bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual effects of dihydropyridines on whole cell and unitary calcium currents in single ventricular cells of guinea‐pig.
Authors: Brown A M , Kunze D L , Yatani A
Published: December 2014

We studied the effects of dihydropyridine Ca channel ligands (DHPs), mainly nitrendipine and Bay K8644, on whole cell and single channel Ca currents on single myocytes isolated from the adult guinea‐pig ventricle. Nitrendipine had dual effects, stimulatory or inhibitory, depending upon the membrane potential. At low frequencies (less than 0.03 Hz) and negative holding potentials (‐90 mV or more), nitrendipine increased the Ca currents in a dose‐dependent manner. The dose‐response curve was best fitted by a Langmuir adsorption isotherm model which was the sum of two independent one‐to‐one drug‐receptor sites with median effective doses (ED50S) of 1.0 X 10(‐9) M and 1.4 X 10(‐6) M respectively. When the membrane potential was held at ‐30 mV or less, nitrendipine inhibited the Ca currents, also in a dose‐dependent manner. The dose‐response curve was fitted by a single binding site model having a median inhibitor concentration (IC50) of 1.5 X 10(‐9) M. At holding potentials between ‐70 and ‐40 mV, nitrendipine produced mixed effects on Ca currents; an increase occurred initially and this was followed by a decrease. When rundown was excluded, Bay K8644 showed only stimulatory effects on the Ca currents between holding potentials of ‐120 and ‐30 mV. When the test potential was zero or +10 mV the Ca currents reached peak values and the dose‐response curve was best fitted by a single binding site model having an ED50 of 3 X 10(‐8) M. When the effects were measured at negative test potentials of ‐30 to ‐10 mV, the curve was best fitted by a two‐site model with ED50S of 3 X 10(‐9) and 9 X 10(‐7) M. At the single Ca channel level the stimulatory effect of nitrendipine was due to an increased probability that a Ca channel which had opened once would reopen, a reduction in records without activity and an increase in the mean open time. There were no changes in unit conductance. Inhibitory effects were due to a large increase in nulls. At lower concentrations the main effect of Bay K8644 was an increase in the probability of opening. At doses above 10(‐6) M, a pronounced increase in the open time was observed. The effects we observed are attributed to at least two sites for DHP related to Ca channels; one with high affinity and one with a lower affinity. The low affinity site mediates a stimulatory effect due to greatly prolonged openings.(ABSTRACT TRUNCATED AT 400 WORDS)
Potential‐dependent calcium inward current in a single isolated smooth muscle cell of the guinea‐pig taenia caeci.
Authors: Ganitkevich VYa  , Shuba M F , Smirnov S V
Published: December 2014

A single glass micropipette voltage‐clamp technique was used to study a potential‐dependent calcium inward current in isolated smooth muscle cells of the guinea‐pig taenia caeci. Experiments were performed at 22‐24 degrees C. With potassium as the main cation in the pipette solution, a transient inward current appeared in response to a depolarizing pulse, followed by an outward current. The replacement of potassium ions by caesium ions and TEA (tetraethyl‐ammonium) in the pipette solution resulted in an effective suppression of potassium outward current permitting a study of the calcium current solely. The calcium inward current was blocked by 5 mM‐cobalt and 5 X 10(‐6) M‐verapamil. Activation of the calcium current occurred at a membrane potential of between ‐35 and ‐25 mV. The calcium current was maximal in the potential range +10 to +20 mV and did not reverse even at +60 mV. Inactivation of the calcium current had a complex nature. It did not inactivate completely even during depolarizations lasting many seconds. During the first 400 ms the decay of the calcium current followed a time course described by two exponentials. The fast time constant of decay was in the range of 40 to 53 ms (n = 3) and the slow time constant was approximately 10‐fold greater (at 0 mV). The fast time constant did not depend on the membrane potential while the slow time constant decreased with depolarization. Availability of the calcium current was estimated in double‐pulse experiments. It had a U‐shaped dependence on the conditioning potential; maximal inactivation was observed at potentials corresponding to the maximal calcium current. It was suggested that a component of inactivation was dependent on the calcium current which flowed. Calculations of calcium entry at various depolarizations showed that large amounts of calcium ions enter the cell. Also, it was suggested that calcium ions are effectively bound within the smooth muscle cell.
The differential effects of twitch potentiators on charge movements in frog skeletal muscle.
Authors: Huang C L
Published: December 2014

The effects of twitch potentiators at physiologically effective concentrations on intramembrane charge movements were examined in voltage‐clamped frog skeletal muscle in the presence and absence of tetracaine. Caffeine, even at high concentrations (2.5 mM) did not alter the potential dependence of either tetracaine‐sensitive or tetracaine‐resistant portions of non‐linear charge through a voltage range that included the mechanical threshold. Perchlorate (8 mM) altered the form and shifted the potential dependence of the non‐linear charge by about ‐25 mV in the hyperpolarizing direction, but did not alter the total available charge. Comparing charge movements in the presence and absence of 4 mM‐tetracaine demonstrated that perchlorate shifted the threshold and voltage dependence of the delayed ('q gamma') transients but had no action on the steady‐state tetracaine‐resistant charge. Thiocyanate (10 mM) shifted the voltage dependence of charge movements by about 20 mV in the hyperpolarizing direction. Experiments employing 4 mM‐tetracaine demonstrated that this was the result of effects on both tetracaine‐sensitive and tetracaine‐resistant charge movements. On the basis of their effects on contractile activation reported on earlier occasions, these differential effects of twitch potentiators are explicable in terms of tetracaine‐sensitive and tetracaine‐resistant charge components being causally separate and not requiring a direct participation of tetracaine‐resistant charge in contractile activation.
Involvement of N‐methyl‐D‐aspartate receptors in epileptiform bursting in the rat hippocampal slice.
Authors: Dingledine R , Hynes M A , King G L
Published: December 2014

The effects of the N‐methyl‐D‐aspartate (NMDA) receptor antagonist, D‐2‐amino‐5‐phosphonovaleric acid (D‐APV), and other excitatory amino acid antagonists, were studied on CA1 pyramidal neurones treated with picrotoxin or bicuculline to reduce synaptic inhibition mediated by gamma‐aminobutyric acid (GABA). Under these conditions epileptiform burst firing is readily produced by orthodromic stimulation of the pyramidal cell population. D‐APV reduced the plateau amplitude and duration of the depolarization underlying evoked and spontaneous bursts without affecting membrane potential, input resistance or the ability of the cell to fire a Ca2+ spike or a short train of Na+ spikes. A late component of the subthreshold excitatory post‐synaptic potential (e.p.s.p.) was voltage dependent, being reduced in amplitude on membrane hyperpolarization. D‐APV selectively removed this component of the e.p.s.p. in disinhibited slices. In contrast, in the absence of GABA antagonists, D‐APV had no noticeable effect on the e.p.s.p. as studied with field potential recordings. The concentration‐response relationship of the inhibitory effect of D‐APV and L‐APV on population spike bursts was studied. The action of APV was highly stereoselective; the EC50 of D‐APV was approximately 700 nM, whereas a similar inhibition required 540 microM‐L‐APV. A number of other excitatory amino acid antagonists were tested at a fixed concentration (100 microM). Among them, the quisqualate antagonist gamma‐D‐glutamylaminomethyl sulphonic acid was ineffective against epileptiform bursts. In the low nanomolar concentration range both D‐ and L‐APV potentiated bursting. These results suggest that in the absence of GABAergic inhibition, a significant component of the slow depolarization underlying burst firing is voltage dependent, synaptic in origin and mediated by NMDA receptors. We propose that, under normal (non‐epileptic) physiological conditions, the balance between synaptic inhibition mediated by GABA receptors and synaptic excitation mediated by NMDA receptors may modulate the excitability of pyramidal cell dendrites.
The effect of adrenergic, cholinergic and peptidergic salivary stimulants on gastric mucosal integrity in the rat.
Authors: Soper B D , Tepperman B L
Published: December 2014

Sialoadenectomized and sham‐operated rats were given salivary secretory stimulants 30 min prior to intragastric instillation of a bile salt solution (5 mM‐sodium taurocholate in 100 mM‐HCl). Administration of the alpha‐agonist phenylephrine (0.15‐15 mg/kg) resulted in a dose‐dependent reduction in the loss of H+ and the intraluminal appearance of Na+ and K+ associated with bile‐salt‐induced damage to the stomach in the sham‐sialoadenectomized rat. The effect was not apparent if the salivary glands had been previously excised. Adrenaline (0.8‐4.0 mg/kg) and noradrenaline (0.8‐4.0 mg/kg) were less effective in reducing the degree of mucosal damage in sham‐sialoadenectomized rats and were not effective in sialoadenectomized rats. Administration of secretory stimulant doses of isoprenaline (5 mg/kg), pilocarpine (2 mg/kg) and substance P (25 mg/kg) either had no significant effect or exacerbated the net transmucosal fluxes of H+, Na+ and K+ associated with bile salt damage to the gastric mucosa. The protective action of phenylephrine in sham‐sialoadenectomized rats was reversed by prior treatment with the alpha‐antagonist, phentolamine (2 mg/kg). The effect of phentolamine was dose dependent. Vagotomy abolished the protective influence of phenylephrine in sham‐sialoadenectomized rats but did not influence the response to other salivary secretory stimulants consistently. These data suggest that stimulation of alpha‐adrenergic receptors in rat salivary tissue is associated with an amelioration of the increase in gastric mucosal permeability to H+, Na+ and K+ in response to an intraluminal bile salt solution. The apparent protective influence of alpha‐adrenergic receptor activation in sham‐sialoadenectomized rats is mediated in part by the vagus nerve.
The effects of electrical stimulation of myelinated and non‐myelinated vagal fibres on heart rate in the rabbit.
Authors: Ford T W , McWilliam P N
Published: December 2014

The bradycardia evoked by electrical stimulation of the peripheral end of the rabbit vagus nerve is mediated by both myelinated and non‐myelinated fibres. Stimulation of myelinated fibres at 5 Hz for 20 s resulted in a fall in heart rate from a control value of 204 +/‐ 1.3 to 182 +/‐ 1.2 beats min‐1 (means + S.E. of means). On stimulation of both myelinated and non‐myelinated fibres, heart rate fell to 169 +/‐ 2.1 beats min‐1. Heart rate returned rapidly to control value following stimulation of myelinated fibres but only slowly after stimulation of both myelinated and non‐myelinated fibres. Thus recruitment of non‐myelinated fibres increased both the magnitude and duration of the bradycardia. Atropine abolished all effects of vagal stimulation on heart rate. Hexamethonium abolished the effect of myelinated fibres on heart rate; however, recruitment of non‐myelinated fibres still produced a bradycardia. It is suggested that the prolonged effect following stimulation of non‐myelinated fibres may reflect the persistent action of a non‐cholinergic excitatory transmitter at the ganglion.
Serotoninergic and non‐serotoninergic responses of phrenic motoneurones to raphe stimulation in the cat.
Authors: Lalley P M
Published: December 2014

Experiments were conducted on anaesthetized, paralysed and artificially ventilated cats in order to determine if the altered discharge pattern of phrenic motoneurones recorded during stimulation of medullary raphe nuclei (raphe magnus (r. magnus), raphe obscurus (r. obscurus), raphe pallidus (r. pallidus] are related to release of serotonin (5‐hydroxytryptamine, 5‐HT) at synapses on respiratory neurones. Effects of 5‐HT released by the neurotoxin p‐chloroamphetamine (PCA) on spontaneous activity of phrenic motoneurones were also examined. In addition, responses of phrenic motoneurones to 5‐HT applied by micro‐electrophoresis were recorded. Stimulation (100 Hz) of r. magnus or r. obscurus depressed the spontaneous inspiratory discharges of phrenic motoneurones. Administration of the 5‐HT receptor antagonists cinanserin, methysergide or methergoline reduced, but did not abolish, the inhibition. Inhibition of the neuronal reuptake of 5‐HT with fluoxetine enhanced the inhibition and reduced the peak inspiratory action potential frequency of spontaneous discharges. Stimulation (100 Hz) of r. pallidus produced increased firing of phrenic motoneurones. Firing of phrenic motoneurones was evoked even during the normally quiescent expiratory phase of spontaneous respiratory activity. Antagonists at 5‐HT receptors reduced the degree of tonic firing, resulting in partial restoration of expiratory pauses during r. pallidus stimulation. Inhibition of 5‐HT reuptake, on the other hand, resulted in increased tonic firing. Release of 5‐HT by PCA produced a rapid and severe reduction of phrenic nerve activity. Activity was restored by 5‐HT receptor antagonists. In reserpine‐treated cats, effects of stimulating medullary raphe nuclei were still pronounced, however 5‐HT receptor antagonists had no effect on the responses. These results, along with the observation that 5‐HT receptor antagonists are only partially effective in non‐reserpinized cats, indicate that non‐serotoninergic influences contribute as well to the responses evoked by raphe stimulation. Micro‐electrophoretic application of 5‐HT by large ejecting currents (100‐200 nA) had weak stimulatory effects on twenty of forty‐five phrenic motoneurones, which exhibited small increases in peak inspiratory discharge frequency during 5‐HT application. Ejecting currents less than 100 nA were without effect. It is concluded that 5‐HT analogues and agents which release endogenous 5‐HT after parenteral administration do not act directly at synapses on the soma membranes of phrenic motoneurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Kidney function in rats with corticomedullary nephrocalcinosis: effects of alterations in dietary calcium and magnesium.
Authors: Al-Modhefer A K , Atherton J C , Garland H O , Singh H J , Walker J
Published: December 2014

Single‐nephron and whole‐kidney function were studied in female rats with corticomedullary nephrocalcinosis, and in animals where the lesion had been prevented either by a dietary magnesium supplement or by using a diet with a calcium:phosphorus ratio in excess of 1. At the single‐nephron level, rats with nephrocalcinosis had prolonged tubular fluid transit times. Proximal transit time was 19.42 +/‐ 1.98 (mean +/‐ S.E. of mean) vs. 11.58 +/‐ 0.19 s for controls; distal transit time was 62.64 +/‐ 9.16 vs. 31.50 +/‐ 1.03 s for controls. Although single‐nephron function is altered in nephrocalcinosis, data obtained from rats in metabolism cages indicate that whole‐kidney function is largely unaffected by the lesion.
Redox state changes in human skeletal muscle after isometric contraction.
Authors: Henriksson J , Katz A , Sahlin K
Published: December 2014

Subjects maintained an isometric contraction of the quadriceps femoris muscle at two‐thirds maximal voluntary contraction (m.v.c.) force for 5 s (5.0 +/‐ 0.3 s; mean +/‐ S.E. of mean; n = 6) or until fatigue (52 +/‐ 4 s; n = 13). Muscle biopsies were obtained at rest, immediately after the contractions and also at 1 and 4 min of recovery after contraction to fatigue. In all subjects 5 s isometric contraction resulted in an increase of muscle NADH (0.084 +/‐ 0.012 at rest to 0.203 +/‐ 0.041 mmol/kg dry wt.) and a decrease of phosphocreatine (PC; change in concentration = ‐17.3 +/‐ 3.8 mmol/kg dry wt.). Glucose‐6‐phosphate concentration was more than doubled whereas lactate increased in only four of the six subjects. The two subjects who did not show any increase in lactate also had the lowest increase in NADH. At fatigue NADH increased to 0.226 +/‐ 0.032 mmol/kg dry wt. which was not significantly different from the value after 5 s contraction. Muscle PC was nearly depleted and lactate increased 12‐fold above resting levels. The major part (65%) of the NADH increase at fatigue had reverted after 1 min recovery but only a slight further decrease occurred between 1 and 4 min of recovery. In relative terms the time course of the changes in muscle NADH during the first minute of recovery was similar to that of PC resynthesis, suggesting a common regulator such as O2 availability. In contrast to the delayed return of NADH concentration, PC resynthesis continued during the later part of the recovery period and PC concentration was almost fully restored after 4 min of recovery. It is concluded that muscle NADH is already maximally increased in the first seconds of muscle contraction at two‐thirds m.v.c. Indirect evidence indicates that this increase reflects a reduction of the mitochondrial NAD‐NADH redox couple. The rapid establishment of a reduced mitochondrial redox state at the start of muscle contraction will probably lead to a reduction of the redox state in the cytoplasm also and therefore be important for enhancing lactate formation.
Effects of visual deprivation on the development of the monkey's lateral geniculate nucleus.
Authors: Blakemore C , Vital-Durand F
Published: December 2014

We have studied the physiological properties of cells in the deprived layers of the lateral geniculate nucleus (l.g.n.) in monkeys monocularly deprived from birth for up to 27 weeks, and compared them with results from the non‐deprived layers in the same animals and in a series of normal animals. Despite the relative shrinkage of cell bodies in the deprived layers, units were easily isolated, were visually responsive and could readily be classified as linear (X) or non‐linear (Y) by means of tests of spatial summation. The laminar distribution of cell types and the proportion of Y cells did not seem to be affected by deprivation. The patterns and latencies of discharge produced by contrast‐reversing gratings did not differ grossly between deprived and non‐deprived cells. The peak firing frequencies for drifting gratings were also similar. The degree of surround antagonism (though very variable from cell to cell) seemed unaffected by deprivation. Most surprising of all, there was little or no deficit in the spatial resolution of the receptive fields of deprived cells. Recordings were always taken ipsilateral to the deprived eye, and neural 'acuity' tended to be sligtly lower in the deprived laminae than the non‐deprived. However, this nasal/temporal asymmetry in spatial resolution was not obviously more pronounced than in normal animals. Neural 'acuity' was not abnormally low in either contralateral or ipsilateral layers in the l.g.n. of an animal binocularly deprived from birth until a year of age. We have not examined chromatic properties or temporal characteristics adequately to say whether they are affected by deprivation. Paradoxically, although the post‐natal maturation of visual acuity in normal monkeys seems to be mainly limited by peripheral factors, deprivation (which causes a profound defect of behavioural acuity) does not seem to interfere substantially with physiological development of the retina or the geniculate nucleus.
Suppression of non‐shivering thermogenesis in the rat by heat‐seeking behaviour during cold exposure.
Authors: Morimoto A , Murakami N , Nakamori T , Watanabe T
Published: December 2014

Changes in rectal temperature (Tre) during cold exposure (0 +/‐ 1 degrees C) were observed in three groups of rats: heat‐seeking, no‐behaviour and semi‐restrained groups. Significant increases in Tre were observed in the no‐behaviour and the semi‐restrained groups during cold exposure. In the heat‐seeking behaviour group Tre remained constant during cold exposure. The increased Tre in the semi‐restrained group during cold exposure was markedly attenuated by the systemic injection of beta‐blocker (propranolol: 10 mg/kg, I.P.), indicating that this increase of Tre was caused by activation of non‐shivering thermogenesis (n.s.t.). Furthermore, the rise in Tre in the semi‐restrained group was preceded by a greater increase in the temperature of the interscapular brown adipose tissue. Using the autoradiographic [14C]deoxyglucose technique, it was revealed that the enhanced n.s.t. in the no‐behaviour and the semi‐restrained groups was accompanied by a significant increase of metabolic activity in the anterior part of the ventromedial hypothalamus. We conclude that during cold exposure motionlessness of slightly restrained animals increase n.s.t. when thermoregulatory behaviour to gain heat is not available. This increased n.s.t. is mediated by activation of hypothalamic function.
The effect of potassium on carotid body chemoreceptor discharge in the anaesthetized cat.
Authors: Band D M , Linton R A
Published: December 2014

1. In exercise the arterial plasma potassium rises; we have investigated the possibility that such rises might affect the carotid body chemoreceptor. 2. Intravenous infusions of KCl were used to produce hyperkalaemia in anaesthetized cats. 3. Intra‐arterial catheter tip potassium electrodes were used to monitor changes in plasma potassium. 4. The effects of 5 min infusions of KCl on afferent carotid chemoreceptor preparations were studied. 5. Infusions of KCl, which produced increases in plasma potassium similar to those occurring in exercise in man, caused an initial large increase in mean firing frequency (237% of control). A phase of rapid adaptation of this response was followed by a phase of slower adaptation, but after 5 min of hyperkalaemia mean firing frequency was still significantly greater than control. The amplitude of the breath‐by‐breath oscillation in frequency appeared to increase in parallel with mean frequency so that the amplitude/mean ratio remained constant. 6. We conclude that plasma potassium changes during exercise may contribute to the chemical drive to breathe.
Glycolysis and oxidative phosphorylation during activation of the sodium pump in the taenia from guinea‐pig caecum.
Authors: Takai A , Tomita T
Published: December 2014

1. In the taenia from the guinea‐pig caecum, the relative contribution of glycolysis and oxidative phosphorylation to activation of the Na pump was estimated by measuring changes in the rate of O2 consumption (QO2) and lactate production (Q1act). The Na pump was activated by K readmission following prior treatment with K‐free solution. The QO2 and Q1act were both increased significantly by K readmission 60 min after exposure to K‐free solution. These changes and the reaccumulation of tissue K were abolished by ouabain (10 microM). Spontaneous mechanical activity ceased in K‐free solution and the K‐induced increase in QO2 and Q1act was produced before the mechanical activity was restarted. 2. Similar changes were obtained when ouabain (10 microM) was removed after 60 min treatment. It was estimated from the changes in QO2 and Q1act that the oxidative and glycolytic metabolism each supplied about 50% of the total ATP demand for pump activation. 3. In Ca‐free solution, the increase in QO2 caused by K readmission was transient and QO2 returned to the previous value in K‐free solution in 10‐20 min. However, the increase in QO2 was maintained in the absence of glucose. When glucose was replaced with beta‐hydroxybutyrate (beta‐HB, 11.8 mM), which is metabolized only through oxidative phosphorylation, K readmission also produced a sustained increase in QO2. 4. In glycogen‐depleted preparations, K readmission produced little or no increase in QO2 in the absence of substrate or in the presence of glucose. On the other hand, in the presence of beta‐HB (11.8 mM), a typical increase in QO2 (about 0.1 mumol min‐1 g‐1) was observed in response to K readmission. Lactate production was negligible in the absence of substrate or in the presence of beta‐HB, but it was significantly increased after K readmission in the presence of glucose. The increase in tissue K content following K readmission was the same in the presence of glucose or beta‐HB. 5. In the glycogen‐depleted preparations the increase in QO2 caused by beta‐HB was dependent on the presence of both Na and K in the medium, and sensitive to ouabain. Furthermore, this response was reversibly suppressed by glucose.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of the intracellular pH‐regulating systems of frog skeletal muscle.
Authors: Putnam R W , Roos A , Wilding T J
Published: December 2014

1. The properties of the systems that regulate intracellular pH (pHi) in frog muscle (Rana pipiens) were studied in semitendinosus fibres using pH‐sensitive micro‐electrodes. All experiments were done at 22 degrees C and at external pH (pHo) 7.35. 2. Normally polarized fibres acidified to pHi approximately 6.8 by an NH4Cl pre‐pulse (nominal absence of CO2) recovered at a rate of 0.26 +/‐ 0.04 delta pHi h‐1 (n = 10). This corresponds to a net equivalent H ion efflux, JH, of 5.0 pmol cm‐2 s‐1. This rate was not affected by depolarizing the fibres to ‐20 mV in 50 mM‐K, constant Cl (0.29 +/‐ 0.03 delta pHi h‐1, JH = 4.9 pmol cm‐2 s‐1, n = 13). Amiloride (1 mM) reduced recovery by almost 90%, while 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS, 0.1 mM) reduced recovery by only 18%. Removal of external Na (substitution by N‐methyl‐D‐glucammonium) abolished recovery. Thus, Na‐H exchange is responsible for most of the recovery from acidification induced by an NH4Cl pre‐pulse. 3. The rate of recovery after an NH4Cl pulse increased linearly as pHi was reduced from 7.25 to 6.55. The dependence of this recovery upon external Na (at pHi 6.90) can be described by Michaelis‐Menten kinetics; the apparent Michaelis constant (Km) is 12 +/‐ 3 mM. 4. Recovery of normally polarized fibres from acidification induced by 5% CO2 is very slow (about 0.03 delta pHi h‐1). This recovery could be converted into an acidification of 0.06‐0.07 delta pHi h‐1 either by removal of Na (as previously described) or by amiloride. We ascribe this acidification of the polarized fibres to HCO3‐ efflux. 5. In fibres depolarized in 50 mM‐K, at constant external Cl concentration, recovery from CO2 acidification was brisk (0.28 +/‐ 0.01 delta pHi h‐1, JH = 9.4 pmol cm‐2 s‐1, n = 66). It was reduced by about 50% with either SITS or amiloride, and abolished by removal of Na. In the absence of Cl (substituted by gluconate), recovery was also reduced by about 50% and was unaffected by SITS, but nearly abolished by amiloride. Thus, in depolarized fibres, in addition to Na‐H exchange, there is an active, SITS‐sensitive component of recovery that requires Na, Cl and HCO3.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of calcium and other divalent cations on intracellular pH regulation of frog skeletal muscle.
Authors: Putnam R W , Roos A
Published: December 2014

1. We examined, in frog semitendinosus muscle, the effect of calcium release, induced by depolarization or caffeine, on intracellular pH (pHi) recovery from an acid load applied at least 40 min later. We also studied the effect of external Ca and other divalent cations on recovery. We used pH‐sensitive micro‐electrodes; the external pH (pHo) was always 7.35. 2. In fibres depolarized by 50 mM‐K, constant [K] X [Cl] in the presence of 1 mM‐tetracaine (which blocks Ca release), the rate of pHi recovery from 5% CO2‐induced acidification was 0.15 +/‐ 0.02 delta pHi h‐1 (n = 7), whereas in depolarized fibres that had never been exposed to the drug, the rate of recovery was 0.27 +/‐ 0.01 delta pHi h‐1 (n = 5). Yet, when Ca release was not blocked and the depolarized fibres were exposed to tetracaine shortly before CO2 exposure, a similar slow rate of 0.14 +/‐ 0.03 delta pHi h‐1 (n = 7) was observed. When Ca release was blocked by tetracaine, but the drug washed out before recovery, the rate was again 0.27 +/‐ 0.02 delta pHi h‐1 (n = 6). 3. In fibres first depolarized to about ‐23 mV in 50 mM‐K, constant [K] X [Cl] (recovery of 0.23 +/‐ 0.03 delta pHi h‐1, n = 6), and then repolarized to ‐79 mV in 2.5 mM‐K, the slow rate of recovery was the same (0.03 +/‐ 0.02 delta pHi h‐1) as that in fibres without a history of depolarization and thus of Ca release. 4. In fibres depolarized to ‐50 mV (15 mM‐K, constant Cl) and then exposed to caffeine (4 mM) which releases Ca from intracellular stores, the recovery was the same (0.07 +/‐ 0.03 delta pHi h‐1, n = 5) as in depolarized fibres not exposed to caffeine (0.09 +/‐ 0.01 delta pHi h‐1, n = 5). 5. We conclude that in frog muscle transient Ca release induced by either depolarization or caffeine does not affect the rate of subsequent pHi recovery. Tetracaine reversibly inhibits pHi recovery, but this inhibition is not due to its blocking of Ca release. 6. Recovery from CO2‐induced acidification of fibres depolarized to ‐21 mV in 50 mM‐K, constant Cl was halved, from 0.31 +/‐ 0.04 delta pHi h‐1 (n = 10) to 0.15 +/‐ 0.01 delta pHi h‐1 (n = 13), when external Ca was raised from 4 to 10 mM.(ABSTRACT TRUNCATED AT 400 WORDS)
Regulation of intracellular pH in reticulospinal neurones of the lamprey, Petromyzon marinus.
Authors: Chesler M
Published: December 2014

1. The regulation of intracellular pH (pHi) in lamprey reticulospinal neurones was investigated with pH‐sensitive micro‐electrodes based on a neutral carrier liquid membrane. Experiments were performed using an in vitro brain‐stem preparation. 2. In HEPES‐buffered solutions, extracellular pH (pHo) was consistently more acidic than the pH of the bathing solution (pHb). In HCO3(‐)‐buffered solutions, the brain was also relatively acidic, but the brain pH gradient was smaller. 3. In HEPES‐ and HCO3(‐)‐buffered solutions, mean pHi was 7.40‐7.50. This range was too high to be explained by a passive distribution of H+, OH‐ or HCO3‐. 4. In nominally HCO3(‐)‐free, HEPES‐buffered solution, cells were acid loaded by addition and subsequent withdrawal of NH4+ from the superfusate. pHi recovered from acid loading by an energy‐dependent process in 10‐20 min. Recovery from acid loading in HEPES‐buffered solutions was blocked by exposure to amiloride. 5. Removal of extracellular Na+ caused a slow, accelerating fall of pHi. Return of Na+ to the bath caused an immediate reversal of this acidification, followed by a slow recovery of pHi. Measurement with Na+‐sensitive micro‐electrodes during acid loading showed a rapid rise in the intracellular Na+ activity [( Na+]i). 6. Following acid loading, transition from HEPES‐ to HCO3(‐)‐buffered solutions caused an increase in the acid extrusion rate of at least 48%. The effect of these solution changes was dependent on pHo. After blocking pHi recovery with amiloride, transition from HEPES‐ to HCO3(‐)‐buffered Ringer plus amiloride produced a slow recovery of pHi. 7. Recovery from acid loading in HCO3(‐)‐buffered solutions was inhibited 65% by the anion transport blocker DIDS (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid). Recovery from acid loading after incubation in Cl(‐)‐free solution was slower than recovery after replenishment of Cl‐. 8. It is concluded that in HCO3(‐)‐free solutions, pHi regulation is accomplished by a Na‐H exchange mechanism. In the presence of extracellular HCO3‐ an additional mechanism can operate to extrude intracellular acid.
Relations between spinocervical and post‐synaptic dorsal column neurones in the cat.
Authors: Brown A G , Noble R , Riddell J S
Published: December 2014

1. In chloralose‐anaesthetized cats single‐unit micro‐electrode recordings were made at the lumbosacral level either from axons in the dorsolateral funiculus and dorsal columns, identified as belonging to the spinocervical tract (s.c.t.) or post‐synaptic dorsal column (p.s.d.c.) pathway respectively, or from neurones in the dorsal horn similarly identified. 2. Attempts were made to show that s.c.t. and p.s.d.c. neurones had axons that bifurcated, so that they sent branches into both the ipsilateral dorsolateral funiculus and the dorsal columns. That is, that some, or all, of the presumed s.c.t. or p.s.d.c. axons were common to both populations. In addition, the effects of stimuli applied to the ipsilateral dorsolateral funiculus at C3 and C1 on the resting discharges of p.s.d.c. neurones were examined in order to determine the effectiveness of the link between the s.c.t. and the p.s.d.c. pathway. 3. Thirty‐three s.c.t. units (twenty‐six axonal recordings and seven soma‐dendritic recordings) and thirty p.s.d.c. units (twenty‐four axonal and six soma‐dendritic recordings) were examined for bifurcating axons by electrically stimulating the dorsolateral funiculus at C3 and the dorsal columns at C4. None of the p.s.d.c. units could be antidromically activated from the ipsilateral dorsolateral funiculus with stimulus strengths up to 40 V or seventy times threshold for antidromic activation from the dorsal columns. Similarly, twenty s.c.t. units could not be activated antidromically from the dorsal columns at stimulus strengths up to 30 V or thirty times threshold for their antidromic excitation from the dorsolateral funiculus. Thirteen s.c.t. units were antidromically activated from the cervical dorsal columns, eight at seventeen or more times threshold for their activation from the dorsolateral funiculus and five at between two and nine times threshold. All s.c.t. units that were activated antidromically from both the cervical dorsal columns and the dorsolateral funiculus showed similar latencies for the two responses. 4. Twenty‐five p.s.d.c. units were examined for the effects of ipsilateral dorsolateral funiculus stimulation on their resting activity. In thirteen, clear evidence of facilitatory effects from C3 were observed, whereas similar results were seen in only six of these units when C1 was stimulated and the effects were less. The facilitation had a latency of 3‐16 ms and lasted for 6‐22 ms. In all but one of the twenty‐five units, stimulation at both C1 and C3 produced profound inhibition of the resting discharge that began at between 8 and 26 ms and lasted for up to 300 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic inputs to immunohistochemically identified neurones in the submucous plexus of the guinea‐pig small intestine.
Authors: Bornstein J C , Costa M , Furness J B
Published: December 2014

1. Electrophysiological recordings were made from neurones in the submucous plexus of the guinea‐pig small intestine, and these neurones were classified according to their synaptic inputs. 2. The neurones from which recording were made were filled during the recording period with the fluorescent dye, Lucifer Yellow, so they could be re‐identified after processing for immunohistochemical localization of vasoactive intestinal peptide (VIP). 3. The presence or absence of VIP‐like immunoreactivity was determined for a total of 130 neurones whose synaptic inputs had been fully characterized and eighty‐two were found to be VIP reactive. After the VIP reactivity had been assessed, the preparations were reprocessed to reveal immunoreactivity for neuropeptide Y (NPY) and a further twenty‐three neurones (none of which were reactive for VIP) were found to be reactive for this peptide. Of the remaining twenty‐five neurones, nineteen were not reactive for either VIP or NPY and six could not be re‐identified after reprocessing. 4. Electrical stimulation of internodal strands evoked excitatory synaptic potentials lasting 20‐30 ms (fast responses) in all but one of the 130 neurones studied. 5. Almost all the VIP‐reactive neurones (seventy‐eight of eighty‐two cells) exhibited inhibitory synaptic potentials, ranging in amplitude from 2 to 30 mV and lasting 150‐1500 ms, but few of the VIP‐negative neurones had such responses (six of forty‐eight cells). No inhibitory synaptic potentials could be evoked in any of the NPY‐reactive neurones. 6. Most VIP‐reactive neurones (sixty‐nine) had a slow excitatory synaptic potential which could be evoked by a single stimulus, lasted 5‐20 s and was associated with an increase in input resistance. Only one NPY‐reactive neurone had a slow excitatory potential, but such potentials were seen in nine of the nineteen VIP‐negative, NPY‐negative neurones. 7. In nine of the twenty‐three NPY‐reactive neurones a single stimulus evoked an excitatory synaptic potential (intermediate excitatory synaptic potential) lasting 500‐1500 ms and associated with a fall in the input resistance. None of the VIP‐negative, NPY‐negative neurones exhibited the intermediate excitatory potentials but it was not possible to determine whether such potentials could be evoked in VIP‐reactive neurones because the inhibitory synaptic potentials would obscure such events. 8. It is concluded that neurochemically distinct populations of submucous neurones can be distinguished physiologically on the basis of the differing combinations of types of synaptic input they receive.
The nature and origin of calcium‐insensitive miniature end‐plate potentials at rodent neuromuscular junctions.
Authors: Lupa M T , Tabti N , Thesleff S , Vyskocil F , Yu S P
Published: December 2014

1. To study the nature and origin of slow‐rising, Ca2+‐insensitive miniature end‐plate potentials (m.e.p.p.s) in mammalian muscle we used intracellular recording techniques and drugs which block acetylcholine (ACh) synthesis or the uptake of ACh into synaptic vesicles. Slow m.e.p.p.s were induced in vivo by paralysing the extensor digitorum longus muscle of the rat with botulinum toxin type A or in vitro by the application of 4‐aminoquinoline to the mouse diaphragm nerve‐muscle preparation. 2. Hemicholinium‐3, which blocks ACh synthesis, reduced the amplitude of all synaptic potentials including slow m.e.p.p.s, but only if the nerve was stimulated. 3. 2(4‐phenylpiperidino)cyclohexanol (AH‐5183), which blocks the active uptake of ACh into synaptic vesicles, reduced both the frequency and the amplitude of slow m.e.p.p.s and did so without requiring nerve stimulation. 4. No correlation was observed between the molecular leakage of ACh from the motor nerve and the frequency and amplitude of slow m.e.p.p.s. 5. We conclude that slow m.e.p.p.s are caused by the release of ACh from the nerve terminal, possibly from a small pool of synaptic vesicle‐like structures.
Calcium dependence of presynaptic calcium current and post‐synaptic response at the squid giant synapse.
Authors: Augustine G J , Charlton M P
Published: December 2014

1. Neurotransmitter release has a non‐linear dependence upon the external Ca concentration, [Ca]o. This may be due to a 'co‐operative' action of Ca in triggering release. The dependence of presynaptic Ca currents and post‐synaptic currents (p.s.c.s) upon [Ca]o was examined at voltage‐clamped 'giant' synapses of squid to determine whether this 'co‐operativity' occurs during or after influx of Ca into the presynaptic terminal. 2. Presynaptic Ca current was proportional to [( Ca]o/(1 + [Ca]o/KD]n, where n, the order of the function, was roughly 1 and KD, the apparent dissociation constant for Ca, was approximately 80 mM. 3. P.s.c.s also could be described by the same function, but had an n of 3‐4 and a lower KD. 4. These results suggest that the 'co‐operative' action of Ca occurs at a step or steps beyond entry of Ca into the presynaptic terminal. 5. Synaptic transfer curves relating presynaptic Ca currents, elicited by depolarizations to different potentials, to resultant p.s.c.s were power functions whose exponent depended upon [Ca]o. Maximum exponents were as high as 4 at [Ca]o of 3 mM. The dependence of these curves upon [Ca]o helps to explain why previous determinations, which were performed at a variety of [Ca]o levels, yielded a variety of transfer curve exponent values. 6. Transfer curves generated from responses to constant presynaptic depolarizations, with Ca current varied by [Ca]o changes, also were power functions with exponents of approximately 4. Thus p.s.c.s were high‐exponent power functions of Ca current regardless of whether Ca current was modified by changes in membrane potential or in [Ca]o.
Transcellular sodium fluxes and pump activity in Necturus gall‐bladder epithelial cells.
Authors: Hill A E , Hill B S
Published: December 2014

1. Transepithelial Na transport in Necturus was determined by measuring the rate of isotonic fluid flow. The rate at 20 degrees C was equivalent to 175 pmol cm‐2 s‐1. 2. Ouabain was effective in Necturus, binding to the Na pump in gall‐bladder cells with a mean rate constant of 5.4 X 10(3) M‐1 s‐1. Measurement of the diffusive time constant of the free space for [3H]ouabain shows that the pump must be fully inhibited within 20 s when ouabain is applied to the serosa at 10(‐3) M. 3. The serosal Na efflux from loaded cells was inhibited 36% by ouabain equal to a flux of 73 pmol cm‐2 s‐1. The remaining flux could not be attributed to either exchange diffusion or electrodiffusion induced by ouabain. 4. The transepithelial potential was 0.3 mV serosa positive. The short‐circuit current measured was 6.33 +/‐ 1.9 microA cm‐2, equal to a positive univalent ion flux of 65.6 pmol cm‐2 s‐1 or 38% of the net Na transfer. The current was inhibited within 1‐5 min by 5 X 10(‐5) M‐amiloride. 5. Fluid secretion was immediately inhibited 34% by ouabain, equivalent to an isotonic transport of Na of 59.7 pmol cm‐2 s‐1. Thereafter it continued for at least an hour, sometimes declining slowly. Amiloride had little effect (13%). 6. The Na pump rate was measured by titrating the cell content with tracer Na at different times after ouabain treatment. The initial slope was equal to a rate of 61.6 pmol cm‐2 s‐1 or 35% of the net flux at time zero. 7. The Na pump rate has also been measured by recording the rise in cell Na activity with ion‐specific micro‐electrodes, and correcting for swelling effects. The Na pump rate was very similar to that estimated from the rise in tracer Na content, equal to 59.3 pmol cm‐2 s‐1 or 31.4% of the transepithelial rate. Examination of the same experiment in the literature shows a closely similar value, about one‐third of that expected from fluid secretion or net flux measurements. 8. A scheme is proposed to explain the results, which requires a flow of NaCl through a parallel pathway of small Na content involving exchange en route with the cytoplasmic Na.
Control of cell volume and ion transport by beta‐adrenergic catecholamines in erythrocytes of rainbow trout, Salmo gairdneri.
Authors: Borgese F , Garcia-Romeu F , Motais R
Published: December 2014

1. Trout red cells suspended in an isotonic medium containing beta‐adrenergic catecholamines or adenosine 3',5'‐phosphate (cyclic AMP) enlarge rapidly to reach a new steady‐state volume which is maintained as long as hormone is present. The volume response is not changed by inhibition of the Na+‐K+ pump with ouabain. The new steady‐state volume was shown to result from a dynamic equilibrium involving the simultaneous functioning of two regulatory processes induced by hormone: a volume increase response that causes cells to enlarge by gaining Na+ and a volume decrease response that causes cells to shrink by losing K+. 2. As previously described, the volume increase response due to NaCl entry, is mediated by the activation by cyclic AMP of a Na+‐H+ antiport operating in parallel to Cl(‐)‐OH‐ exchanges. In addition, it is shown in this paper that the Na+ uptake is a discontinuous, oscillatory process and that NaCl entry continues for several hours, i.e. as long as hormone is present. 3. The volume decrease response involves a passive, Cl(‐)‐dependent K+ loss. Na+ cannot use this pathway. The response is blocked by replacement of Cl‐ by NO3‐, by loop diuretics (furosemide, bumetanide) but also by inhibitors of the anion exchanger (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS), niflumic acid). The activation of this ouabain‐insensitive, Cl(‐)‐dependent K+ transport system is not directly triggered by cyclic AMP. It involves an all‐or‐none type of switching phenomenon which occurs when the cells swell to a certain volume. Thus it is a regulatory response to the increase in cell volume induced by stimulation of the Na+‐H+ exchange by cyclic AMP. Inactivation is also volume dependent: when the cell size approaches the initial size the pathway shuts off. Thus the controlling mechanism of the K+ pathway acts like a reversible on‐off switch that operates around a given volume. Ca2+ was not found to be involved in this control. Cyclic AMP is not necessary to keep the activated K+ pathway open but it could be one of the factors involved in the activating process. 4. There are several lines of evidence indicating that in trout red cells the volume decrease and the volume increase responses may not be brought about by the same transport mechanism operating in different modes. The movements of Na+, K+ and Cl‐ account for the water movements during volume increase and decrease. Thus movements of other solutes such as amino acids need not be considered.
An intracellular study of spinocervical tract cell responses to natural stimuli and single hair afferent fibres in cats.
Authors: Brown A G , Koerber H R , Noble R
Published: December 2014

1. Intracellular recordings were made from spinocervical tract (s.c.t.) neurones in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. In one series of experiments the cells' receptive fields were examined with the use of natural stimuli. Hair movement within the impulse firing zone of the cell evoked excitatory post‐synaptic potentials (e.p.s.p.s) from which impulses were generated; in addition, in the majority of s.c.t. cells tested, areas were found within the impulse firing zone where hair movement elicited both e.p.s.p.s and inhibitory post‐synaptic potentials (i.p.s.p.s). Outside the firing zones, both regions evoking e.p.s.p.s and regions evoking i.p.s.p.s were observed in all neurones examined in detail (ten cells). The responses of these neurones to a variety of natural stimuli showed the receptive fields of s.c.t. cells to be more complex than previously thought. 3. In a second series of experiments, intracellular recordings from s.c.t. cells were combined with intracellular recording and stimulation of single dorsal root ganglion cells belonging to group II hair follicle afferent fibres. When the afferent fibres innervated skin within the impulse firing zone of the s.c.t. cell, single afferent impulses evoked e.p.s.p. complexes consisting of both mono‐ and polysynaptic components; no i.p.s.p.s were observed in response to single hair follicle afferent impulses or to trains. Although the monosynaptic e.p.s.p. component was often large and had a fast rise time, s.c.t. cell impulses usually arose from the later components. Afferent fibres innervating the central region of the s.c.t. cell firing zones tended to evoke relatively large e.p.s.p.s with fast rise times. The rise times and amplitudes of the e.p.s.p.s evoked by afferent fibres from the periphery, however, varied between afferent fibres but included the slowest and smallest in the total sample of synaptically coupled pairs. Afferent fibres from outside the s.c.t. cell's firing zone were usually ineffective in setting up post‐synaptic potentials, but one group III hair follicle afferent fibre, from an inhibitory receptive field component, gave rise to i.p.s.p.s. 4. The effects of pairs and trains of afferent impulses at intervals of 10, 25, 50, 100 and 200 ms were examined. At 25 ms the response to the second afferent impulse was profoundly less than that evoked by the first and was still substantially reduced at 200 ms interval. In all synaptically coupled pairs studied, the e.p.s.p. complex evoked by the second afferent impulse was smaller in amplitude than that evoked by the first.(ABSTRACT TRUNCATED AT 400 WORDS)