bluuebunny/crossref_metadata_2025 huggingface dataset:
Short‐latency inhibition of soleus motoneurones by impulses in Ia afferents from the gastrocnemius muscle in humans.
Authors: Gritti I , Schieppati M
Published: December 2014

1. The possibility that the Ia afferent fibres from the gastrocnemius medialis muscle could be responsible for a decrease in excitability of the soleus motor pool was investigated. 2. The soleus H reflex, evoked by tibial nerve stimulation in the popliteal fossa, was conditioned by a single stimulus to the gastrocnemius medialis nerve at various stimulus intensities and conditioning‐test intervals. Care was taken to avoid spread of current from the conditioning stimulus to the tibial nerve, and the results obtained by surface stimulation were compared with those obtained by stimulation through a needle whose tip was positioned closer to the nerve. 3. Stimulation of the gastrocnemius medialis nerve induced two short‐lasting periods of inhibition in the soleus H reflex, peaking at about 0 and 5 ms of conditioning‐test delay. The early inhibition could begin at a stimulus strength as low as 0.5 x MTh (the Motor Threshold). The later inhibition appeared on greater stimulus strength than the earlier. 4. Prolonged vibration of the Achilles tendon abolished the capability of the conditioning stimulus to induce the short‐latency inhibition of the soleus H reflex. 5. By stimulating the gastrocnemius medialis nerve at two points separated by a known distance, the conduction velocity of the fibres responsible for the early inhibition was estimated, and found to be around 100 m s‐1. 6. Isometric leg flexion, accomplished by tonic activation of gastrocnemius medialis and lateralis but not soleus, was able to induce an inhibition of the soleus H reflex even at very low levels of gastrocnemius electromyographic activity. 7. These findings strongly suggest the existence of an inhibitory effect of primary spindle afferent fibres from the gastrocnemius medialis muscle onto the soleus motor pool. This is not unexpected, since the gastrocnemius medialis muscle can be either agonist or antagonist to the soleus muscle in the performance of different movements.
A novel calcium‐dependent chloride current in Xenopus oocytes injected with brain messenger RNA.
Authors: Gillo B , Landau E M , Moriarty T M , Roberts J L , Sealfon S C
Published: December 2014

1. Membrane currents were studied in voltage‐clamped Xenopus laevis oocytes which had been injected with total rat brain RNA. 2. When the membrane potential was stepped from ‐100 to +10 mV, two components of outward current were observed which were named Tout1 and Tout2. 3. Both Tout1 and Tout2 were eliminated in chloride‐free or calcium‐free media and blocked by 9‐anthroic acid, indicating that they represented calcium‐dependent chloride currents. 4. Both currents were dependent on extracellular calcium (1.8‐10 mM), with Tout1 showing a greater sensitivity to changes in calcium concentration. 5. Tout2 but not Tout1 was blocked by intracellular injection of 300‐600 pmol, BaCl2 (final concentration in the oocyte: 0.3‐0.6 mM). Injection of KCl had no effect on either Tout1 or Tout2. 6. Tout2 but not Tout1 was enhanced by low concentrations of serotonin (0.5‐2 nM). This effect was blocked by 0.1 microM‐mianserin. Higher concentrations (above 10 nM) of serotonin decreased the amplitude of Tout2. The effect of serotonin was blocked by the protein kinase inhibitor, H‐7 (25 microM). 7. Tout2 but not Tout1 was enhanced by 10 nM‐phorbol myristate acetate. Higher concentrations of the phorbol ester decreased the amplitude of Tout2. 8. It is concluded that in oocytes injected with RNA there is an induction of a novel component of the calcium‐induced chloride current (Tout2). This current reflects a second process of chloride channel opening which can be enhanced by serotonin via activation of protein kinase C.
Sodium and potassium conductances in somatic membranes of rat Purkinje cells from organotypic cerebellar cultures.
Authors: Gähwiler B H , Llano I
Published: December 2014

1. The somatic voltage‐gated conductances of Purkinje cells in organotypic cultures (Gähwiler, 1981) were studied using the outside‐out patch recording configuration of the patch‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). 2. When activated by step depolarizations, the tetrodotoxin‐sensitive voltage‐dependent Na+ current presented two distinct phases: an initial surge of inward current fluctuations which activates rapidly upon pulse onset and decays within 20‐40 ms, and a later phase in which discrete bursts of single‐channel activity are interspersed with silent periods. 3. Ensemble fluctuation analysis of the current fluctuations during the early phase of the Na+ current and measurements of single channels during both early and late phases indicate that a single type of Na+ channel can account for both phases of the Na+ current. This channel has an elementary current amplitude of ‐2 pA at ‐40 mV. This amplitude did not vary significantly between ‐60 and ‐20 mV. The mean open time depended on membrane potential, increasing by a factor of three between ‐60 and ‐20 mV. 4. The early component of the Na+ current activated at a threshold of ‐60 mV and reached its maximum amplitude at ‐20, mid‐point for the activation curve being ‐40 mV. Times‐to‐peak current decreased with membrane potential, from 3.5 ms at ‐60 mV to 0.3 ms at 0 mV. The decay phase of the current presented two exponential components, with time constants of 1.5 and 10 ms at ‐40 mV. The steady‐state inactivation curve had a mid‐point at ‐75 mV. 5. The late component of the Na+ current was observed in the voltage range from ‐60 to ‐20 mV, with a maximum at ‐40 mV. Its maximum amplitude corresponded to approximately 1.7% of the peak amplitude of the early component. 6. Macroscopic potassium currents were observed upon step depolarizations above a threshold of ‐30 mV. The currents activated in a voltage‐dependent fashion, times‐to‐peak decreasing with depolarization, and partially inactivated during 40 ms depolarizing steps. Peak current amplitudes at any given membrane potential were decreased by depolarizing the holding potential. The macroscopic properties of the K+ current varied from patch to patch. 7. Two types of single‐channel K+ currents were observed during steady‐state depolarizations. The unitary current amplitudes were 2.7 and 10.4 pA at 30 mV, corresponding to chord conductances of 28 and 90 pS respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
Membrane currents elicited by divalent cations in Xenopus oocytes.
Authors: Miledi R , Parker I , Woodward R M
Published: December 2014

1. Membrane currents were recorded from voltage‐clamped Xenopus oocytes in response to bath application of various divalent cations. 2. In oocytes from 93 of 160 frogs tested, Co2+ ions evoked slow, oscillatory membrane currents. Sensitivity to Co2+ varied greatly between oocytes from different frogs, but was relatively consistent for oocytes taken from the same ovary. Oocytes with high sensitivity had response thresholds of 5‐10 microM, and gave currents greater than 1 microA to 1 mM‐CoCl2. In contrast, oocytes from some frogs gave no oscillatory response even to 10 mM‐CoCl2. With responsive oocytes, Cd2+, Ni2+, Zn2+, Mn2+ and Cr2+ ions (5 microM to 1 mM) also elicited oscillations, whereas Sr2+, Ba2+ and Ca2+ (0.1‐10 mM) showed very little activity, and Mg2+ ions, none. 3. Responses to divalent cation were well preserved in defolliculated oocytes, indicating they were generated in the oocyte membrane itself, and were not dependent on the presence of enveloping follicular cells. 4. The oscillatory currents reversed around ‐20 mV (the chloride equilibrium potential) and rectified strongly at potentials more negative than about ‐60 mV. The oscillations were mimicked by intraoocyte injection of inositol 1,4,5‐trisphosphate (IP3), were largely preserved after removal of external Ca2+, but were abolished following chelation of intracellular Ca2+ by EGTA. Intraoocyte injection of Co2+ ions failed to generate oscillatory currents. 5. Currents elicited by divalent cations resembled the oocyte's oscillatory responses to acetylcholine and a serum protein. However, the response to divalent cations was not blocked by atropine and furthermore, the relative sensitivities to these agonists varied independently between oocytes from different frogs. 6. We conclude that extracellular Cd2+, Ni2+, Zn2+, Co2+, Mn2+ and Cr2+ interact with the oocyte surface to raise cytosolic levels of inositol phosphates. This causes mobilization of intracellular Ca2+, in turn activating Ca2+‐gated Cl‐ channels in the oocyte membrane. 7. In addition to the large oscillatory currents, divalent cations generated small (5‐50 nA), smooth, maintained currents associated with decreases in membrane conductance. The size and ionic basis of these currents varied between oocytes from different frogs. 8. Zinc ions also elicited smooth currents, associated with an increase in membrane conductance, and carried predominantly by K+. This response was specific to Zn2+ and occurred independently of oscillatory Cl‐ currents. The K+ current was abolished by defolliculation, was potentiated by the cyclic AMP phosphodiesterase inhibitor 3‐isobutyl‐1‐methylxanthine,and showed facilitation with K+ currents generated by the adenylate cyclase activator forskolin.(ABSTRACT TRUNCATED AT 400 WORDS)
Local neuronal circuitry underlying cholinergic rhythmical slow activity in CA3 area of rat hippocampal slices.
Authors: MacVicar B A , Tse F W
Published: December 2014

1. Intracellular and extracellular recordings were obtained from the CA3 area of rat hippocampal slices to study cellular and synaptic mechanisms underlying rhythmic slow activity (RSA). In all impaled CA3 pyramidal neurones, continuous applications of carbachol, a non‐hydrolysable cholinergic agonist, induced first a brief non‐rhythmic excitation and then periodic bursts of RSA which could persist for several hours. Each burst of RSA consisted of 4‐10 Hz oscillatory depolarizations which had a rise time much slower than conventional EPSPs recorded in the same cell. 2. The carbachol‐induced RSA was blocked by atropine; therefore the cholinergic stimulation involved muscarinic receptors. 3. Analyses of simultaneous recordings from pairs of neurones, or a neurone and a glial cell, or a neurone and the extracellular field, indicated that carbachol‐induced RSA was synchronous in a large population of CA3 pyramidal neurones. 4. Complete removal of the dentate gyrus and CA1 region did not block carbachol‐induced RSA in CA3, but applications of tetrodotoxin or inorganic Ca2+ channel blockers (Cd2+, Co2+ or Mn2+) abolished carbachol‐induced RSA. This suggested that the RSA involved propagation of action potentials through a local synaptic network in the CA3 area. 5. Carbachol‐induced RSA was reversibly blocked by a broad‐spectrum excitatory amino acid antagonist (kynurenic acid), but not by two selective N‐methyl‐D‐aspartate (NMDA) antagonists (DL‐2‐amino‐7‐phosphonoheptanoic acid or DL‐2‐amino‐5‐phosphonovaleric acid), a GABAA antagonist (bicuculline), or a GABAB antagonist (phaclofen), suggesting that carbachol‐induced RSA involved primarily non‐NMDA excitatory amino acid, but not GABAergic, synapses. 6. Raising extracellular [Ca2+] beyond 7 mM, which should significantly weaken the polysynaptic recurrent excitation among CA3 pyramidal neurones, abolished carbachol‐induced RSA. This suggests that the recurrent excitation among CA3 pyramidal neurones is necessary for carbachol‐induced RSA in the CA3 area. However, our experiments cannot clarify whether the recurrent excitation, alone, is sufficient for carbachol‐induced RSA.
Interactive effects of isoprenaline, forskolin and acetylcholine on Ca2+ current in frog ventricular myocytes.
Authors: Fischmeister R , Shrier A
Published: December 2014

1. Calcium currents (ICa) were measured in single cells isolated from frog ventricle using the whole‐cell patch‐clamp technique and a perfused pipette. The dose‐dependent stimulatory effects of isoprenaline (Iso, 0.1‐100 microM) and forskolin (Fo. 0.1‐50 microM) on ICa were determined in the presence and absence of acetylcholine (ACh, 10 microM) and/or threshold concentrations of Fo (0.2 microM) and Iso (0.05 microM), respectively. EC50 (i.e. concentration of Iso or Fo at which the response was 50% of the maximum) and Emax (i.e. maximal stimulation of Ica expressed as percentage increase in ICa with respect to control) were measured under each condition. 2. ACh increased EC50 for the stimulatory action of Iso on ICa from 0.84 to 3.72 microM while it reduced Emax from 658 to 185%. Thus, ACh mainly reduced the efficacy of Iso to stimulate ICa. 3. ACh increased EC50 for the stimulatory action of Fo on ICa from 2.06 to 10.26 microM but only slightly reduced Emax from 893 to 778%. Thus, ACh mainly reduced the potency of Fo to stimulate ICa. 4. Intracellular perfusion with 100 microM of hydrolysis‐resistant GTP analogues, GTP‐gamma‐S [guanosine‐5'‐O‐(3‐thiotriphosphate)] and Gpp (NH)p (5'‐guanylylimido‐diphosphate), had no effect on basal ICa but reduced by greater than 50% the stimulatory effect of 2 microM‐Iso on ICa. 5. In the presence of Gpp(NH)p or GTP‐gamma‐S, Fo (3 microM) reversibly increased ICa by 490%, as compared to a 717% increase in control (GTP) intracellular solution. Although ACh could still inhibit Fo‐stimulated ICa, the degree of inhibition was significantly smaller than in the presence of GTP. 6. Extracellular perfusion with low concentrations of a combination of Iso (33 nM) and Fo (330 nM) enhanced ICa to a much greater extent than did either agent alone at 3 times higher concentrations. Thus, low concentrations of Iso and Fo appear to increase ICa in a synergistic fashion. 7. ICa stimulated by a combination of Iso and Fo appeared to be more resistant to inhibition by ACh than when stimulated by either alone. It was the efficacy, rather than the potency, of ACh to inhibit ICa that was reduced upon dual stimulation of ICa. 8. In the presence of 0.2 microM‐Fo, EC50 and Emax for the effects of Iso on ICa were 0.27 microM and 619%, respectively. By comparison with the effects of Iso alone, Fo reduced EC50 approximately 3 times with no significant change in maximal stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Dorsomedial medulla stimulation activates rat supraoptic oxytocin and vasopressin neurones through different pathways.
Authors: Raby W N , Renaud L P
Published: December 2014

1. This study utilized retrograde anatomical tracer techniques and in vivo extracellular electrophysiological studies to examine caudal ventrolateral and dorsomedial medulla afferents to supraoptic nucleus neurosecretory neurones in male Long‐Evans rats. 2. In one series of experiments, pentobarbitone‐anaesthetized animals were subjected to ventral exposure of the hypothalamus and rhodamine‐tagged latex microspheres (0.05‐0.2 microliter) were injected into one supraoptic nucleus. Following perfusion with paraformaldehyde‐glutaraldehyde 18‐24 h later, cell counts were obtained of rhodamine‐ and/or catecholamine‐labelled neurones in the caudal ventrolateral and dorsomedial medulla both ipsi‐ and contralateral to the injection site. 3. In the caudal ventrolateral medulla, each injection labelled fewer than 15% of the catecholaminergic neurones; with small injections, most (68‐100%) of the rhodamine‐labelled neurones also displayed catecholamine histofluorescence. In the caudal nucleus tractus solitarii, one‐half to one‐third as many rhodamine‐labelled cells were observed, but a higher percentage (13‐100%) of these were non‐catecholaminergic. 4. Extracellular recordings were obtained from antidromically identified supraoptic neurones classified as vasopressin (n = 106) or oxytocin (n = 26) secreting. Single cathodal pulses (0.2 ms duration, 0.02‐0.08 mA) applied in the caudal half of the ipsilateral nucleus tractus solitarii evoked a transient (30‐50 ms) activation of 63% of both vasopressin‐ and oxytocin‐secreting neurones. Mean latencies (+/‐ S.E.M.) for vasopressin and oxytocin cells were 49.8 +/‐ 1.0 and 46.5 +/‐ 2.4 ms respectively; these were not significantly different. Similar responses were noted to contralateral stimuli applied to four vasopressin and two oxytocin cells. 5. Vasopressin neurones activated by caudal nucleus tractus solitarii stimulation displayed similar patterns of response to stimulation in the caudal ventrolateral medulla. However, latencies from the nucleus solitarius (mean 47.6 +/‐ 1.4 ms; n = 59) were significantly longer (P less than 0.05) than from the ventrolateral medulla (41.5 +/‐ 2.0 ms; n = 17). In eight out of eleven vasopressin neurones tested, interruption of synaptic transmission through the ventrolateral medulla reduced or abolished the caudal nucleus tractus solitarii‐evoked excitation but had no effect on their response to baroreceptor activation. This manoeuvre affected zero out of five oxytocin cells similarly excited by nucleus solitarius stimulation. 6. These observations indicate that visceral input mediated through the nucleus tractus solitarii is transmitted differentially to supraoptic vasopressin‐ and oxytocin‐secreting neurones.
Activation and desensitization mechanisms of muscarinic current response in single pancreatic acinar cells of rats.
Authors: Maruyama Y
Published: December 2014

1. In single, enzymatically dissociated, rat pancreatic acinar cells both ACh stimulation and IP3 (inositol 1,4,5‐trisphosphate) injection can evoke Ca(+)‐dependent transient current responses. However, exogenously applied IP3 (10 microM) gradually loses its ability to induce the Ca2(+)‐dependent response (an increase in [Ca2+]i) during cell incubation with a saline solution. 2. Administration of IP4 (inositol 1,3,4,5‐tetrakisphosphate, 10 microM) together with the IP3 (the injection of IP3‐IP4 mixture) allows partial recovery of the response, but not full replication of the response induced by ACh (0.2 microM). Injection of IP4 alone never induces the current response. 3. The sensitivity of IP3 recovers after short‐term administration of ACh (0.2 microM), and in turn, the ACh‐induced response is augmented by the presence of internal IP3. These results suggest that a synergism between IP3 and another ACh‐induced substance plays an important role in muscarinic Ca2+ signalling. 4. ACh‐induced responses are inhibited by pre‐incubation (10 min) with an activator of protein kinase C, TPA (12‐O‐tetradecanoylphorbol‐13‐acetate, 16 nM), or augmented by pre‐incubation (10 min) with an inhibitor, H‐7 (1‐(5‐isoquinoline‐sulphonyl)‐2‐methylpiperazine, 10 microM), whilst IP3‐induced responses are unaffected by that with both agents. These results indicate that protein kinase C acts negatively on the signalling elements prior to the formation of IP3. 5. The oscillatory responses, induced by cell dialysis with a nominally Ca2(+)‐free (ca 1‐10 microM) solution containing GTP gamma S (100 microM), are unaffected by the pre‐treatment with TPA or H‐7. In addition, these responses and/or those triggered by short‐term stimulation with ACh and internal GTP gamma S are not influenced by external ACh. On the other hand, the oscillatory responses recorded in acinar cells pre‐treated with H‐7 are tightly controlled by external ACh. 6. Taken together these results suggest that activation of protein kinase C does not affect the activity of GTP‐binding protein, but disconnects the link between the muscarinic ACh receptor and GTP‐binding protein, or inhibits ACh binding to the receptor, in rat pancreatic acinar cells.
Effects of ouabain on potassium transport and cell volume regulation in rat and rabbit liver.
Authors: Farber J L , Holowecky O O , Serroni A , van Rossum G D
Published: December 2014

1. We have examined whether the apparently ouabain‐resistant fraction of cellular volume regulation in liver slices under isosmotic conditions is due to a failure of ouabain to cause complete inhibition of the coupled transport of Na+ and K+. The ion and water contents of rat and rabbit liver slices were altered by pre‐incubation at 1 degree C and then allowed to recover at 38 degrees C, with or without ouabain or other inhibitors. The net movements of ions and water were determined during the recovery. The influx of 86Rb under steady‐state conditions was taken as a measure of unidirectional influx of K+. 2. Concentrations of ouabain for half‐maximal inhibition of 86Rb influx were 0.15 mM for rat and 0.15 microM for rabbit liver slices, with maximal inhibition at 2 mM and 10 microM respectively. Inhibition of net K+ reaccumulation closely followed inhibition of 86Rb influx. 3. The 86Rb influx persisting in the presence of maximally inhibiting concentrations of ouabain was not reduced by inhibitors of cellular respiration or glycolysis. 4. In rat liver slices, about 50% of net water extrusion was resistant to 2 mM‐ouabain; rabbit liver showed a much smaller, but statistically significant, extrusion of water in the presence of 10 microM‐ouabain. 5. In rat liver slices, a small, net uptake of K+ continued in the presence of amytal alone, when water extrusion was completely inhibited; by contrast, ouabain gave complete inhibition of K+ uptake while permitting 50% of the control water extrusion. 6. Isolated rat hepatocytes in primary culture were pre‐incubated at 4 degrees C for 20 h. They recovered their original K+ content within 60 min of restoration to 37 degrees C. Ouabain, 1‐2 mM, completely prevented this recovery. 7. The results imply that ouabain completely inhibits the coupled transport of Na+ and K+ in both rat and rabbit liver slices. Thus, the fraction of total water extrusion continuing in the presence of maximally inhibiting concentrations of ouabain is the consequence of a truly ouabain‐resistant mechanism.
Effects of dehydration and rehydration on thermoregulatory sweating in goats.
Authors: Baker M A
Published: December 2014

1. Measurement of rectal temperature (Tr), sweat rate, respiratory frequency (f) and respiratory evaporation (Eresp) were made in one Nubian and four Alpine‐Toggenberg goats while they stood for 90 min in a climate chamber at 40 degrees C ambient temperature (Ta). The animals were studied when they were hydrated, when they had been dehydrated by 48 h water deprivation, and when they were rehydrated by voluntary drinking of water or saline or by intraruminal water administration. Plasma osmolality (Posm), plasma protein concentration (PP) and haematocrit (Hct) were measured before every experiment and before and after voluntary drinking. 2. Hydrated animals increased evaporation by panting and sweating during heat exposure and Tr rose about 1 degree C. The rate of sweating was as high or higher than Eresp. Dehydrated animals had lower sweat rates and higher Tr than hydrated animals, but f and Eresp were the same in hydrated and dehydrated animals. 3. When dehydrated goats were allowed to drink after 60 min of heat exposure, sweating began abruptly within 3 min of the start of drinking in every animal whether water or saline was drunk. Sweat rate returned to hydrated levels or higher before any change occurred in Posm, PP or Hct. Respiratory frequency was higher after drinking than in dehydrated animals which were not allowed to drink. 4. When water was administered by rumen tube after 60 min of heat exposure, sweating in the Nubian occurred with a short latency, similar to the onset after drinking. In the other four animals, sweating onset occurred on average at 13 min 42 s after intraruminal water administration. 5. It is concluded that sweating is a significant avenue of evaporative heat loss in these goats when they are hydrated and exposed to high Ta. Sweat rate is markedly reduced after water deprivation but returns to hydrated levels within 3 min after the start of drinking. The rapid recovery of sweating after voluntary drinking is not initiated by changes in Posm or in blood volume and does not appear to depend upon osmoreceptors in the mouth or gastrointestinal tract since it occurs after drinking either water or saline. The arrival of water in the rumen may be sufficient to initiate immediate sweating in some goats, but the act of drinking is necessary in others.
Direct evidence of active sympathetic vasodilatation in the skin of the human foot.
Authors: Lundberg J , Norgren L , Ribbe E , Rosén I , Steen S , Thörne J , Wallin B G
Published: December 2014

1. During operative aorto‐femoral vascular reconstructions on sixteen patients, the sympathetic chain was stimulated electrically between the L2 and L4 ganglia while blood flow was monitored by laser doppler flowmeters from the skin on the sole of the foot and the ankle and by an electromagnetic flowmeter from the deep femoral artery. Epidural anaesthesia to at least the T6 level was used which excluded reflex effects. 2. Stimulation (10 Hz) at 1‐12 mA current strengths for 30 s evoked both reductions and increases of blood flow in glabrous and hairy skin. Initial short‐lasting flow increases (durations 9‐19 s) followed by sustained decreases were common: sometimes there were sustained flow increases at low and decreases at high current strengths. 3. In the deep femoral artery (supplying predominantly muscle) only flow reductions were evoked. 4. The results provide evidence for sympathetically mediated vasodilatation in the skin of the human foot whereas leg muscles may be supplied by vasoconstrictor nerves only.
Electrical behaviour of myenteric neurones in the gastric corpus of the guinea‐pig.
Authors: Schemann M , Wood J D
Published: December 2014

1. Electrical behaviour of ganglion cells in the myenteric plexus of the guinea‐pig stomach was investigated using intracellular recording methods. 2. Three subpopulations were identified and classified for convenience of discussion as gastric I, II and III neurones. Gastric I neurones were characterized by repetitive spike discharge during depolarizing current pulses and by higher input resistance than the other types. Gastric II neurones discharged one or two spikes only at the onset of long‐lasting depolarizing current pulses. Gastric III neurones did not discharge spikes to depolarizing current pulses and had higher membrane potentials and lower input resistances than the other types. Non‐stimulus evoked discharge ('spontaneous' discharge) did not occur in any of the neurones. 3. Resting membrane potentials were generated primarily by resting K+ conductance, but were smaller than the estimated K+ equilibrium potential. Analysis based on the constant field equation predicted lower K+ conductance in gastric I than in gastric III neurones. 4. Action potentials in gastric I and II neurones were suppressed or blocked by tetrodotoxin. Spikes that were broadened by tetraethylammonium appeared to have an inward component of Ca2+ current. 5. Hyperpolarizing after‐potentials were associated with the spikes of both kinds of neurones. These after‐potentials had much shorter duration (less than 300 ms) than the post‐spike hyperpolarization of AH/type 2 intestinal neurones and unlike intestinal neurones there was no latency between the positive after‐potential of the spike and the onset of the hyperpolarization. After‐hyperpolarization in the gastric neurones was enhanced when the spikes were broadened by tetraethylammonium and was suppressed by removal of Ca2+ from the bathing solution. 6. Treatment with either tetraethylammonium or 4‐aminopyridine enhanced excitability and induced 'spontaneously' occurring repetitive spike discharge. 7. The electrophysiological behaviour of gastric myenteric neurones differed significantly from intestinal neurones. This was interpreted as specialization of the neural networks that control and co‐ordinate the activity of vastly different effector systems in the two regions of the alimentary canal.
Inhibitory interactions between motoneurone terminals in neonatal rat lumbrical muscle.
Authors: Betz W J , Chua M , Ridge R M
Published: December 2014

1. Evoked synaptic potentials and currents were recorded in neonatal rat fourth deep lumbrical muscle during the period of polyneuronal innervation. Signs of inhibitory interactions between converging mononeurone terminals were detected. 2. Muscle fibres innervated by axons from the lateral plantar nerve (LPN) and from the sural nerve (SN) were studied. In unblocked preparations the muscle contracted, and electrode tips were mounted on flexible wires to prevent loss of impalements. 3. In voltage recordings from unblocked preparations, paired two‐shock stimulation of one nerve revealed synaptic depression: the second response was smaller than the first. When the two stimuli were delivered to different nerves (SN and LPN), the second response was smaller than its own control. 4. In voltage clamped, unblocked preparations, a similar result was obtained. Conditioning stimulation of one nerve (SN, for example) inhibited the response to test stimulation of the other nerve (LPN). The inhibition was greater with larger conditioning responses, was maximal when the conditioning and test stimuli were approximately superimposed, and decayed with a time course of several tens of milliseconds. Several tests showed that the end‐plate was well clamped: the observed inhibition could not be explained by voltage escape at the end‐plate. 5. The inhibition was not constant during the tail of the test end‐plate current (EPC). Instead, it declined during the EPC tail, suggesting that the mechanism of inhibition was active, though diminishing, throughout the time course of the test EPC. 6. The amount of inhibition was not noticeably affected by altering the muscle membrane potential (two cells studied). 7. Treatment with curare or alpha‐bungarotoxin to block most ACh receptors reduced the inhibition. In about half of the fibres studied, no inhibition was evident: in the others, up to 50% inhibition was observed. The average inhibition for all receptor‐blocked fibres was about 15%. 8. In six alpha‐bungarotoxin‐treated cells, multiple conditioning stimuli were delivered. In most cases, the amount of inhibition increased with increasing numbers of conditioning stimuli. 9. Several possible mechanisms of inhibition are discussed, including reduction of current through ACh channels during the test response owing to alterations in synaptic cleft ion concentrations produced by the conditioning response, presynaptic inhibition of transmitter release, and postsynaptic receptor saturation.
GABA and glycine channels in isolated ganglion cells from the goldfish retina.
Authors: Cohen B N , Fain G L , Fain M J
Published: December 2014

1. Adult goldfish retinas were enzymatically dissociated and ganglion cells were maintained in culture for periods of 1‐5 days. Ganglion cells could be identified by their morphology, and this identification was confirmed by retrograde transport of the fluorescent dye Fast Blue injected into the optic nerve stub. 2. All the ganglion cells tested responded to 30 microM‐GABA or 100 microM‐glycine between 2 and 30 h after enzymatic dissociation of the retina. 3. Whole‐cell responses to 30 microM‐GABA or glycine declined over a period of seconds during sustained applications of the agonists, probably as a result of desensitization. There was an irreversible decline in the peak whole‐cell response to repeated applications of 30 microM‐GABA unless the pipette‐filling solution contained 2 mM‐ATP, 4 mM‐Mg2+, 10 mM‐EGTA and no added Ca2+. Both GABA and glycine responses also showed an irreversible decline in outside‐out patches but, in this case, Mg2+, ATP, and very low Ca2+ failed to stabilize the response. 4. Whole‐cell currents activated by both GABA and glycine were demonstrated to be chloride‐selective by investigating the dependence of reversal potential (Vr) on internal chloride concentration ([Cl‐]i). For GABA responses, the dependence of Vr on [Cl‐]i could not be distinguished from that predicted by the Nernst relation. For glycine, deviations from Nernstian dependence were observed, but the permeability to Cl‐ was at least 20 times greater than to isethionate, SO4(2‐), or monovalent cations (Na+ and Cs+). 5. Bicuculline methochloride (10 microM) selectively blocked responses to 3‐30 microM‐GABA without affecting responses to 30 microM‐glycine. Bicuculline itself was not as selective. At agonist concentrations of 30 microM, 3 microM‐bicuculline partially blocked the response to GABA but not that to glycine, but bicuculline at 10 microM blocked responses to both GABA and glycine. Strychnine (0.3‐1 microM) blocked responses to 30 microM‐glycine but also competitively antagonized GABA responses. Picrotoxinin (10 microM) blocked responses to 3 microM‐GABA in some cells but also partially antagonized responses to 30 microM‐glycine. 6. GABA channels had at least two conductance states at 10‐12 degrees C in nearly symmetrical (141 mM in, 142 mM out) chloride. The slope conductance of the most frequently observed (main) state was 16 +/‐ 2 pS. The reversal potential for the main state was not significantly different from the chloride equilibrium potential (0 mV).(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage‐activated currents recorded from rabbit pigmented ciliary body epithelial cells in culture.
Authors: Fain G L , Farahbakhsh N A
Published: December 2014

1. The whole‐cell recording mode of the patch‐clamp technique was used to investigate the presence of voltage‐activated currents in the isolated pigmented cells from the rabbit ciliary body epithelium grown in culture. 2. In Ringer solution with composition similar to that of the rabbit aqueous humour, depolarizing voltage steps activated a transient inward current and a delayed outward current, while hyperpolarization elicited an inwardly rectified current. 3. The depolarization‐activated inward current was mainly carried by Na+ and was blocked by submicromolar concentrations of tetrodotoxin. This current in many cells was sufficiently large to produce a regenerative Na+ spike. 4. The depolarization‐activated outward current was carried by K+ and blocked by external TEA and Ba2+. Its activation appeared to be Ca2(+)‐independent. 5. The hyperpolarization‐activated inward current was almost exclusively carried by K+ and was blocked by Ba2+ and Cs+. For large hyperpolarizations below ‐120 mV, this current exhibited a biphasic activation with a fast transient peak followed by a slower sag, that appeared to be due to K+ depletion. 6. The voltage‐dependent K+ conductances probably act to stabilize the cell membrane resting potential and may also play a role in ion transport. The function of the Na(+)‐dependent inward current is unclear, but it may permit the electrically coupled epithelial cells of the ciliary body to conduct propagated action potentials.
Second messenger‐activated calcium influx in rat peritoneal mast cells.
Authors: Matthews G , Neher E , Penner R
Published: December 2014

1. To study the regulation of calcium influx in non‐excitable cells, membrane currents of rat peritoneal mast cells were recorded using the whole‐cell patch‐clamp technique. At the same time, intracellular calcium concentration ([Ca2+]i) was monitored via the fluorescent calcium‐indicator dye Fura‐2, which was loaded into cells by diffusion from the patch pipette. 2. Stimulation of mast cells with secretagogues, such as compound 48/80 or substance P, caused release of Ca2+ from internal stores. In addition, external agonists also induced influx of external calcium in 26% of the cells investigated. The agonist‐stimulated Ca2+ influx was increased during membrane hyperpolarization and was associated with small whole‐cell currents. 3. Likewise, internal application of inositol 1,4,5‐trisphosphate (Ins1,4,5P3:0.5‐10 microM) elevated [Ca2+]i due both to release of Ca2+ from internal stores and to influx of external calcium. The Ins1,4,5P3‐induced influx was greater at more negative membrane potentials, suggesting that Ins1,4,5P3 opened a pathway through which calcium could enter at a rate governed by its electrochemical driving force. 4. Inositol 1,3,4,5‐tetrakisphosphate (Ins1,3,4,5P4) did not induce Ca2+ influx by itself nor did it facilitate or enhance Ins1,4,5P3‐induced Ca2+ entry. Calcium influx was also induced by inositol 2,4,5‐trisphosphate. Since this inositol phosphate is a poor substrate for Ins1,4,5P3 3‐kinase it seems unlikely that Ins1,3,4,5P4 plays a role in the regulation of the Ca2(+)‐influx pathway in mast cells. 5. The Ins1,4,5P3‐induced Ca2+ influx was associated with whole‐cell currents of 1‐2 pA or less, with no channel activity detectable in whole‐cell recordings. The small size of the whole‐cell current suggests either that the Ins1,4,5P3‐dependent influx occurs via small‐conductance channels that are highly calcium specific or that the influx is not via ion channels. 6. Agonist stimulation also activated large‐conductance (ca 50 pS) cation channels, through which divalent cations could permeate; thus, these channels represent a second pathway for Ca2+ influx. The slow speed of activation of the channels by agonists, their activation by internal guanosine 5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S), and the inhibition of agonist activation by internal guanosine 5'‐O‐(2‐thiodiphosphate) (GDP‐beta‐S) all suggest that the 50 pS channels are regulated by a second messenger and/or a GTP‐binding protein. The activity of the 50 pS channel in mast cells is not sensitive to either Ins1,4,5P3 or Ins1,3,4,5P4. Activity of the channel was inhibited by elevated [Ca2+]i.(ABSTRACT TRUNCATED AT 400 WORDS)
Chloride conductance activated by external agonists and internal messengers in rat peritoneal mast cells.
Authors: Matthews G , Neher E , Penner R
Published: December 2014

1. Stimulation of mast cells by externally applied secretagogues activated a slowly developing membrane current. With high external and low internal chloride (Cl‐) concentrations, the current reversed at about ‐40 mV, but when external Cl‐ was made equal to internal Cl‐, the reversal potential shifted to about 0 mV, demonstrating that the current carrier was Cl‐. 2. In addition to external agonists, internally applied cyclic AMP and high concentrations of intracellular calcium [Ca2+]i could also activate the Cl‐ current. However, elevated [Ca2+]i produced only slow and incomplete activation. This suggests that the Cl‐ current is not directly Ca2+ activated. Also, activation of Cl‐ current by external agonists and by cyclic AMP was unimpaired when [Ca2+]i was clamped to low levels with internal ethylene glycol bis‐N,N,N',N'‐tetraacetic acid (EGTA), indicating that elevated [Ca2+]i is not necessary for activation of the Cl‐ current. Although activation by cyclic AMP was faster than that produced by elevated [Ca2+]i, it still required tens of seconds; thus the effect of cyclic AMP was also likely to be indirect. 3. Internal guanosine 5'‐O‐(3‐thiotriphosphate) (GTP‐gamma‐S) could also activate the Cl‐ current, suggesting the involvement of a G protein in the control of the current. 4. The variance associated with the Cl‐ current was small, and noise analysis gave a lower limit of about 1‐2 pS for the single‐channel conductance. The Cl‐ current was reduced by 4,4'‐diisothiocyano‐2,2'‐stilbenedisulphonate (DIDS), and during DIDS blockade, the variance of the current increased. This suggests that DIDS enters and blocks the open channel. 5. Activation of the Cl‐ current would make the membrane potential negative following stimulation of a mast cell, thus providing a driving force for entry of external calcium via the stimulation‐induced influx pathways described in the preceding paper (Matthews, Neher & Penner, 1989).
The metabolic causes of slow relaxation in fatigued human skeletal muscle.
Authors: Cady E B , Elshove H , Jones D A , Moll A
Published: December 2014

1. The relationship between slowing of relaxation and changes of intracellular pH and phosphorous metabolites has been examined in human skeletal muscle during the development of fatigue and subsequent recovery. Results obtained with normal subjects have been compared with those from a subject with myophosphorylase deficiency (MPD) who produced no H+ from glycolysis during exercise and therefore afforded the opportunity of assessing the role of H+ in the slowing of relaxation. 2. Subjects fatigued the first dorsal interosseous muscle in a stepwise fashion under ischaemic conditions, with intervals between the fatiguing contractions during which the relaxation rate was measured from brief tetanic contractions and the muscle phosphorous metabolites and pH were measured by nuclear magnetic resonance spectroscopy. 3. After 21 s maximal voluntary contraction under ischaemic conditions, relaxation in the MPD subject slowed to approximately 50% of the rate in the fresh muscle at a time when the intramuscular pH had not changed. This demonstrates that there is a mechanism causing slowing of relaxation that is independent of H+ accumulation. 4. The normal subjects showed a slow recovery of relaxation compared to the MPD subject when the circulation was restored. The main difference in the intracellular metabolite concentrations between MPD and normal subjects at this time was that, for the latter, the pH remained low (around 6.5) for at least 60 s after the circulation was restored. The results suggest that the slow recovery is a consequence of continuing acidosis, i.e. the existence of a pH‐dependent mechanism of slowing. 5. The existence of a pH‐dependent mechanism was further indicated by the fact that for the normal subjects, for a similar intracellular concentration of phosphocreatine, relaxation of the recovering muscle was approximately half that of the fatiguing muscle. This was at a time when the pH of the recovering muscle was 0.3‐0.4 units less than in the partially fatigued muscle. 6. The results show that in normal muscle there are at least two processes that lead to slow relaxation in fatigued muscle: one due to H+ accumulation, the other being independent of H+.
Adrenal responses to splanchnic nerve stimulation in conscious calves given naloxone.
Authors: Edwards A V , Jones C T
Published: December 2014

1. The effects of stimulating the peripheral end of the right splanchnic nerve in the presence of naloxone (2 mg kg‐1) have been investigated in conscious 3 to 6‐week‐old calves. 2. Mean aortic blood pressure rose to significantly higher levels during splanchnic stimulation in bursts at 40 Hz for 1 s at 10 s intervals than it did during stimulation at the corresponding continuous frequency (4 Hz). Furthermore, naloxone significantly reduced the fall in mean vascular resistance in response to both patterns of stimulation. 3. The output of catecholamines from the adrenal gland, together with the proportion of noradrenaline released, was significantly enhanced by stimulating the splanchnic nerves in bursts in animals pre‐treated with naloxone and the proportion of noradrenaline released also increased. In both cases the output of adrenaline and noradrenaline was within the same range as that reported previously in normal control animals. 4. Naloxone significantly increased the amounts of enkephalin‐like immunoreactivity and corticotrophin‐releasing factor (CRF)‐like immunoreactivity released from the adrenal gland in response to splanchnic nerve stimulation and raised the proportion of total to free met5‐enkephalin that was secreted. 5. Naloxone also inhibited the rise in plasma adrenocorticotrophic hormone (ACTH) concentration during continuous stimulation at 4 Hz, but not during stimulation at 40 Hz in bursts. Under these latter conditions the output of cortisol apparently directly from the adrenal gland was inhibited. The finding that splanchnic nerve stimulation can potentiate the output of cortisol in response to ACTH was confirmed. 6. These results provide evidence that release of enkephalins and of CRF from the adrenal is inhibited by activating opioid receptors within the gland itself.
Secretory and radioligand binding studies on muscarinic receptors in bovine and feline chromaffin cells.
Authors: Ballesta J J , Borges R , García A G , Hidalgo M J
Published: December 2014

1. Muscarinic agonists enhanced catecholamine release from perfused cat adrenal glands with the following relative order of potencies: methacholine greater than oxotremorine greater than McN‐A‐343 greater than pilocarpine greater than bethanechol greater than muscarine. Because a continuous online electrochemical detection system was used to monitor catecholamine release, this sequence could be obtained at concentrations much lower (1‐10 microM) and during much shorter stimulation times (3‐30 s) than in previous reports. 2. All muscarinic agonists used secreted adrenaline preferentially over noradrenaline. Methacholine evoked a sustained, non‐desensitizing response in the cat adrenal, which declined to basal levels of secretion immediately after Ca2+ removal: upon Ca2+ restoration secretion was restored to the previous plateau. 3. In addition to evoking a direct secretory response, low concentrations of methacholine, pilocarpine, bethanechol or muscarine clearly potentiated cat adrenal secretory responses evoked by pulses of nicotine (2 microM for 30 s) or high K+ (17.7 mM for 30 s). 4. [3H]Quinuclydinyl benzylate (QNB) specifically bound to cat adrenomedullary membranes with a saturating monophasic curve, suggesting a single binding site with a KD of 23 pM and a Bmax of 67 fmol (mg protein)‐1. Preferential displacement by atropine over pirenzepine suggests that the binding site is associated to a M2‐type muscarinoceptor. 5. Methacholine (3‐300 microM) did not enhance the spontaneous catecholamine release from perfused bovine intact adrenal glands or superfused chromaffin cells. Neither did the drug affect secretion evoked by dimethylphenylpiperazinium (10 microM for 3 s) or K+ (35 mM for 3 s) from isolated superfused bovine adrenal chromaffin cells. 6. [3H]QNB bound to purified bovine adrenomedullary plasma membranes with a KD of 29 pM and a Bmax of 89 fmol (mg protein)‐1. Displacement by pirenzepine suggests the presence of two binding sites (Hill coefficient = 0.64) with Ki1 of 39 nM and Ki2 of 2734 nM. 7. Because the ionophore A23187 enhanced K(+)‐evoked secretion in both, bovine and cat adrenals, it seems that a similar cytosolic Ca2+ rise induced by muscarinic stimulation might constitute the underlying mechanism both to cause a secretory response per se as well as the potentiation of catecholamine release evoked by nicotinic or high K+ stimulation. However, it is unclear why the bovine behaves differently from the feline chromaffin cell as far as the muscarine‐evoked effects are concerned.(ABSTRACT TRUNCATED AT 400 WORDS)
Respiratory responses to sustained isometric muscle contractions in man: the effect of muscle mass.
Authors: Imms F J , Mehta D
Published: December 2014

1. Respiratory responses to sustained isometric contractions of a small mass of muscle (the finger flexors) during handgripping, and of a larger mass of muscle (the quadriceps) during extension of the leg at the knee, have been studied in man. 2. For both masses of muscle the increases of ventilation and of oxygen consumption were greater for contractions at 40% maximum voluntary contraction (MVC) than for contractions at 20% MVC. 3. The increase of ventilation was not related to the mass of muscle involved. 4. At 20% MVC oxygen consumption during contraction of the quadriceps was greater than that during handgripping. At 40% MVC the oxygen consumptions were similar. The oxygen debts following both handgrip and knee extensor contractions at 20% MVC were negligible. Following 40% MVC contractions of the quadriceps a significant oxygen debt was recorded but no debt was apparent following 40% MVC contractions of the finger flexors. 5. The increases of ventilation during isometric exercise were generally inappropriately high for the increases of gas exchange. This led to reductions of the end‐tidal carbon dioxide pressure (PET,CO2), especially towards the end of exercise. 6. Following 40% MVC handgripping hyperventilation continued despite the reduced alveolar PCO2. By contrast, following 40% MVC knee extension PET,CO2 transiently rose above the resting level, but did not stimulate ventilation. 7. It appears that following fatiguing isometric contractions hyperventilation continues and appears to be independent of alveolar PCO2. It is suggested that stimuli which increase ventilation during exercise may continue to act during the early phase of recovery.