bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium current noise induced by barium ions in frog skeletal muscle.
Authors: DeCoursey T E , Hutter O F
Published: December 2014

Ba2+ was used to introduce K+ current fluctuations in addition to those arising from the intrinsic 'gating' mechanism studied in the preceding paper. In the presence of 0.5 to 2.0 mM‐Ba2+, Lorentzian spectra were observed at potentials between ‐10 and ‐63 mV. The amplitude and corner frequency of these Lorentzian spectra varied with voltage in the general manner to be expected from the voltage‐ and time‐dependent blocking action of Ba2+, but the microscopically determined time constant was consistently faster than that determined from the intensification of block upon hyperpolarization. The variance of the Ba2+‐induced fluctuations could be used to calculate the limiting single‐channel conductance, gamma, without the need to assume a specific model for inward rectification. The value of gamma obtained for preparations in symmetrical 120 mM‐K+ was about 8 pS (20‐24 degrees), in good agreement with that found in the preceding paper. Some fibres underwent a spontaneous, large increase in membrane conductance. This conductance showed inward rectification in the positive quadrant. At negative potentials this high conductance was blocked by 1 mM‐Ba2+ in a voltage‐ and time‐dependent manner. The block became faster and more complete at more negative potentials. Analysis of current noise in the high conductance state in the presence of Ba2+ gave Lorentzian spectra with corner frequencies in general agreement with the time constant of macroscopic current relaxations. The unitary conductance in that state was estimated to be at least 70 pS.
Interactions between the effects of adenosine and calcium on synaptic responses in rat hippocampus in vitro.
Authors: Dunwiddie T V
Published: December 2014

The effect of adenosine on synaptic responses in the in vitro rat hippocampus was examined. As has been previously described, adenosine had a profound depressant effect on synaptic transmission at excitatory synapses on the CA1 pyramidal cells. Although adenosine also produced small decreases in the amplitude of the presynaptic fibre spike, this was unable to account for the relatively much greater decrease in the amplitude of the extracellularly recorded field excitatory post‐synaptic potential (e.p.s.p.). The effect of the calcium concentration of the bathing medium on responses to adenosine was also examined. Adenosine generally had a greater depressant effect on field e.p.s.p.s from slices maintained in low concentrations of calcium (1 mM) than in high (10 mM‐calcium). However, at low response amplitudes, the effect of adenosine in the two kinds of medium was quite similar. When corrections were made for non‐linear summation of e.p.s.p.s, it was found that the effects of adenosine appeared to be independent of the calcium concentration of the medium. These data suggest that adenosine inhibits synaptic transmission by a calcium‐independent regulatory mechanism, and that adenosine does not interfere with calcium influx or calcium levels in the presynaptic terminal. Comparisons of dose‐response relationships in media containing different concentrations of calcium suggest that a maximal drug response can occur with less than maximal receptor occupancy at physiological calcium concentrations (less than 2.5 mM).
Redistribution of sarcomere length during isometric contraction of frog muscle fibres and its relation to tension creep.
Authors: Edman K A , Reggiani C
Published: December 2014

Changes in length of successive 0.5‐0.8 mm segments along single muscle fibres of Rana temporaria were recorded during 3 s isometric (fixed fibre ends) tetani at 2.15 and 2.60 micron sarcomere length. The measurements were performed by means of a photo‐electric detector system which recorded the distance between opaque markers (ca. 60 microns in width) that were attached to the upper surface of the fibre. The segment length change had an initial rapid phase (1) which coincided with the steep rise of force and a subsequent slow phase (2) which coincided with the upper, rounded portion of the force myogram and the 'plateau' of the tetanus. At 2.15 micron sarcomere length the majority of the central segments (comprising approximately 90% of the fibre) shortened to various degrees during phase 1. A considerable redistribution of length occurred during phase 2 in that some segments shortened at the expense of others which were forcibly stretched. The central region, taken as a whole, shortened by 0.1‐0.5% during phase 2. The end segments were consistently found to elongate during phase 1. However, they were able to hold the tension, without further elongation, during phase 2. The pattern of length changes within the central region of the fibre observed at 2.15 micron sarcomere spacing remained largely the same after increasing the sarcomere length to 2.60 micron. However, in contrast to the situation at 2.15 micron sarcomere length there was an over‐all (0.4‐1.5%) elongation of the central region of the fibre during phase 2 at the great fibre length. This elongation of the central region was associated with marked shortening of the end segments. The sarcomere length of the end segments (s.1.e) was compared to that of the central region of the fibre (s.l.c) at various fibre rest lengths. There was no significant difference between s.l.e and s.l.c when the fibre was just taut, i.e. at approximately 2.1 micron sarcomere length. The following relationship between s.l.e and s.l.c was found to apply for values of s.l.c ranging between 2.2 and 2.7 micron: s.l.e = 0.636 s.l.c + 0.744 (correlation coefficient, 0.93). The possibility was explored that redistribution of sarcomere length along the fibre causes the slow climb of force ('tension creep') that occurs during a tetanus at great (greater than 2.2 micron) sarcomere lengths. Tension creep could be reproduced, after peak force had been attained, during an isometric tetanus by releasing the fibre to shorten within the range 2.6‐2.3 micron sarcomere length.(ABSTRACT TRUNCATED AT 400 WORDS)
Slow excitatory post‐synaptic currents in bull‐frog sympathetic neurones.
Authors: Akasu T , Gallagher J P , Koketsu K , Shinnick-Gallagher P
Published: December 2014

Electrogenesis of the slow excitatory post‐synaptic current (slow e.p.s.c.) was analysed with voltage‐clamp methods in curarized sympathetic ganglion cells of bull‐frogs. Three types of slow e.p.s.c. were observed from B neurones of sympathetic ganglia. The type I slow e.p.s.c. was associated with a decrease in membrane conductance, was depressed by membrane hyperpolarization and nullified at ‐60 to ‐70 mV. It was observed in 65% of the sympathetic neurones studied. The type II slow e.p.s.c. was associated with an increase in membrane conductance, was depressed by membrane depolarization and nullified at around +5 mV. It was observed in 14% of the neurones studied. A third type of slow e.p.s.c. was recorded from 21% of the sympathetic neurones in this study. This slow e.p.s.c. was a mixed type having characteristics of both type I and type II slow e.p.s.c.s. Activation of muscarinic cholinergic receptors by application of acetylcholine (ACh) also produced two types of inward currents. The nature of each type of muscarinic slow ACh current was similar to that of each type of slow e.p.s.c. The time course of the falling phase of type I and type II slow e.p.s.c.s was dependent on the membrane potential. The type I slow e.p.s.c. was primarily dependent on extracellular K+ and appeared to be produced by a suppression of the M‐current (Brown & Adams, 1980). The type II slow e.p.s.c. was due to an increased conductance, probably to Na+, and other cations.
Active reactions of the rabbit ear artery to distension.
Authors: Speden R N
Published: December 2014

Changes in the external diameter of active arteries, excised from the rabbit ear, were recorded following jumps in pressure within the arteries. The arteries were either spontaneously active or were constricted with noradrenaline. Active arteries dilated when the transmural pressure was jumped from 60 to 100 mmHg, but the dilatation was largely, sometimes completely, overcome by compensatory constriction within 1‐2 min. Varying the constriction from 15 to 80% of the maximal constriction had no effect on the ability of the arteries to counteract distension. An average of 90 +/‐ 2% of the distension was overcome in 2 min and this was achieved against increases in stress (force/wall cross‐sectional area) on the muscle of not less than 74%. Jumps in pressure rarely enhanced constriction and then only when constriction was slight (less than 15% of maximal). Restoring the transmural pressure to 60 from 100 mmHg produced a transient constriction when the initial constriction was less than 50% of the maximal constriction. The sequence of counteraction of distension and transient constriction on reversing the pressure jump was reproducible for many hours. Increasing constriction of the arteries first decreased and then, at maximal constriction, suppressed all transient changes in diameter. Smaller jumps in pressure produced less dilatation which was more readily prevented by increasing constriction. These results show that the wall of the ear artery possesses a pressure‐sensitive, negative feed‐back mechanism which minimized changes in diameter following jumps in pressure.
Rhythmic discharge of climbing fibre afferents in response to natural peripheral stimuli in the cat.
Authors: Bloedel J R , Ebner T J
Published: December 2014

The rhythmicity of inferior olivary neurones evoked by natural ipsilateral forepaw inputs was evaluated in the climbing fibre afferent discharge of Purkinje cells recorded in the cerebellar cortex of the decerebrate, unanaesthetized cat. Almost 50% of all Purkinje cells responding to the forepaw stimulus with an increase in complex spike activity exhibited periodic discharge, with the dominant periodicity being between 100 and 160 ms. In ten of twenty‐five neighbouring, simultaneously recorded Purkinje cells the forepaw stimulus evoked similar periodicity in their complex spike discharge. For some cells two peaks of complex spike activity were evoked by a forepaw stimulus without an obvious third peak. By altering the stimulus duration the second peak of the response was shown to be temporally uncoupled to the 'off' phase of the displacement for many cells. The interdependence of the trials contributing to the periodic peaks in the peristimulus time histogram (p.s.t.h.) was examined by a 'separation technique'. This analysis indicated that the complex spikes contributing to a specific peak in the p.s.t.h. were generated with a high degree of independence (i.e. in different trials) from the complex spikes contributing to any other peak. It was hypothesized that the independence of the rhythmic complex spike peaks is due to the long relative refractoriness following a complex spike in a single cell. Therefore, the probability of a complex spike occurring at the next one or two cycles is decreased significantly. As a consequence, an inferior olivary neurone fires usually at only one of the various peaks in response to a single presentation of the forepaw stimulus. This hypothesis predicts that stimuli evoking a complex spike at the initial peak in a high percentage of trials should give rise to less periodicity. This prediction was tested by comparing the presence or absence of evoked oscillation with the probability of evoking a complex spike in the first peak of the p.s.t.h. Cells exhibiting a probability for complex spike discharge of over 50% in the first peak showed much less periodicity than cells with a complex spike occurring in less than 50% of the trials in the first peak. These results are discussed in the context of the inferior olive being viewed as a population of coupled elements with a tendency to oscillate. The natural forepaw stimulus is hypothesized as synchronizing the phases of spontaneously oscillating climbing fibre afferents, resulting in the observed periodicity in the complex spike p.s.t.h.
Turnover of acetylcholinesterase in innervated and denervated rat diaphragm.
Authors: Newman J R , Virgin J B , Younkin L H , Younkin S G
Published: December 2014

The acetylcholinesterase (AChE) in rat diaphragms was labelled by intravenous injection of echothiophate in order to evaluate the turnover of AChE in innervated and denervated muscle in vivo. Echothiophate diethylphosphorylates AChE thereby inactivating it. Labelled (diethylphosphorylated) enzyme is rapidly and quantitatively reactivated with 1‐methyl‐2‐hydroxyiminomethylpyridinium (2‐PAM), so labelled (diethylphosphorylated) AChE was conveniently measured as 2‐PAM‐reactivatable AChE activity. In homogenates in vitro, label is lost spontaneously (diethylphosphorylated AChE spontaneously reactivates) with a half‐time of 27 h. In innervated diaphragm, labelled non‐end‐plate AChE is lost with a half‐time of 13 h. When correction is made for the spontaneous loss of label on the basis of in vitro measurements, this data indicates that non‐end‐plate AChE turns over with a half‐time of about 26 h. In innervated diaphragm, labelled end‐plate‐specific AChE is lost more slowly than non‐end‐plate AChE and at a rate essentially identical to the rate of spontaneous loss of label in vitro. The rate of loss of labelled non‐end‐plate AChE is essentially identical in 18 h denervated and in paired innervated diaphragms. The rate of loss of labelled end‐plate‐specific AChE is significantly faster in 18 h denervated diaphragms than in paired innervated diaphragms. On the basis of these observations, hypotheses concerning the mechanisms of the denervation‐induced decreases in non‐end‐plate and end‐plate‐specific AChE are formulated and discussed.
Electrophysiological evidence for facilitatory control of oxytocin neurones by oxytocin during suckling in the rat.
Authors: Freund-Mercier M J , Richard P
Published: December 2014

Antidromically identified paraventricular neurones were recorded simultaneously with intramammary pressure in urethane (1.2 g/kg) anaesthetized rats during suckling. The correlation of the firing pattern of these neurones with milk ejection enabled distinction between oxytocin and vasopressin neurones. Oxytocin neurones displayed a short (2‐6 s) characteristic high‐frequency burst of spikes. This activation probably occurred simultaneously in all oxytocin neurones 12‐18 s before milk ejection and was regular in both frequency and amplitude (total number of spikes). The role of neurohypophysial peptides and analogues in the control of these characteristics was studied. Injecting 10 pg, 100 pg and 1 ng of oxytocin into the 3rd ventricle increased background activity of slow‐firing oxytocin neurones (less than 3 spikes/s) and had a strong dose‐dependent facilitatory effect on the milk ejection reflex, increasing both the amplitude and frequency of neurosecretory bursts. No effect was observed on non‐neurosecretory neurones. Such injection also triggered the milk ejection reflex when it had not appeared an hour after suckling began. Oxytocin did not itself induce neurosecretory activation, which only appeared if the young rats were sucking. Injecting oxytocin into the lateral ventricle was less effective than into the 3rd ventricle. No effect was observed after injection into the venous blood or into the 4th ventricle, which suggested that oxytocin acts in the hypothalamus. Injecting mesotocin or isotocin into the 3rd ventricle had a facilitatory effect similar to that of oxytocin but vasopressin, vasotocin, MIF I (pro‐leu‐gly‐NH2, terminal triplet oxytocin) or bovine neurophysins I and II did not modify neurosecretory activation or the milk ejection pattern. Injecting an oxytocin antagonist, ([1(beta‐mercapto‐beta, beta cyclopentamethylene propionic acid), 8‐ornithine] vasotocin, d(CH2)5OVT) into the 3rd ventricle decreased milk ejection frequency and considerably delayed the reappearance of the first milk ejection. This resulted from a decrease in both frequency and amplitude of neurosecretory bursts, which were too small to induce detectable oxytocin release. Moreover, d(CH2)5OVT suppressed the facilitatory effect of exogenous oxytocin. Under normal conditions, endogenous oxytocin seemed to be involved in the control of neurosecretory activation. Injecting 1 ng oxytocin or 1 or 10 ng vasopressin into the 3rd ventricle did not modify the firing pattern of vasopressin neurones whether activated by hyperosmotic stimulation (1 ml NaCl, 9% solution (w/v) I.P.) or not.(ABSTRACT TRUNCATED AT 400 WORDS)
Ionic basis of the hyperpolarizing action of adenyl compounds on sinus venosus of the tortoise heart.
Authors: Hutter O F , Rankin A C
Published: December 2014

The ionic mechanism underlying the hyperpolarizing action of adenosine and adenine nucleotides was studied by measuring the efflux of 43K or 86Rb from sinus venosus and interauricular septum of tortoise heart. Preparations rendered quiescent by high‐K (27 mM) Ringer solution were used. Adenosine and ATP increased the efflux of 43K and 86Rb from sinus venosus. The magnitude of the responses varied from preparation to preparation, but in the same tissue adenosine and ATP were of equal efficacy. When dose‐response relationships could be determined, the adenyl compounds were found to be of similar potency. Km for adenosine was 6.2 X 10(‐6) M, for ATP 8.3 X 10(‐6) M. Regional variations in the magnitude of the responses were observed. The largest responses were obtained from the muscular strip of sinus venosus near its junction with atrium, and from the right horn of the sinus venosus. In interauricular septum the adenyl compounds caused only a slight increase in isotope efflux. Acetylcholine, by contrast, produced large increases in 86Rb efflux from all these preparations. Thus the distribution of the purinoceptors in the tortoise heart is more confined than that of the muscarinic receptors. Antagonism of the response to adenyl compounds by theophylline and 8‐phenyltheophylline was studied. The apparent Ki for theophylline was 10(‐5) M; that for 8‐phenyltheophylline about 10(‐6) M. Atropine did not inhibit the responses to the adenyl compounds. These results indicate that the changes in K permeability produced by adenosine and ATP are mediated by P1‐purinoceptors. The adenosine transport inhibitors, dipyridamole and nitrobenzylthioinosine (NBMPR), had no effect on the adenyl‐induced responses, indicating that adenosine uptake is of little importance in tortoise sinus venosus. The effects of phosphate‐modified ATP analogues were studied. Adenylimidodiphosphate (APPNP) produced increases in 86Rb efflux similar to those found with ATP, confirming that breakdown of ATP to adenosine is not obligatory for its action at P1‐purinoceptors. Alpha‐beta methylene ATP (APCPP) and beta‐gamma methylene ATP (APPCP) produced much smaller effects, which may be explained by their structural and chemical differences from ATP. The use of 86Rb as a tracer (Rb: K less than 0.01 in load solution) gives qualitatively similar results to those obtained when 43K is used to study the permeability increases produced by the adenyl compounds or acetylcholine. Quantitative differences in the measures obtained with the two isotopes, however, become apparent when the efflux of both is studied simultaneously.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of deuterium oxide on calcium transients and myofibrillar responses of frog skeletal muscle.
Authors: Allen D G , Blinks J R , Godt R E
Published: December 2014

The influence of substituting D2O for H2O on calcium transients and on contraction was studied in intact single skeletal muscle fibres injected with aequorin and in mechanically skinned fibres from frogs. Most experiments were carried out at 10 degrees C. Experiments performed in vitro established that the calcium concentration‐effect curve for aequorin is depressed and the rate of change of aequorin light emission after sudden changes of [Ca2+] is decreased when D2O is substituted for H2O. D2O substitution greatly reduces the amplitude of the aequorin signals of intact fibres both in twitches and in tetani. This is partly the result of the influence of D2O on aequorin, but the amplitude of the calcium transients is reduced as well. In both H2O and D2O Ringer solutions, the amplitude and time course of the sarcoplasmic calcium transient during a tetanus vary greatly with the stimulus frequency. In H2O, frequencies high enough to produce mechanical fusion normally produce cytoplasmic calcium concentrations high enough to saturate the myofibrils, with the result that stimulus frequency has very little influence on the mechanical response. Saturation does not occur in D2O, and the amplitude and form of fully fused tetani are greatly influenced by the frequency of stimulation. Aequorin was used as a calcium indicator to estimate the influence of D2O substitution on the apparent equilibrium association constant for the calcium‐EGTA complex. The constant was reduced by more than one order of magnitude in D2O at pD = pH = 7.0. Experiments on mechanically skinned muscle fibres showed that D2O substitution decreased the apparent sensitivity of the myofibrils to calcium, but increased the force of contraction at saturating calcium concentrations. The latter effect is probably responsible for the potentiation of tetanic tension that is observed in certain D2O/H2O mixtures or in H2O solutions immediately after a switch from D2O. In intact muscle fibres the potentiation of twitch or tetanic tension after a switch from D2O to H2O declines with a half‐time of about 25 s; this probably reflects the time course of exchange of intracellular D2O for H2O. The effects of D2O on the intracellular calcium transient appeared and disappeared with a half‐time of less than 1 s; this time is of the same order of magnitude as that calculated for the exchange of H2O and D2O in the T‐tubules. We conclude that D2O affects calcium release at a site in the T‐tubule which is more accessible to the extracellular space than to the intracellular space.
Rate of change of alveolar carbon dioxide and the control of ventilation during exercise.
Authors: Allen C J , Jones N L
Published: December 2014

The relationship between rate of change of alveolar PCO2 (delta PA, CO2/delta te), CO2 output (VCO2) and ventilation (VE) has been determined following a rapid increase in exercise intensity, to test the hypothesis that VE is related to VCO2 by a feed‐forward control system responding to delta PA, CO2/delta te. There was a close relationship between delta PA, CO2/delta te and VCO2 (delta PA, CO2/delta te = 3.2 VCO2 + 0.85), but delta PA, CO2/delta te increased more rapidly than VCO2. Increases in mean inspiratory flow, an index of inspiratory drive, were more closely related to changes in delta PA, CO2/delta te than to changes in VCO2. Increases in VE during transient and steady‐state conditions may be described by the equation: VE = 6.76 delta PA, CO2/delta te ‐3.50, a relationship which is consistent with a feed‐forward control system.
Mechanism of effect of dibutyryl cyclic adenosine 3',5'‐monophosphate on canine renal renin release.
Authors: Bondar N , Cadnapaphornchai P , McDonald F D , Taher S
Published: December 2014

We evaluated the effect of intrarenal arterial infusion of dibutyryl cyclic AMP on renal renin release. Dibutyryl cyclic AMP (300 micrograms/kg X min) produced significant and reversible increases in renin secretion rate, renal blood flow and urinary Na+ excretion. In the non‐filtering kidneys, dibutyryl cyclic AMP increased renin secretion rate and renal blood flow. In indomethacin‐treated dogs, dibutyryl cyclic AMP also produced significant and reversible increases in renin secretion rate and renal blood flow but had no effect on Na+ excretion. During infusion of dibutyryl cyclic AMP, infusion of the Ca ionophore A23187 failed to inhibit renin release. These findings suggest that the effect of dibutyryl cyclic AMP on renin release is not mediated by prostaglandins or intracellular Ca and does not involve the macula densa. We conclude that dibutyryl cyclic AMP has a direct effect on the juxtaglomerular cells.
Intraluminal distension pressure on intestinal lymph flow, serosal transudation and fluid transport in the rat.
Authors: Lee J S
Published: December 2014

Effect of distension pressure (d.p.) on the rate of lymph flow, serosal transudation and fluid transport was studied on an in vivo upper jejunal preparation. In the non‐absorptive state with isotonic Na2SO4 solution as the luminal fluid, neither lymph flow nor transudation was increased with increasing d.p. from 0 to 3, 10, 20, 40 or 70 mmHg. Fluid absorption rate (Jv) increased by more than 100% when d.p. was increased from 0 to 3 mmHg whether glucose was present or absent in the luminal fluid (Krebs‐Ringer solution). In the presence of glucose, there was no difference in Jv in the range of d.p. between 3 and 70 mmHg. In the absence of glucose Jv decreased when d.p. was above 10 mmHg. Whether with or without glucose, lymph flow did not change between d.p. of 0 and 10 mmHg but decreased at higher pressures. Whether with or without glucose, transudation began to appear at d.p. of 10 mmHg, increased with increasing d.p. up to 70 mmHg, but was much less in the absence of glucose. Protein concentration in the lymph (1.5‐2.4% (w/v] and transudation (1.5‐2.1% (w/v] was practically the same, suggesting that the latter could have originated from the lymph which leaked out of the serosal membrane. Blood flow in the subserosal capillaries and venules was remarkably reduced when d.p. was above 10 mmHg. In both jejunum and ileum, d.p. never caused fluid secretion during distension but resulted in transient fluid secretion as well as transudation following distension, apparently due to increased capillary filtration as a result of increased capillary permeability by ischaemia (during distension). From the effect of d.p. on the increase of transudation, presumably lymph, it is concluded that luminal hydrostatic pressure may play a role in fluid transport via the lymphatic system.
Calcium‐dependent after‐potentials in visceral afferent neurones of the rabbit.
Authors: Higashi H , Morita K , North R A
Published: December 2014

Intracellular recordings were made from neurones in nodose ganglia excised from rabbits. In C neurones, 1‐60 action potentials were followed by an after‐hyperpolarization with a peak amplitude of 16 mV and a time constant of decay ranging from 3 to 10 s. In A neurones, the action potentials were followed only by a brief (up to 50 ms) after‐hyperpolarization. The after‐hyperpolarization was associated with an increase in the membrane conductance to potassium ions; it reversed polarity at the potassium equilibrium potential. The increase in conductance following the action potentials was blocked by removal of calcium ions, or addition of cobalt to the extracellular solution. Intracellular injection of ethyleneglycol‐bis(beta‐aminoethylether)‐N,N'‐tetraacetic acid (EGTA) abolished the after‐hyperpolarization; intracellular injection of calcium mimicked the after‐hyperpolarization. It is concluded that calcium entry during the action potential leads to a long‐lasting increase in potassium conductance in visceral afferent C neurones.
Effects of selective alpha 1‐, alpha 2‐, beta 1‐and beta 2‐adrenoceptor stimulation on potentials and contractions in the rabbit heart.
Authors: Dukes I D , Vaughan Williams E M
Published: December 2014

Selective adrenoceptor agonists and antagonists have been used to analyse the effects of stimulation of individual types of adrenoceptor in various parts of the rabbit heart. The selective alpha 1‐ and alpha 2‐adrenoceptor agonists used were St 587 and BHT 933 respectively, and the antagonists were prazosin (alpha 1) and WY 25309 (alpha 2). The selective beta 1‐ and beta 2‐adrenoceptor antagonists were atenolol and ICI 118551, respectively. Pirbuterol was a highly selective beta 2‐adrenoceptor agonist. The non‐selective agonists noradrenaline, adrenaline and isoprenaline were also employed with various combinations of antagonists. Phenylephrine was found to stimulate beta‐ as well as alpha‐adrenoceptors. Rimiterol was a beta‐adrenoceptor agonist, partially selective for beta 2‐adrenoceptors. In the sinus node beta 1‐, but not beta 2‐adrenoceptor stimulation increased the fast phase of depolarization (Vmax). Both beta 1‐ and beta 2‐adrenoceptor stimulation increased the slope of slow diastolic depolarization, accelerated repolarization and increased maximum diastolic potential. After blockade of both beta 1‐ and beta 2‐adrenoceptors alpha 1‐adrenoceptor stimulation caused bradycardia, due exclusively to delayed repolarization. alpha 2‐adrenoceptor stimulation had no effect. In Purkinje cells and papillary muscle both beta 1‐ and beta 2‐adrenoceptor stimulation accelerated repolarization. Stimulation of alpha 2‐adrenoceptors had no effect. Beta 1‐, not beta 2‐adrenoceptor stimulation augmented peak contractions 3‐5‐fold, and greatly increased rate of development of tension. After beta‐blockade alpha 1‐adrenoceptor stimulation moderately increased peak contractions (up to 47%), but increased time‐to‐peak and duration of contractions. These patterns of adrenoceptor‐mediated effects were unchanged in animals pre‐treated with sufficient 6‐hydroxydopamine to eliminate responses to sympathetic nerve stimulation. The results would be consistent with beta 1‐, and beta 2‐adrenoceptor stimulation increasing inward calcium current, and with stimulation of alpha 1‐adrenoceptors delaying its inactivation, rather than increasing its magnitude.
The reflex effects of changes in carotid sinus pressure upon renal function in dogs.
Authors: Karim F , Poucher S M , Summerill R A
Published: December 2014

In chloralose‐anaesthetized and artificially ventilated dogs, the carotid sinuses were vascularly isolated and perfused with arterial blood. Mean aortic pressure was held constant at 100 +/‐ 2 mmHg (mean +/‐ S.E. of mean, n = 19) by means of a pressure bottle connected to the aorta. Both vagus nerves were sectioned in the neck and propranolol hydrochloride (0.5 mg kg‐1) was administered every 30 min. The left renal blood flow was measured by an electromagnetic flowmeter (wrap‐round probe), glomerular filtration rate by creatinine clearance and urinary sodium by flame photometry. Decreasing pressure in the isolated carotid sinuses from 186 +/‐ 10 to 63 +/‐ 5 mmHg resulted in significant decreases in renal blood flow from 281 +/‐ 35 to 177 +/‐ 30 ml min‐1 100 g‐1 renal mass; glomerular filtration rate from 40.0 +/‐ 7.8 to 12.3 +/‐ 4.4 ml min‐1 100 g‐1; urine flow from 0.31 +/‐ 0.05 to 0.12 +/‐ 0.03 ml min‐1 100 g‐1 and sodium excretion from 21.7 +/‐ 7.2 to 8.2 +/‐ 3.0 mumol min‐1 100 g‐1. Increasing carotid sinus pressure back to 188 +/‐ 11 mmHg resulted in increases in all the variables to values not significantly different from their initial values. Tying renal sympathetic nerves at low carotid sinus pressure (73 +/‐ 11 mmHg) caused an increase in all of the variables. After denervation there was no response to changes in carotid sinus pressure. These results show that changes in carotid sinus pressure can result in significant reflex effects on renal function and that these effects are mediated by renal sympathetic nerves.
Inhibitory synaptic potentials resulting from alpha 2‐adrenoceptor activation in guinea‐pig submucous plexus neurones.
Authors: North R A , Surprenant A
Published: December 2014

Intracellular recordings were obtained from neurones of the guinea‐pig submucous plexus. Inhibitory synaptic potentials (i.p.s.p.s) were compared with hyperpolarizations evoked by brief, local applications of noradrenaline and by superfusion with adrenoceptor agonists. Hyperpolarizing potentials elicited by brief applications of noradrenaline were similar to the i.p.s.p. in latency of onset, amplitude, time course, conductance increase, reversal potential and ionic dependence. Both responses were blocked by low concentrations of Ba2+ and quinine. 6‐hydroxydopamine selectively and irreversibly abolished the i.p.s.p. and resulted in a complete loss of catecholamine fluorescent nerve fibres in the submucous plexus. The alpha 2‐adrenoceptor antagonists, phentolamine, yohimbine and RX781094, reversibly blocked the i.p.s.p. and the noradrenaline hyperpolarization. Prazosin, propranolol, atropine and naloxone had no effect on these responses. Superfusion with noradrenaline and clonidine produced dose‐dependent membrane hyperpolarizations. Noradrenaline and clonidine dose‐hyperpolarization curves were shifted to the right in a parallel fashion by alpha 2‐adrenoceptor antagonists. Determination of the dissociation equilibrium constants for phentolamine, yohimbine and RX781094 showed that the hyperpolarization produced by noradrenaline perfusion is due to alpha 2‐adrenoceptor activation. It is concluded that the release of noradrenaline from sympathetic nerves activates post‐synaptic alpha 2‐adrenoceptors, resulting in the K+ conductance increase which underlies the i.p.s.p. in submucous plexus neurones.
Effects of L‐glutamate on the anomalous rectifier potassium current in horizontal cells of Carassius auratus retina.
Authors: Kaneko A , Tachibana M
Published: December 2014

The effects of externally applied L‐glutamate (Glu) on K currents through the anomalous rectifier were studied in solitary horizontal cells dissociated from goldfish retinae under whole‐cell voltage‐clamp or cell‐attached patch‐clamp conditions using 'giga‐seal' suction pipettes. In the whole‐cell clamp experiments, hyperpolarization of the membrane below the resting potential (ca. ‐57 mV) induced a large voltage‐dependent inward current which has been identified as the K current through the anomalous rectifier (Ianomal.). Application of Glu to the external medium reduced Ianomal.. Reduction of the inward current was not seen in preparations in which Ianomal. has been blocked by an application of Cs or Ba ions to the external medium. Single‐channel currents through the anomalous rectifier were recorded under cell‐attached patch‐clamp conditions. The current showed an inward rectification; its amplitude increased with hyperpolarization of the patch membrane, and became below the noise level near the equilibrium potential of K ions (EK). No polarity reversal was observed even by a strong membrane depolarization. The patch membrane potential at which the current amplitude became undetectable shifted in parallel to the shift of EK. The open probability changed little with polarization of the patch membrane. When Glu (greater than 100 microM) was applied to the outside of the patch membrane, the number of available Ianomal. channels was decreased, but neither the single‐channel conductance, open or closed time constants, nor the open probability changed significantly. Removal of Glu produced the opposite sequence; i.e. the number of available Ianomal. channels increased with time. It was concluded that the reduction of the Glu‐induced current at hyperpolarized potentials in the whole‐cell recording configuration is due to the blocking action of Glu on Ianomal..
A voltage‐gated potassium channel in human T lymphocytes.
Authors: Cahalan M D , Chandy K G , DeCoursey T E , Gupta S
Published: December 2014

Human peripheral T lymphocytes were studied at 20‐24 degrees C using the gigaohm seal recording technique in whole‐cell or outside‐out patch conformations. The predominant ion channel present under the conditions employed was a voltage‐gated K+ channel closely resembling delayed rectifier K+ channels of nerve and muscle. The maximum K+ conductance in ninety T lymphocytes ranged from 0.7 to 8.9 nS, with a mean of 4.2 nS. The estimated number of K+ channels per cell is 400, corresponding to a density of about three channels/micron2 apparent membrane area. The activation of K+ currents could be fitted by Hodgkin‐Huxley type n4 kinetics. The K+ conductance in Ringer solution was half‐maximal at ‐40 mV. The time constant of K+ current inactivation was practically independent of voltage except near the threshold for activating the K+ conductance. Recovery from inactivation was slow and followed complex kinetics. Steady‐state inactivation was half‐maximal at ‐70 mV, and was complete at positive potentials. Permeability ratios, relative to K+, determined from reversal potential measurements were: K+(1.0) greater than Rb+(0.77) greater than NH4+(0.10) greater than Cs+ (0.02) greater than Na+(less than 0.01). Currents through K+ channels display deviations from the independence principle. The limiting outward current increases when external K+ is increased, and Rb+ carries less inward current than expected from its relative permeability. Tail current kinetics were slowed about 2‐fold by raising the external K+ concentration from 4.5 to 160 mM, and were 5 times slower in Rb+ Ringer solution than in K+ Ringer solution. Single K+ channel currents had two amplitudes corresponding to about 9 and 16 pS in Ringer solution. Replacing Ringer solution with isotonic K+ Ringer solution increased the unitary conductance and resulted in inward rectification of the unitary current‐voltage relation. Comparable effects of external K+ were seen in the whole‐cell conductance and instantaneous current‐voltage relation. Several changes in the K+ conductance occurred during the first few minutes after achievement of the whole‐cell conformation. Most are explainable by dissipation of a 10‐20 mV junction potential between pipette solution and the cytoplasm, and by the use of a holding potential more negative than the resting potential. However, inactivation of K+ currents became faster and more complete, changes not accounted for by these mechanisms. K+ efflux through open K+ channels in intact lymphocytes, calculated from measured properties of K+ channels, can account for efflux values reported in resting lymphocytes, and for the increase in K+ efflux upon mitogenic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Cholinergic mechanisms in human coronary artery preparations: implications of species differences.
Authors: Kalsner S
Published: December 2014

Acetylcholine dilates most arteries, including dog coronaries, if the endothelium is intact. The present study has shown only contraction of human coronary arteries to acetylcholine. Both strip and ring preparations of human coronary epicardial vessels, the latter done particularly to protect the intimal surface from unintentional denudation, contracted to acetylcholine at low to high concentrations (6.84 X 10(‐9)‐2.05 X 10(‐5) M). These responses were blocked by atropine (3.45 X 10(‐6) M). Acetylcholine contracted the arteries about as much as ergonovine and considerably more than noradrenaline. Field stimulation of coronary artery strips caused a vasoconstriction which was partially antagonized by atropine (3.45 X 10(‐6) M). The release of [3H]noradrenaline from superfused coronary artery preparations during field stimulation was inhibited by methacholine (6.24 X 10(‐6) M), a stable muscarinic analogue of acetylcholine. Dog coronary arteries relaxed to acetylcholine but not if the endothelium was intentionally denuded, in which case there was either no response at all or a weak relaxation. Coronary arteries of sheep, pig and cattle always contracted to acetylcholine, and those of monkey contracted in two out of three responsive preparations. Histological examination of the intimal surface of human coronary vascular segments confirmed the presence of an intact endothelial cell layer. Rabbit aorta gave dilator responses to acetylcholine even after being left in the animal for as long after death as the human arteries had been; they did not give dilator responses after the endothelium was rubbed off. It is concluded that cholinergic vasoconstriction of coronary arteries occurs in humans, though not in the dog, and is probably important in some cases of coronary artery spasm.
Profiles of evoked release along the length of frog motor nerve terminals.
Authors: D'Alonzo A J , Grinnell A D
Published: December 2014

In order to determine the relative probability of evoked transmitter release from different parts of frog motor nerve terminals, a technique has been developed in which single quantum end‐plate potentials (e.p.p.s) are recorded by two intracellular electrodes, located at opposite ends of identified junctions. The log of the ratio of the amplitudes recorded simultaneously at the two electrodes is a linear function of the distance of the site of origin of the event from each of the two electrodes. Using online computer data acquisition and analysis, and current pulses at known locations for spatial calibration, it is possible to localize the site of single quantum e.p.p.s to within +/‐ 10‐20 micron. Using the frog cutaneous pectoris neuromuscular preparation and a low calcium, high magnesium Ringer solution to ensure mostly single quantum events and failures, several thousand responses were recorded from each junction, allowing construction of a profile of the numbers of single quantum events arising from each portion of the junction. By comparison of junctional morphology and release profiles, it is possible to construct a probability of release per unit length profile for the entire junction. This technique has several advantages over localization of release events by measurements of extracellular synaptic currents. It was found that, for most junctions, the central 60‐90% of the terminal exhibited relatively uniform probability of release, with highest levels typically near the point where the axon first contacted the muscle fibre, or in regions with many short terminal branches. However, no instances have been found in which a small region of terminal (10% or less) showed extraordinarily high release levels (30‐50% of the total release from the junction). Characteristically, but not invariably, there is reduced release near the ends of terminal branches, especially the longer branches, where release per unit length could be as little as 5‐10% of that in proximal portions. Some junctions had large regions of terminal that released very little transmitter. These also showed multiple myelineated axonal inputs, and may have been polyneuronally innervated junctions in which one of the inputs was much weaker than the other.
The admittance of the squid giant axon at radio frequencies and its relation to membrane structure.
Authors: Haydon D A , Urban B W
Published: December 2014

The admittance of the squid giant axon membrane has been measured, using an intracellular electrode, at frequencies up to 40 MHz. The existence of a radio frequency dispersion, previously detected with extracellular electrodes (Cole, 1976) and attributed to the Schwann cell layer, has been confirmed and followed to higher frequencies. For a comparable method of analysis, membrane parameters similar to those given by Cole (1976) have been calculated. The radio frequency dispersion has a centre frequency at approximately 1.8 MHz, and the properties of a parallel combination of a 28 nF cm‐2 capacity and a 3.3 omega cm2 resistance. When the axon membrane capacity is calculated, taking into account the radio frequency dispersion, as described above, the capacity remains frequency dependent throughout the range studied. If it is assumed that at high frequencies the axolemma capacity becomes constant at approximately the value for a lipid bilayer, a radio frequency dispersion is found which cannot be accounted for in terms of a simple equivalent circuit with two passive components, but appears to arise from a network with a distribution of relaxation times. This result could be consistent with the morphology of the Schwann cell layer. The radio frequency dispersion referred to in (4) can be described reasonably well by a circuit with two dispersions having centre frequencies of 250 kHz and 3.2 MHz respectively. The corresponding axolemma capacity (100‐500 kHz) would be approximately 0.6 microF cm‐2. It is argued that between 50 and 100 kHz the geometrical capacity arising from the non‐polar regions of the membrane is a major contributor to the axon membrane capacity, and that capacity variations arising from compositional changes in the lipid bilayer are best monitored in this frequency range.
Blockade of slow excitatory post‐synaptic potential by substance P antagonists in guinea‐pig sympathetic ganglia.
Authors: Konishi S , Otsuka M
Published: December 2014

The effects of three substance P (SP) antagonists on the inferior mesenteric ganglion of the guinea‐pig were studied using intracellular recording techniques, and the possible role of SP as a transmitter for the non‐cholinergic slow excitatory post‐synaptic potential (e.p.s.p.) was examined. The SP antagonist, [D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11]SP, exerted a depolarizing action on the ganglion cells when applied by perfusion at a concentration of 3‐16 microM or by pressure ejection from a micropipette. This depolarizing action is probably due to a release of endogenous histamine because it was abolished by treatment with a histamine antagonist, mepyramine (1‐3 microM), or by a repeated application of the antagonist. When applied by pressure ejection, SP at 0.5‐1 microM depolarized the ganglion cells. In the presence of mepyramine, [D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11]SP suppressed the SP‐induced depolarization by 41% at a concentration of 8 microM and by 75% at 16 microM. By contrast the SP antagonist did not affect the depolarizing action of angiotensin II on the ganglion cells. The non‐cholinergic slow e.p.s.p. evoked in the ganglion cells by repetitive stimulation of the lumbar splanchnic nerves was suppressed by [D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11]SP at 8 or 16 microM. The degrees of suppression of both the non‐cholinergic slow e.p.s.p. and the SP‐induced depolarization by the SP antagonist were approximately equal. The cholinergic fast e.p.s.p. evoked by preganglionic nerve stimulation was not affected by the SP antagonist. [D‐Pro2, D‐Trp7,9]SP exhibited the properties of an SP antagonist similar to, but slightly weaker than [D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11]SP. [D‐Pro2, D‐Phe7, D‐Trp9] at a concentration of 16 microM had a depolarizing action on the ganglion cells, which was not blocked by mepyramine. The peptide exerted hardly any antagonistic action against the SP‐induced depolarization of the ganglion cells. Stimulation of the other preganglionic (intermesenteric) nerves and the post‐ganglionic (colonic and hypogastric) nerves produced a non‐cholinergic slow e.p.s.p. in the inferior mesenteric ganglion cells. The non‐cholinergic slow e.p.s.p. evoked by both pre‐ and post‐ganglionic nerve stimulation were depressed by [D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11]SP to similar extents. The present results show that [D‐Arg1, D‐Pro2, D‐Trp7,9, Leu11]SP and [D‐Pro2, D‐Trp7,9]SP can serve as specific SP antagonists in the inferior mesenteric ganglion of the guinea‐pig.(ABSTRACT TRUNCATED AT 400 WORDS)