bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of calcium channels in rat clonal pituitary cells with patch electrode voltage clamp
Authors: Hagiwara Susumu , Ohmori Harunori 
Published: December 2014

1. The properties of the Ca channel in tissue cultured clonal cells (GH3) isolated from a rat anterior pituitary tumour were studied with the patch electrode voltage‐clamp technique.2. To isolate the current through the Ca channel, the currents through the Na channel, the delayed K channel and the Ca2+ induced K channel were minimized by replacing the external Na+ with TEA+ and adding EGTA to the K‐free solution inside the patch electrode.3. The selectivity ratios through the Ca channel with different cations were 2·7 (Ba2+):1·6 (Sr2+):1·0 (Ca2+) and the m2 form of the activation kinetics and the relationships between the time constant and the membrane potential were common to the three divalent cations.4. The amplitude of the Ba2+ current increased linearly with [Ba2+]o up to 25 mM and thereafter tended to show saturation.5. The current—voltage relation showed a positive shift along the voltage axis as [Ba2+]o increased, probably due to the screening effect of Ba2+ on the negative surface charges.6. The time constant of activation as a function of the membrane potential showed a parallel shift as [Ba2+]o was increased, suggesting that the activation kinetics were independent of the permeant ion concentration.7. The time constant of the tail current was consistent with m2 kinetics for opening and closing of the Ca channel.8. The extrapolated ‘instantaneous’ tail current rapidly increased as the activating membrane potential became more positive and reached an apparent saturation at membrane potentials substantially more positive than the potential that gave the maximum peak inward current, and suggested that the single channel has a sigmoidal current—voltage relationship.9. The power density spectrum obtained during the steady‐state inward Ba2+ current had a cut‐off frequency which was nearly voltage independent; this is expected if the fluctuation of the current originates from m2 activation kinetics.10. The results of noise analysis suggest that the amplitude of the single Ca channel current was about 0·2 pA at 25 mM‐Ba2+ and 0·7 pA at 100 mM‐Ba2+ for membrane potentials in the vicinity of the maximum inward current.
Role of cyclic adenosine monophosphate in amylase release from dissociated rat pancreatic acini
Authors: Singh Manjit 
Published: December 2014

1. The effect of octapeptide of cholecystokinin‐pancreozymin (CCK8), bethanechol, cholera toxin, glucagon and vasoactive intestinal polypeptide (VIP) on amylase secretion and lactic dehydrogenase (LDH) release from isolated rat pancreatic acini was studied.2. In isolated rat pancreatic acini, in the absence of theophylline in the medium, amylase secretion was increased by 65‐78% with 10−7 and 10−6 M‐cholera toxin. In the presence of theophylline, amylase secretion was increased by 43‐56% with 10−7 and 10−6 M‐cholera toxin following a 90 min incubation. No effect was observed in the presence of theophylline at 30 and 60 min. The effect of cholera toxin was potentiated by CCK8 at 60 and 90 min.3. In the absence of theophylline in the medium, amylase secretion was increased by 81‐118% with 10−5 and 10−4 M‐glucagon and 86% with 10−6 M‐VIP at 60 min. In the presence of theophylline in the medium, amylase secretion was increased by 53‐246% with 10−9 to 10−6 M‐glucagon and 111‐158% with 10−7 and 10−6 M‐VIP respectively. The effect of glucagon and VIP was potentiated by CCK8.4. Potentiation of the rate of amylase release due to glucagon (10−5 M) and VIP (10−6 M) occurred during the first 15 min of incubation.5. Release of LDH was not increased by any of these agents.6. It is concluded that cyclic AMP rise (due to cholera toxin, glucagon and VIP effect) increased amylase secretion from rat pancreatic acinar cells. This effect is less marked than in the guinea‐pig pancreas and is potentiated by agents mobilizing cellular Ca2+ (CCK8 and bethanechol).7. These data indicate species‐specific variation in the action of cyclic AMP in the pancreas.
Origin and sensitivity of the light peak in the intact cat eye
Authors: Linsenmeier Robert A. , Steinberg Roy H. 
Published: December 2014

1. The light peak is a large light‐induced change in the DC potential across the eye (standing potential) that reaches its maximum in 5‐13 min in mammals. The light peak of the intact cat eye was studied in order to define its cellular origin and stimulus—response characteristics. Direct‐coupled recordings were made with a vitreal electrode and also with intraretinal and intracellular micro‐electrodes. Light peaks were generally evoked with 300 sec periods of diffuse white illumination.2. Micro‐electrode recordings made in the subretinal space just outside the apical membrane of the retinal pigment epithelium (r.p.e.) showed that the light peak was a change in trans‐epithelial potential. No component was generated in the neural retina.3. Intracellular recordings from r.p.e. cells showed that the change in trans‐epithelial potential resulted from a depolarization of the basal membrane (facing the choroid). This depolarization came after the hyperpolarization of the apical membrane that gave rise to the r.p.e. component of the c‐wave of the e.r.g.4. The light peak amplitude at a constant retinal illumination was nearly linear with stimulus duration over the range 15‐180 sec, and saturated at about 300 sec. The time‐to‐peak remained nearly constant at about 300 sec over this range. Large light peaks could be evoked with flashes as short as 10 sec if the retinal illumination was several log units above rod saturation.5. When stimulus duration was held constant at 300 sec, light peak amplitude was graded with illumination over a wide range, from 3 log units below to 2 log units above rod saturation. The threshold of the light peak was below that of the e.r.g. and only about 1·5‐2·5 log units above the absolute threshold of the most sensitive ganglion cells. The increase of light peak amplitude above rod saturation was not due primarily to cones.6. The trans‐epithelial light peak had an unusual dependence on stimulus area, being at least twice as large in response to diffuse light as it was in response to a large spot (10 deg diameter) of the same retinal illumination.7. These findings indicate that the light peak represents a normal physiological interaction between the retina and the r.p.e. They also suggest that the interaction involves a change in the concentration of a diffusible substance in the retina, which then either enters the r.p.e. itself, or triggers an internal messenger to cause the basal depolarization.
Histochemical and physiological properties of cat motor units after self‐ and cross‐reinnervation
Authors: Chan A. K. , Edgerton V. R. , Goslow G. E. , Kurata H. , Rasmussen S. A. , Spector S. A. 
Published: December 2014

1. This report describes selected histochemical and physiological properties of the motor units of adult cat soleus muscle approximately one year after self‐ and cross‐reinnervation with the nerve of the heterogenous flexor hallucis longus (f.h.l.). Self‐reinnervated f.h.l. motor units are also considered. Whole muscles were tested for fibre reaction to alkaline pre‐incubated ATPase, α‐glycerophosphate dehydrogenase (α‐GPD) and reduced nicotinamide adenine dinucleotide diaphorase (NADH‐D). Motor units were isolated and studied by splitting the ventral root in acute preparations.2. The histochemical fibre type profile in the self‐reinnervated muscle was comparable to normal muscle as was mean twitch contraction time, twitch—tetanus ratio and fatigue index. The mean tetanic tension of the soleus self‐ and cross‐reinnervated motor units appeared close to a normal soleus whereas the mean tetanic tension of the f.h.l. self‐reinnervated units was significantly less than a normal f.h.l.3. An average of 14% of the fibres of the soleus cross‐reinnervated muscles had high ATPase and a α‐GPD staining intensity in contrast to normal and self‐reinnervated soleus in which such fibres are absent. Thus alkaline lability of myofibrillar ATPase increased in some fibres of what was originally a homogeneous population. The small increase in the number of densely staining fibres for ATPase at an alkaline pH (14%) was associated with a 73% decrease in (mean) contraction time (41 ± 11 ms) of the thirty‐three cross‐reinnervated muscle units studied, with no unit's contraction time greater than 60 ms. Mean contraction times for the self‐reinnervated soleus and f.h.l. muscles were 78 ± 31 ms and 27 ± 8 ms respectively.4. All fibres of the soleus cross‐reinnervated muscles showed intense reaction to NADH‐D, as was true of self‐reinnervated soleus. This staining pattern is typical of normal soleus. In concordance, these motor units consistently demonstrated a high resistance to fatigue when stimulated for a four‐minute period.5. These results suggest that in the adult self‐and cross‐reinnervated soleus muscle, there is some active mechanism which regulates the eventual size of motor units as reflected by tetanic tension.6. Change in contraction time from that typical for a soleus unit to that similar to an f.h.l. unit remains incomplete one year after cross‐reinnervation. Within this time this partial change in single motor units reflects incomplete neural control of this property rather than a mixture of self‐ and foreign‐innervation.7. A greater degree of independence from neural control to conversion of the histochemically demonstrated myofibrillar ATPase activity exists than is the case for contraction time.
Effects of hypoxia on catecholamine synthesis in rabbit carotid body in vitro
Authors: Fidone S. , Gonzalez C. , Yoshizaki K. 
Published: December 2014

1. Unanaesthetized, unrestrained rabbits were exposed for 3 hr in a chamber to either air, hypoxic gas mixtures (10% or 14% O2 in N2) or a hyperoxic gas mixture (50% O2 in N2). The carotid bodies were then removed and incubated for 3 hr in modified Tyrode media equilibrated with 100% O2 and containing either [3H]tyrosine or [3H]DOPA. The contents of [3H]DA and [3H]NA in the tissue were determined as described in the preceding paper.2. When [3H]DOPA was used as precursor, neither labelled dopamine (DA) or noradrenaline (NA) synthesis was increased in carotid bodies from rabbits exposed to 10% O2 in N2. Following exposure to 10% O2 in N2 and incubation with [3H]tyrosine, however, [3H]DA synthesis was increased by 72% above control (air) values while [3H]NA synthesis was unchanged. Less severe hypoxia, 14% O2 in N2, resulted in a smaller increase in [3H]DA synthesis, i.e. 53% above control value. Again, [3H]NA synthesis was unchanged. Similar experiments with the superior cervical ganglion involving exposure of the animals to either 10% or 14% O2 in N2 did not produce any change in the amounts of [3H]DA or [3H]NA synthesized from [3H]tyrosine when compared to control animals breathing air.3. Sympathectomy of the carotid body or transection of the carotid sinus nerve 12‐15 days prior to hypoxic exposure (10% O2 in N2) did not alter the increase in [3H]DA synthesis compared to normally innervated carotid bodies.4. Carotid bodies incubated with [3H]tyrosine for 2 hr in an alternating O2/N2 sequence (5 min in media equilibrated with 100% O2 followed by 3 min in media equilibrated with 100% N2) synthesized 37% more [3H]DA than control carotid bodies similarly exposed to an alternating O2/O2 sequence. [3H]NA synthesis was unchanged. However, tissue levels of non‐metabolized [3H]tyrosine were reduced by 19% in the carotid bodies exposed to the O2/N2 sequence.5. Exposure of rabbits for 3 hr to 50% O2 in N2, followed by incubation of their carotid bodies in [3H]tyrosine, resulted in a 19% decrease in the absolute value for [3H]DA synthesis compared to control carotid bodies, but this difference was not significant (P > 0·05). However, [3H]NA synthesis was significantly reduced (51%; P < 0·05) in the hyperoxic carotid bodies. Similar experiments with the superior cervical ganglion showed that [3H]DA and [3H]NA synthesis were unchanged under control vs. hyperoxic conditions.6. Carotid bodies incubated with [3H]tyrosine for 3 hr, then transferred for 1 hr to unlabelled media equilibrated with 10% O2 in N2, released 81% more [3H]DA, and contained 38% less [3H]DA, than similarly treated carotid bodies exposed to 100% O2. [3H]NA was not detectable in the media, and tissue levels of [3H]NA were the same in both hypoxic and control carotid bodies.
Effects of low oxygen on the release of dopamine from the rabbit carotid body in vitro
Authors: Fidone S. , Gonzalez C. , Yoshizaki K. 
Published: December 2014

1. Rabbit carotid bodies were pre‐loaded with [3H]dopamine (DA) synthesized from [3H]tyrosine and then mounted in a vertical drop‐type superfusion chamber which permitted simultaneous collection of released [3H]DA and recording of chemoreceptor discharge from the carotid sinus nerve.2. The time course of the spontaneous release of [3H]DA (superfusion with media equilibrated with 100% O2) in the presence of monoamine oxidase inhibitors exhibited two linear components, an initial steep phase followed after 3‐4 hr by a later slower phase of release.3. When a 5 min low O2 stimulus was delivered during the initial steep linear component of resting [3H]DA release, there was an abrupt increase in release, the magnitude of which was stimulus‐dependent.4. The efflux of total radioactivity from the preparation declined exponentially with time; under resting conditions it was principally non‐metabolized [3H]tyrosine. During stimulation, however the efflux increased, and 60‐80% of the radioactivity could be attributed to [3H]DA.5. For a given low O2 stimulus, the ratio of [3H]DA release during the stimulus period over that in the preceding control period remained approximately the same throughout a single experiment. Ratios for different low O2 stimuli (50, 40, 30, 20, 10 and 0% O2 in N2) yielded a parabolic relationship when plotted against stimulus intensity.6. Transection of the carotid sinus nerve or removal of the superior cervical ganglion 12‐15 days prior to the experiment did not affect the release of [3H]DA at moderate stimulus intensities (superfusion with media equilibrated with 30% or 10% O2 in N2) but both procedures significantly depressed release at the highest stimulus intensity (100% N2).7. Chemoreceptor discharge and [3H]DA release were simultaneously monitored in experiments using superfusion media free of monoamine oxidase inhibitors. In these experiments, the efflux of [3H]dihydroxyphenyl acetic acid (DOPAC) was also measured. The increase in peak chemosensory discharge was closely correlated with the increase in total release ([3H]DA + [3H]DOPAC) during stimulation with a series of low O2 stimuli.8. Release of [3H]DA was almost completely abolished during superfusion with Ca2+‐free, high Mg2+ (2·1 mM) media, and the stimulus‐related efflux of [3H]DOPAC was significantly reduced. However, chemoreceptor discharge was diminished by only 55%. These data are discussed with respect to their implications for DA as a chemosensory transmitter in rabbit carotid body.
Free magnesium in sheep, ferret and frog striated muscle at rest measured with ion‐selective micro‐electrodes
Authors: Hess P. , Metzger P. , Weingart R. 
Published: December 2014

1. Neutral carrier‐based liquid membrane micro‐electrodes were constructed which are suitable for continuous measurements of [Mg2+]i in cardiac and skeletal muscle preparations.2. The electrodes show a Nernstian behaviour in pure MgCl2 solutions. In the presence of a constant ionic background chosen to simulate the cytoplasmic composition, the calibration function flattens progressively with lower [Mg2+], due to the interference of K+ and Na+. The response to changes in [Mg2+] is less than 0·5 sec.3. In quiescent preparations at room temperature (23 °C), the following basal [Mg2+]i were determined: 3·5 mM (sheep Purkinje fibres), 3·1 mM (sheep ventricular muscle), 3·0 mM (ferret ventricular muscle) and 3·3 mM (frog skeletal muscle).4. In cardiac tissue, electrical stimulation does not measurably affect the basal [Mg2+]i.5. In the presence of 0·5 mM‐Mg2+o, the calculated Mg2+ equilibrium potentials, EMg, are in the range of ‐23 to ‐25 mV, suggesting that Mg2+ is not passively distributed across the sarcolemma in striated muscle.6. Further studies were performed on sheep Purkinje fibres to investigate the effect of various experimental interventions on [Mg2+]i.7. Elevating [Mg2+]o from 0·5 to 10 mM resulted in a reversible increase of [Mg2+]i. The initial rate of increase corresponds to a Mg2+ influx of 0·42 p‐mole/cm2.sec, or a magnesium permeability, PMg, of 1·6 × 10−8cm/sec.8. Increasing PCO2 from nominally 0 to 100 mmHg (Tris‐buffered vs. bicarbonate‐buffered Tyrode solution) produced a reversible decrease in [Mg2+]i by roughly 0·45 mM, probably due to Mg2+ binding the newly formed intracellular HCO3−.9. The effect of metabolic poisoning on [Mg2+]i was assessed by exposure to cyanide, iodoacetic acid and 2‐4‐dinitrophenol. No significant increase in [Mg2+]i indicative of a liberation of Mg2+ from ATP was observed.
Properties of junctional and extrajunctional acetylcholine‐receptor channels in organ cultured human muscle fibres
Authors: Cull‐Candy S. G. , Miledi R. , Uchitel O. D. 
Published: December 2014

1. Current noise, obtained during steady ionophoretic application of acetylcholine (ACh) to voltage‐clamped human fibres has been analysed to derive properties of end‐plate channels and also extrajunctional ACh‐activated channels which are present at the muscle—tendon junction of normal fibres. In addition, ACh‐receptor channels present at the end‐plate and tendon region in organ cultured muscles have been compared with those in fresh muscles.2. Extrajunctional channels in the tendon region of fresh fibres have a longer mean life‐time, τ, and a smaller single channel conductance, γ, than the junctional channels. τ was 1·71 ±0·11 msec and γ was 25·05 ± 1·18 pS for junctional channels; τ was 3·16 ± 0·33 msec and γ was 12·76 ± 1·29 pS for extrajunctional channels.3. Properties of channels in the end‐plate and tendon region were unchanged during short‐term (< 7 days) organ culture at 23 or 36 °C. The voltage sensitivity of the mean channel life‐time was similar at junctional and extrajunctional sites.4. In muscles organ cultured for 7 days at 36 °C, double component noise spectra were obtained at some end‐plates. The fast and slow time constants underlying the noise appeared to correspond to simultaneous activation of junctional and extrajunctional channels.5. After organ culture for 3‐4 weeks at 23 °C the mean life‐time of the end‐plate channels was prolonged while their single channel conductance was unchanged, τ = 3·58 ± 0·16 msec; γ = 22·11 ± 0·83 pS (Vm = ‐80 mV, T = 21 °C).6. As end‐plate channel properties were unchanged in short‐term cultures it was possible to assess post‐junctional sensitivity by comparing miniature end‐plate current (m.e.p.c.) amplitudes in both normal and myasthenia gravis affected muscles. No evidence was found for a change in post‐synaptic sensitivity during organ culture at 23 °C of normal or myasthenia gravis muscle fibres, which seems to rule out reversible block of receptors by anti‐receptor antibody as playing an important role in myasthenia gravis.
The pCa‐tension and force‐velocity characteristics of skinned fibres isolated from fish fast and slow muscles
Authors: Altringham J. D. , Johnston I. A. 
Published: December 2014

1. Single fast fibres and small bundles of two to six slow fibres were dissected from the myotomal muscles of the cod, Gadus morhua, and the dogfish, Scyliorhinus canicula. Fibres were chemically skinned with the non‐ionic detergent Brij 58.2. The isometric tension properties were investigated. Maximal isometric tensions (mean ± S.E. of mean) were 18·65±1·18 (n = 11) and 8·34±0·98 (n = 13) N cm−2 for cod fast and slow fibres, and 18·34±0·88 (n = 28) and 8·24±0·39 (n = 12) N cm−2 for dogfish fast and slow fibres respectively. The values are comparable to those observed in mammalian and amphibian skinned fibres. The lower tensions generated by the slow fibres cannot be fully explained on the basis of their lower myofibrillar fractional volume.3. In common with previous studies, a steep sigmoid relationship between pCa and tension was observed. The threshold for tension generation was around pCa 7·2. Half‐maximal pCas were 6·08 and 6·42 for cod fast and slow muscle, and 6·41 and 6·50 for dogfish fast and slow fibres respectively. Cod fibres were maximally activated at around pCa 5·18, and dogfish fibres at pCa 5·62.4. Contraction‐induced residual tensions were observed in cod fast fibres after return to relaxing solution. This phenomenon is a feature common to many skinned fibre studies, but the mechanism behind it has yet to be resolved.5. The force‐velocity characteristics of fast and slow fibres have been investigated (at 8 °C).6. Points below 0·6 P0 on the P-V curves could be fitted to a linear form of the Hill equation. Extrapolated Vmaxs were calculated as follows: cod fast fibre Vmax = 1·01 muscle length sec−1 (Lsec−1) (a = 0·21 P0; b = 0·21 Lsec−1). Slow fibre = 0·53 Lsec−1 (a = 0·28P0; b = 0·21 Lsec−1). Dogfish fast fibre Vmax = 2·34 Lsec−1 (a = 0·06 P0; b = 0·14 Lsec−1). Slow fibre = 0·67 Lsec−1 (a = 0·19 P0; b = 0·13 Lsec−1).7. Contraction velocity in cod slow fibres decreased continuously to produce markedly non‐linear velocity transients, similar to those reported for amphibian slow fibres.8. The effect of altering Ca2+ concentration on the shape of the isotonic velocity curve (at low loads) was studied in dogfish fast fibres (0·5‐1 °C). Contraction velocity decreased continuously during shortening, at both maximal and half‐maximal Ca2+ concentration. The rate of decay of velocity with shortening was greater at low Ca2+ concentration.
The thermoregulatory effects of noradrenaline, serotonin and carbachol injected into the rat spinal subarachnoid space
Authors: Lopachin Richard M. , Rudy T. A. 
Published: December 2014

1. We have examined the effects on thermoregulation in the rat of noradrenaline bitartrate (NA), 5‐hydroxytryptamine hydrochloride (5‐HT) and carbamylcholine chloride (CCh) injected into the lumbar spinal subarachnoid space via a chronic indwelling catheter.2. Intrathecal injections of the monoamines and CCh reproducibly affected thermoregulation, whereas injections of control solutions had no effect.3. Intrathecal injections of NA (0·01‐0·30 μmol) produced a dose‐dependent hypothermia associated with a decrease in tail skin vasomotor tone. Shivering activity was not depressed during the hypothermia and sometimes increased. Intrathecal administration of the α‐adrenergic agonist clonidine (0·0175‐0·070 μmol) elicited changes in Tc and Tsk similar to those induced by intrathecal NA.4. Intrathecal 5‐HT (0·030‐0·90 μmol) elicited a dose‐dependent hyperthermia accompanied by increased tail skin vasomotor tone and increased shivering.5. CCh injected intrathecally (0·001‐0·06 μmol) evoked a dose‐dependent hyperthermia. During the period when core temperature was rising, tail skin vasomotor tone increased and shivering‐like activity was present. Once the maximum core temperature had been reached, tail skin vasodilatation occurred. Vasodilatation persisted until core temperature had returned to normal.6. Intravenous injections of 5‐HT (0·30 and 0·90 μmol) or CCh (0·006 and 0·03 μmol) caused no thermoregulatory effect. The effects of these agents injected intrathecally were therefore not due to an action in the periphery.7. Intravenous infusions of NA (0·06 and 0·10 μmol) produced hypothermia and transient tail skin vasodilatation. We suggest that an action at peripheral sites may have contributed to the effects produced by intrathecal injection of this monamine.8. These findings suggest that spinal noradrenergic, serotonergic and cholinergic synapses may be importantly involved in the control of body temperature in the rat. The possible functional roles of these synapses and the putative spinal sites of action of the injected substances are discussed.