a subsequent rest of 22‐25 min in normal solution ( [Ca2+] = 2 mM). However, if the muscle underwent one maximal K+ contracture in Ca2+‐free medium the response (tetanus or K+ contracture) after the same interval in normal solution was strongly reduced, although the membrane potential recovered fully. K+ contractures in normal solution could be repeated without loss of contractile force. A K+ contracture in Ca2+‐free medium had very little effect on the response to caffeine, tested after 25 min in normal solution. It seems that Ca2+ is lost into Ca2+‐free medium only during depolarization, from a site which is not accessible to Ca2+ from outside at the resting membrane potential, or from inside at any membrane potential. This site might be located inside the transverse‐tubular membrane and, when loaded with Ca2+, might represent the positive group of the model of Chandler, Rakowski & Schneider ( 1976b ), the movement of which during depolarization activates and inactivates the Ca2+ release from the sarcoplasmic reticulum.
Facilitation at single release sites of a sympathetic neuroeffector junction in the mouse.
Authors: Blakeley A G , Mathie A , Petersen S A
Published: December 2014

Electrophysiological techniques were used to observe the release of transmitter from one or a few release sites of the sympathetic neuroeffector junction of the mouse vas deferens. Release produces transient accelerations of the depolarizing phase of the excitatory junction potential, known as 'discrete events'. Discrete events associate into families at a constant latency and peak time, but vary in amplitude between a few preferred values. As facilitation develops there is a decrease in the frequency of small members of families and an increase in the frequency of large members, a change in apparent 'quantal content'. A similar change in amplitude distribution occurs when the [Ca]o is raised. The alpha‐adrenoceptor antagonist yohimbine increases quantal content when facilitation has developed, but has no significant effect on unfacilitated discrete event amplitude unless the [Ca]o is below 2.0 mM. The alpha‐adrenoceptor agonist clonidine reduces facilitated and unfacilitated quantal content under all conditions examined.
Effects of medium acetate on cellular volume in rabbit renal cortical slices.
Authors: Cooke K R , Macknight A D
Published: December 2014

Slices of rabbit renal cortex were incubated at 25 degrees C in media in which acetate replaced chloride. There was gross cellular swelling in isosmotic 132 mM‐acetate medium, and this swelling was unique in that, with a normal medium potassium concentration, it was accompanied by a substantial increase in cellular potassium content. This accumulation of potassium, but not the cellular swelling, was dependent upon metabolism and inhibited by ouabain. This accumulation of potassium was not dependent upon the cellular swelling. It also occurred in a hyperosmotic acetate medium in which swelling was minimized. In isosmotic media, the cellular swelling was proportional to medium acetate concentration and was also affected markedly by medium pH, being greatest at an initial medium pH of 7.1 and least at pH 7.7. The swelling was reversed and cellular composition restored when tissue was re‐incubated in NaCl medium. Ouabain (10(‐3)M) largely prevented this recovery in volume. The results are consistent with plasma‐membrane‐based theories, on the assumption that membranes are much more permeable to undissociated acetic acid than they are to the acetate ion. They are inconsistent with the expectations of an alternative hypothesis (the association‐‐induction hypothesis) which ascribes the maintenance of cellular composition to properties of cellular proteins and cellular water rather than to those of the plasma membrane. The results do not favour the suggestion that cellular swelling itself results in irreversible cellular damage. The results are consistent with the hypothesis that the ouabain‐inhibitable Na‐K‐ATPase plays a major role in the regulation of cellular volume. No alternative metabolically dependent volume regulating mechanism need be postulated to explain them.
Influences of neonatal gonadectomy or androgen exposure on the sexual differentiation of the rat ventromedial hypothalamus.
Authors: Sakuma Y
Published: December 2014

Antidromic action potentials were recorded extracellularly from 830 neurones in the ventromedial hypothalamus of 137 urethane‐anaesthetized rats following electrical stimulation of the central grey matter of the mesencephalon. Antidromic spike latency (range: 1.4‐45.0 ms) and stimulus threshold (85‐1800 microA) were determined for each response in twenty‐five normal males (n = 157) and thirty females ovariectomized as adults (n = 167) as well as in thirty‐six neonatally castrated males (n = 223) and forty‐six females neonatally treated with testosterone propionate (n = 283). Frequency distribution of the antidromic spike latency was multimodal in each group of animals, and was different between the groups. Significantly more of the cells had antidromic spike latencies within two ranges of 6.0‐11.0 ms and 14.0‐20.0 ms, respectively, in the ovariectomized females than in the normal males. The proportion of cells with longer latencies was modified by testosterone administration to females or castration of males during the early post‐natal period. Neuronal populations with shorter latencies withstood endocrine manipulations. Oestrogen administration to adults significantly decreased antidromic activation thresholds in ovariectomized females and neonatally castrated males. High threshold values in the testosterone‐treated, constant oestrous females did not change after ovariectomy as adults or oestrogen supplementation. It is concluded that sexual dimorphism exists in the hypothalamic neurones shown to project to the central grey and that difference depends at least partially on neonatal endocrine treatments.
Effect of dietary carbohydrate on monosaccharide uptake by mouse small intestine in vitro.
Authors: Diamond J M , Karasov W H , Cary C , Enders D , Yung R
Published: December 2014

Using intestinal sleeves in vitro, we studied the effect of dietary carbohydrate on active monosaccharide uptake in mice. Dietary carbohydrate did not affect numerous parameters of intestinal structure, such as length, circumference, weight, protein content, villus dimensions and density, and area at the villus level. Mice on a carbohydrate‐free diet had active D‐glucose uptake relatively independent of position along the small intestine. A carbohydrate‐containing diet reversibly and within 1 day stimulated uptake except in the ileum, restoring the proximal‐to‐distal gradient in glucose uptake normally observed. This stimulation involved a 81‐116% increase in the Michaelis‐ Menton constant Vmax, and also an apparent increase in the Michaelis‐ Menton constant Km, that may however be an artifact arising from unstirred‐layer effects. Active uptake of 3‐O‐methyl‐D‐glucose also increased, permeability to glucose remained unchanged, and proline uptake reversibly decreased (probably due to the lower protein content of the carbohydrate‐containing diets). The effect of fasting on active monosaccharide uptake seemed largely due to withdrawal of dietary carbohydrate, rather than of calories per se. It is concluded that dietary carbohydrate causes induction of monosaccharide carriers in the intestine, along with its more familiar induction of pancreatic amylase and intestinal disaccharidases. Substrate‐dependent carrier induction may be physiologically significant in maintaining the proximal‐to‐distal gradient of glucose transport. An appendix presents measurements of villus area as a function of position along the intestine.
Intracellular ion activities in frog skin in relation to external sodium and effects of amiloride and/or ouabain.
Authors: Harvey B J , Kernan R P
Published: December 2014

Intracellular activities of sodium, potassium and chloride ions, aiNa, aiK, and aiCl were measured with ion‐selective single‐, double‐ and triple‐barrelled micro‐electrodes in skin and isolated epithelia of Rana temporaria bathed on both sides with normal or modified physiological saline. Apical and basolateral membrane potentials, psi ac and psi cs and resistance Ra and Rb respectively were also measured and from the latter the fractional resistance of the apical membrane, F(Ra) and voltage divider ratio, delta psi ac/delta psi cs were measured as criteria of satisfactory membrane penetration by the micro‐electrodes. Under control conditions, aiNa was 12.3 +/‐ 0.8 mM, aiK was 70.3 +/‐ 22 mM and aiCl was 20.3 +/‐ 1.6 mM with psi ac averaging ‐38.0 +/‐ 3.2 mV. When 10(‐4) M‐amiloride was added to the apical bathing fluid aiNa fell within 10 min to 1.18 +/‐ 0.1 mM and aiCl to 5.2 +/‐ 0.9 mM, while aiK increased to 86.2 +/‐ 3.8 mM as measured from the basolateral border of isolated epithelia. The sodium transport pool of the skin was measured from the fall in aiNa in the presence of amiloride and could be expressed as 33 X 10(‐9) mol cm‐2 of epithelium. The mean rate of fall of aiNa under these conditions corresponded to an efflux rate at the basolateral border of 30.1 X 10(‐9) mol cm‐2 min‐1 (48 microA cm‐2) giving a half‐time for turnover of the sodium transport pool of 33 s. Reduction of sodium concentration in the apical fluid from the normal 79 mM‐Na to 10, 1 and 0.1 mM caused aiNa to fall in stages to 2 mM. Because psi ac increased in negativity to ‐101 mV in the process, this driving force for passive sodium accumulation, more than offset the increased sodium gradient opposing sodium influx across the apical border.
The role of chloride‐bicarbonate exchange in the regulation of intracellular chloride in guinea‐pig vas deferens.
Authors: Aickin C C , Brading A F
Published: December 2014

The Cl‐depleted smooth muscle cells of guinea‐pig vas deferens rapidly restore their intracellular Cl activity ( aiCl ) to a level 5 times higher than that predicted by a passive distribution when Cl‐ ions are readmitted to the extracellular solution. Cl reaccumulation, measured using Cl‐sensitive micro‐electrodes and the uptake of 36Cl, was slowed about 3‐fold by the nominal absence of CO2 and HCO3 and about 10‐fold by the presence of the anion exchange inhibitor DIDS (4‐4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid). However, the usual level of intracellular Cl was eventually attained and neither condition reduced intracellular Cl in normal tissues. The loss of intracellular Cl that occurs when Cl‐ ions are removed from the extracellular solution was slowed about 3‐fold by the nominal absence of CO2 and HCO3 and was accelerated by their readdition. DIDS slowed the fall in aiCl about 10‐fold and reduced 36Cl efflux. Intracellular pH (pHi), measured using pH‐sensitive micro‐electrodes, increased by a mean of 0.73 units when Cl was removed from the superfusing solution in the presence of CO2 and HCO3, and rapidly decreased when Cl was readmitted. These changes are equivalent to an intracellular accumulation and loss of HCO3‐ ions respectively. The net transmembrane movement of HCO3‐ ions which would have caused these changes in pHi was calculated using the measured intracellular buffering power ( Aickin , 1984). 25% fewer HCO3‐ ions than Cl‐ ions were accumulated and lost and the HCO3 movement was completed 2‐3 times faster than the simultaneous Cl movement under the same conditions. The changes in pHi induced by alteration of extracellular Cl were reduced by the nominal absence of CO2 and HCO3 and abolished by the presence of DIDS. The acidification recorded on readmission of Cl in the nominal absence of CO2 and HCO3 was compatible with a metabolic production of about 0.1% CO2. We conclude that Cl‐HCO3 exchange plays a major role in the regulation of intracellular Cl. The exchange carrier is reversible, is completely inhibited by DIDS, and accounts for about 75% of the net Cl movement that occurs when Cl is removed from or readmitted to the extracellular solution. The mechanism which is responsible for the remaining Cl movement remains to be elucidated.
Single cardiac Purkinje cells: general electrophysiology and voltage‐clamp analysis of the pace‐maker current.
Authors: Callewaert G , Carmeliet E , Vereecke J
Published: December 2014

Single Purkinje cells from dog, sheep and cow hearts were isolated by injecting a Ca‐free collagenase containing Tyrode solution in the space between the connective tissue sheath and the Purkinje cells. A small proportion of these cells survived the isolation procedure and these cells were used for further investigation. The cells showed electrophysiological properties similar to intact Purkinje fibres as indicated by the following results. Maximum diastolic potentials between ‐70 and ‐85 mV and specific membrane resistances of 21‐32 k omega cm2 indicated that the single cells were not leaky or hyperpermeable . The action potential showed a rapid upstroke, with a maximum rate of rise, Vmax' between 150 and 750 V/s, and two phases of fast repolarization separated by a plateau phase with a duration of about 200 ms. Each action potential was followed by a spontaneous depolarization with an amplitude between 1 and 10 mV. The upstroke of the action potential could be blocked by tetrodotoxin (TTX) in a dose‐dependent manner. The rate of depolarization of the action potential was sensitive to changes in membrane potential; the resulting S‐shaped curve showed a half‐maximum potential of ‐65 mV and a steepness of 0.46 mV‐1. The duration of the action potential was sensitive to external K concentrations, catecholamines and TTX in a way similar to intact Purkinje fibres. Both application of catecholamines and lowering the external K concentration induced spontaneous activity. The cells were used to study the ionic nature of the pace‐maker current under voltage‐clamp conditions using the two‐micro‐electrode technique. This pace‐maker current was blocked in a voltage‐dependent manner by 1 mM‐Cs, and was not affected by 1 mM‐Ba. The steady‐state activation curve was shifted in the depolarizing direction by application of adrenaline. In contrast to voltage‐clamp data obtained on the pace‐maker current of intact Purkinje fibres, the pace‐maker current in a single cell did not reverse near the presumed equilibrium potential for K ions; no reversal could be seen in the voltage range negative to ‐50 mV. These observations together with preliminary results on the Na and K dependence of the pace‐maker current are strong arguments in favour of the hypothesis that the pace‐maker current in cardiac Purkinje fibres is an inward current carried by Na and K ions and activates upon hyperpolarization.
Topographical localization in the motor cortex of the cat for somatic afferent responses and evoked movements.
Authors: Armstrong D M , Drew T
Published: December 2014

Microwires chronically implanted in the pericruciate cortex of free‐to‐move cats were used to record extracellularly from cortical neurones and to deliver intracortical stimulation. Natural stimulation of cutaneous and/or deep mechanoreceptors in limbs and trunk evoked discharges in 89% of 165 neurones, 57% of which were pyramidal tract neurones. Out of 112 cells with receptive fields on the contralateral forelimb, 41% had cutaneous fields, 29% had fields involving deep tissues and 30% were driven from both sources. Cutaneous receptive fields were much commoner than deep ones among cells with fields including the forefoot; this relationship was reversed for cells with more proximal fields. Many more cells had distal than proximal fields. The 'zones' of the forelimb (i.e. foot, wrist, elbow, shoulder) provided input to widespread and overlapping cell populations within the coronal gyrus and the lateral parts of the anterior and posterior sigmoid gyri. Despite the overlap a somatotopy existed with successively more distal limb zones represented successively further laterally in the pericruciate area. Intracortical stimulation (eleven cathodal pulses, duration 0.2 ms, frequency 330 Hz, intensity 35 microA or less) evoked flick movements of the contralateral limbs which were abolished by pyramidectomy. In the forelimb, shoulder movements were commonest and elbow, wrist and digits were represented with decreasing frequency. Both for 35 microA and for threshold stimulation the distributions of the effective electrodes revealed an overlapping somatotopy such that the wrist movements were almost restricted to the coronal gyrus and shoulder movements were most often evoked from the lateral part of the anterior sigmoid gyrus. The movement and receptive field somatotopies overlapped heavily but the former showed a distinct lateral shift relative to the latter. As a result shoulder movements were not uncommonly evoked from the coronal gyrus although the shoulder provided almost no input to cells in that area.
Hormone‐induced co‐transport with specific pharmacological properties in erythrocytes of rainbow trout, Salmo gairdneri.
Authors: Baroin A , Garcia-Romeu F , Lamarre T , Motais R
Published: December 2014

On the addition of isoprenaline to an isotonic suspension of red blood cells of rainbow trout (Salmo gairdneri), the cell volume increases. This increase in volume is the result of net uptake of Na+ and osmotically obligated water. Two different pathways are involved in the salt uptake. The minor component of Na+ entry (about 20%) corresponds to a Na+ uptake independent of Cl‐ and is inhibited by amiloride, yet is insensitive to DIDS, furosemide and niflumic acid. It could result from Na+/H+ countertransport. The major component of salt uptake is due to Na+ entry which requires Cl‐ as anion, and is electroneutral, independent of extracellular K+, sensitive to amiloride, DIDS, niflumic acid and furosemide, but insensitive to other loop diuretics such as piretanide or bumetanide. These characteristics, as well as the response of valinomycin‐treated cells to isoprenaline and some other properties (ionic selectivity, drug sensitivity) of the anion exchange system of volume‐static trout red cells, permit the definition of the nature of this Cl‐‐dependent pathway. The findings are inconsistent with the electrically silent double antiporter model (proposed in amphibian red cells by Cala, 1980) and with the co‐migration of Cl‐ with Na+ through parallel conductive pathways, but strongly suggest a symport mechanism. Striking differences, mainly pharmacological, exist between this NaCl co‐transport and the duck red blood cell Na+/K+/2Cl‐ co‐transport (Kregenow, 1977, 1978; McManus & Schmidt, 1978).
Different quantal responses within single frog neuromuscular junctions.
Authors: Bieser A , Wernig A , Zucker H
Published: December 2014

At frog neuromuscular junctions spontaneous miniature end‐plate potentials (m.e.p.p.s) were recorded from several isolated spots within single synapses. This was done by consecutively placing an extracellular glass micro‐electrode (focal electrode) at different recording sites, while the intracellular electrode remained in one place. After each set of recordings, muscles were stained to reveal both axon terminals and cholinesterase (ChE) such that the exact position of each recording site could be determined. In many nerve terminal branches a similar quantum size was found at several different spots. In other instances, however, mean quantum amplitudes varied by 10‐60% at different spots along the same terminal branches. As a control, individual spots were recorded from repeatedly after repositioning the focal electrode. In these recordings mean m.e.p.p. amplitude varied by only 5‐10%. It is concluded that quantum size within a single junction is similar at many spots, but deviates markedly at others. Correlation of this variation with the stained preparations suggested that spots where quanta significantly larger or smaller than normal were recorded were either at ChE rings or at the distal ends of nerve branches, respectively; at different nerve terminal branches within the same junction, quantum amplitudes were similar in many cases but deviated in others. The results are consistent with ultrastructural evidence that frog neuromuscular junctions are non‐homogeneous structures which undergo continual remodelling.
Properties of non‐junctional acetylcholine receptor channels on innervated muscle of Xenopus laevis.
Authors: Brehm P , Kullberg R , Moody-Corbett F
Published: December 2014

Patch‐clamp recordings of current through acetylcholine‐activated channels were made from non‐junctional membrane of innervated myotomal muscle from Xenopus laevis. Two classes of acetylcholine (ACh) receptor channels were identified on the basis of current amplitudes. Both amplitude classes exhibited current‐voltage relations which deviated from linearity as the extrapolated reversal potential was approached (‐5 to ‐12 mV). Over the range of greatest linearity the conductances of the two classes were 64 and 44 pS. Both event classes were blocked by alpha‐bungarotoxin. At the normal resting membrane potential (approximately ‐95 mV) the larger conductance channel (gamma) exhibited an apparent mean channel open time of less than 1 ms, compared to approximately 2 ms for the smaller gamma class. The apparent open time was voltage‐dependent, changing e‐fold with a 63 mV hyperpolarization for the high gamma channel and 93 mV hyperpolarization for the low gamma channel. At low ACh concentrations (0.1‐0.3 microM) both amplitude classes exhibited bursts of successive openings separated by brief closures of less than 0.5 ms. Bursts were separated by longer closed intervals of 1 to greater than 100 ms. Closed interval histograms revealed corresponding populations of brief and long closures, indicating that at least two kinetic processes are required to describe the distribution of closed intervals. In the absence of exogenous ACh, channels were observed in an occasional patch which showed a conductance and extrapolated reversal potential similar to ACh‐activated channels. In such patches the event frequency could occasionally be altered by adjusting the negative pressure applied to the patch. The two main conductance classes of ACh activated channels were observed to coexist in most patches. However, the most frequent event observed in non‐junctional membrane of innervated muscle corresponded to the high gamma class. In this respect, the non‐junctional ACh receptors bore a greater similarity to junctional ACh receptors than to non‐junctional receptors reported for denervated muscle.
The direct inhibition of pancreatic electrolyte secretion by noradrenaline in the isolated perfused cat pancreas.
Authors: Elisha E E , Hutson D , Scratcherd T
Published: December 2014

The continuous infusion of noradrenaline into the arterial supply of the isolated saline‐perfused pancreas caused a dose‐dependent rise in perfusion pressure, a reduction in perfusion rate and an inhibition of pancreatic secretion. With increasing dose there was always a greater reduction in secretion rate than there was of perfusate flow rate. Manual reduction of the perfusion rate resulted in a reduction in secretion rate. When noradrenaline reduced the perfusate flow by 44.2 +/‐ 6.0% the secretion rate fell by 76.6 +/‐ 14.1%. Manual reduction of the perfusion flow rate by a similar amount (43.0 +/‐ 5.7%) only reduced the secretion rate by 41.4 +/‐ 7.0%. The infusion of noradrenaline, when all calcium had been removed from the perfusate, caused only a small increase in perfusion pressure with little change in the perfusion flow whilst at the same time the inhibition of electrolyte secretion was relatively unaffected. The vasomotor and secretory effects of noradrenaline were abolished by phentolamine. It is concluded that noradrenaline inhibits pancreatic electrolyte secretion by a direct action on the secretory cell and indirectly by vasoconstriction and that both these effects are mediated through the alpha‐receptor.
Some properties of excitatory junction currents recorded from submucosal arterioles of guinea‐pig ileum.
Authors: Finkel A S , Hirst G D , Van Helden D F
Published: December 2014

Excitatory junction potentials and excitatory junction currents have been recorded from short segments of arterioles taken from the submucosa of guinea‐pig small intestine. Excitatory junction currents reached their peak amplitudes by 20 ms and then decayed, with a time course that could be described by a single exponential (mean time constant of decay approximately 50 ms). The null potential for excitatory junction currents obtained by extrapolation was near 0 mV. The time course of excitatory junction currents failed to show voltage sensitivity. Spontaneous excitatory junction currents had the same time course as evoked currents; the amplitudes of spontaneous currents were less than an order of magnitude different from that of evoked currents.
The tendon of flexor pollicis longus: its effects on the muscular control of force and position at the human thumb.
Authors: Rack P M , Ross H F
Published: December 2014

Human flexor pollicis longus tendons obtained at autopsy were subjected to repeated sinusoidal stretching movements. The associated force changes were almost in phase with the movement (force led position by less than 4 degrees), and alterations in the frequency of movement between 2 and 16 Hz had little effect on them. Examination of the thumbs of formalin‐fixed cadavers demonstrated that the tendon exerts its force 7.4‐8.0 mm in front of the axis of movement of the interphalangeal joint. From a knowledge of the tendon properties and the joint anatomy, one can calculate the changes in tendon length that would accompany any force change at the joint. Equipped with this information one can re‐examine the responses to sinusoidal movements of the thumb interphalangeal joints of normal subjects. When the subject exerts a steady flexing force in which stretch reflexes play no important part, measurements of joint stiffness indicate that only a portion of the imposed movement reaches the muscle fibres. The extension of those (visco‐elastic) muscle fibres lags behind the extension of the (elastic) tendon. Stretch reflexes contribute to the mechanical resistance of muscle fibres to low frequency (3‐5 Hz) displacements, but in the presence of a compliant tendon the length of the muscle fibres does not determine the angle of the joint in any positive way. It is suggested that the compliant tendons of many thumb and finger muscles simplify the neuromuscular control of forces during gripping and handling movements.
Common noise in the firing of neighbouring ganglion cells in goldfish retina.
Authors: Ginsburg K S , Johnsen J A , Levine M W
Published: December 2014

Pairs of goldfish retinal ganglion cells with overlapping receptive fields were recorded during stimulation with repeated light flashes. Cross‐correlation histograms for 'maintained' discharge, 'on' responses, and 'off' responses were computed with a correction for the systematic responses to the stimuli; cross‐covariances were derived from these. If stimulus‐induced signals and noise combine linearly, then the cross‐covariances are independent of differences in mean firing rate. Cross‐covariances of pairs of cells with the same response polarity displayed a positive peak near zero lag; pairs with complementary responses showed a negative peak. 'On‐off' cells could generally be classified as on‐like or off‐like, based on the plateau of firing during a prolonged flash and the relative magnitudes of the on and off peak responses; the cross‐covariances of these cells were as one would predict if they were pure on‐ or off‐centre neurones. The cross‐covariances derived from the on period usually differed in magnitude from those derived in the dark (either maintained or off response). In general, cross‐covariances for off responses were nearly identical to those for the maintained discharges of the same pair, although the mean rates at off were usually quite different from the maintained. The change in magnitude of the cross‐covariances from on responses therefore appears to be a non‐linear effect of light, and not of the changes in firing rate induced by the light. Other features of the cross‐covariances were not affected by stimulation. The general shapes remained fairly constant, and the lags at which the peaks occurred were not consistently affected. We estimated the variance of the firing rate of each unit in three ways, and used two methods of portioning the variance implied by the cross‐covariances; from these estimates, we obtained an upper bound for the proportion of the variance of firing of a cell which is due to the common noise that affects both members of a pair. We found that the common influence accounts for less than 20% of the total variance. During stimulation, both the magnitude of the cross‐covariance and the variance of the rates change; however, the percentage of total variance contributed by the common noise source is constant. We conclude that light has the effect of changing the gain of the pathway after the introduction of both the common and unshared (private) noise sources but before the ganglion cell.(ABSTRACT TRUNCATED AT 400 WORDS)