bluuebunny/crossref_metadata_2025 huggingface dataset:
Amygdaloid influences on brain‐stem neurones in the rabbit.
Authors: Cox G E , Jordan D , Moruzzi P , Schwaber J S , Spyer K M , Turner S A
Published: December 2014

1. Electrical stimulation of the central nucleus of the amygdala in the urethane or alpha‐chloralose anaesthetized rabbit evokes a bradycardia with a rapid onset and a concomitant fall in arterial blood pressure. 2. Extracellular neuronal activity was recorded in the ipsilateral nucleus tractus solitarius and dorsal vagal nucleus whilst stimulating the ipsilateral central nucleus of the amygdala, the aortic and vagus nerves. 3. A total of 213 neurones were activated by stimulation of at least one of these inputs. 93 of these neurones received a marked excitatory input from the central nucleus with a wide range of latencies (2‐100 ms). 50 of these cells also received inputs from either the aortic or vagus nerves, or both. 4. The activity of 42 vagal preganglionic neurones was recorded in the dorsal vagal nucleus of which 22 had properties typical of cardioinhibitory neurones. 9 of these vagal motoneurones received inputs from the central nucleus with latencies between 2 and 100 ms. Of these, 5 had physiological properties indicating they were cardio‐inhibitory neurones. 5. We conclude that neurones in the nucleus tractus solitarius and dorsal vagal nucleus can be influenced by descending inputs arising from the central nucleus of the amygdala. Some of these neurones are also likely to be influenced by afferents innervating the thoracic viscera and arterial baroreceptors. The implications of these observations on the role of forebrain‐brain‐stem interactions in cardiovascular control are discussed.
Changes in elemental concentrations of rat parotid acinar cells following pilocarpine stimulation.
Authors: Izutsu K T , Johnson D E
Published: December 2014

1. Quantitative electron microprobe analysis was used to measure elemental dry weight concentrations in cytoplasm, secretory granules and nuclei of resting and pilocarpine‐stimulated rat parotid gland acinar cells. 2. Secretory granules in resting cells had lower concentrations of Na, Mg, P, Cl and K, and higher concentrations of S and Ca than cytoplasm or nuclei. Nuclei in resting cells had lower S and higher K concentrations than cytoplasm. 3. Three major pilocarpine‐related changes were found: (i) cytoplasmic dry weight concentrations of Na and Ca increased and the concentration of K decreased, (ii) the nuclear concentration of Na increased while that of K decreased and (iii) the concentrations of Na and Cl increased in secretory granules. 4. These results indicate that the nuclear, and cytoplasmic compartments have different mechanisms for regulating their elemental concentrations relative to the secretory granules. 5. The present results are largely consistent with X‐ray microanalysis results from the pilocarpine‐stimulated dog submandibular gland.
Dissociation between force and intracellular sodium activity with strophanthidin in isolated sheep Purkinje fibres.
Authors: Boyett M R , Hart G , Levi A J
Published: December 2014

1. We have recorded membrane potential, intracellular Na activity (aiNa) and force of contraction in sheep Purkinje fibres. Force and aiNa were recorded continuously and simultaneously during exposure to strophanthidin and its subsequent washing off. 2. Exposure to strophanthidin in concentrations of 1.5 X 10(‐7), 5 X 10(‐7) and 10(‐5) M caused an increase in force of contraction which was temporally dissociated from the increase of aiNa. 3. There was hysteresis in the relationship between force and aiNa when the period of increasing force was compared to the period of decreasing force. When force increased on exposure to strophanthidin, the same aiNa was always associated with a higher force than when force was decreasing while washing off the drug. 4. For the same rise of aiNa higher doses of strophanthidin produced larger rises of force than lower doses. 5. When diphenylhydantoin was present in the bathing solution at concentrations of 10(‐5) and 10(‐4) M, the relation between force and aiNa with 10(‐5) M‐strophanthidin had a less steep slope, but still displayed hysteresis. 6. The relationship between force and aiNa during changes of the bathing K concentration also displayed a hysteresis, which was in the same direction as that found with strophanthidin. 7. These results are discussed in relation to proposed mechanisms of action of strophanthidin and more generally in relation to the factors linking force of contraction and aiNa. We conclude that in sheep Purkinje fibres the increase of force caused by strophanthidin is not solely due to an increase of aiNa, and that other interventions can also result in hysteresis between force and aiNa.
A pseudo‐rebreathing technique for assessing the ventilatory response to carbon dioxide in cats.
Authors: Berkenbosch A , DeGoede J , Olievier C N , Schuitmaker J J
Published: December 2014

1. The ventilatory sensitivity to CO2 obtained from a non‐steady‐state step‐ramp CO2 challenge (analogous to the Read rebreathing method) was compared with the one of the steady‐state method. 2. Experiments were performed during normoxia on twenty cats anaesthetized with chloralose‐urethane. In eight of these cats additional measurements were carried out during metabolic acidosis and alkalosis. 3. The slope of the non‐steady‐state ventilatory response curve to CO2 was not significantly different from the steady‐state one only if the ratio of the step‐wise increase in end‐tidal PCO2 (PET,CO2) (A) above its resting value and the subsequent rate of rise of the PET,CO2 (R) was equal to the time constant of the central chemoreflex pathway (tau c). This also held true during metabolic acidosis and alkalosis. 4. It is predicted that in human beings during hyperoxia the ventilatory response line obtained with Read's rebreathing method is to a fair approximation shifted to the right by a value of A with respect to the steady‐state response line, provided A/R = tau c. 5. We argue that Read's prescription that a PET,CO2 equilibrium should be established between mixed venous blood, arterial blood and end‐tidal gas has to be regarded as an experimental condition leading to stable‐experiments rather than dictated by physiological mechanisms.
Lidocaine blockage of basolateral potassium channels in the amphibian urinary bladder.
Authors: Van Driessche W
Published: December 2014

1. Basolateral membranes of the frog urinary bladder were investigated after increasing the cationic conductance of the apical membrane by the incorporation of nystatin. 2. K+ currents were recorded in the presence of a mucosa to serosa oriented K+ gradient (SO4(2‐) Ringer solution). Nystatin caused a rapid rise of the short‐circuit current (Isc) followed by a slow increase over a period of 1‐2 h. 3. Impedance analysis showed that the apical membrane resistance was drastically reduced by nystatin. The slow increase in Isc was accompanied by a progressive increase in basolateral conductance. 4. The transepithelial current and conductance recorded in the presence of nystatin could be depressed with lidocaine added to the mucosal and serosal solution. The effects of lidocaine were completely reversible. 5. Noise analysis showed that lidocaine induced additional fluctuations in Isc. The spectrum of these fluctuations was of the Lorentzian type. This noise component is caused by the random interruption of the current through the basolateral K+ channels. The Lorentzian parameters were used to calculate the microscopic parameters of the basolateral K+ channels.
Ion movements and volume changes induced by catecholamines in erythrocytes of rainbow trout: effect of pH.
Authors: Borgese F , Garcia-Romeu F , Motais R
Published: December 2014

1. Trout red cells suspended in an isotonic medium containing 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. 2. The present investigation demonstrates that the maximum swelling reached by the cells is strongly pH dependent. At pH 7.55 the cells enlarge more rapidly than at pH 7.95 and they reach a maximal volume which is much greater. It is explained by a differential effect of pH on two pathways controlling the movements of cations: K+ loss decreases as pH becomes more acidic in a roughly linear manner. On the contrary Na+ uptake increases as pH becomes more acidic with a maximum around pH 7.30 and then decreases. From this pH dependence it can be expected that the maximum enlargement occurs at about pH 7.30. 3. The complex relationship describing the change in the activity of the Na+‐H+ exchanger as a function of pH (bell‐shaped curve) is explained by the predominant influence of internal H+ on the antiporter in the alkaline range of pH and by the predominant influence of external H+ on the transporter in the acidic range.
Dependence of junctional conductance on proton, calcium and magnesium ions in cardiac paired cells of guinea‐pig.
Authors: Noma A , Tsuboi N
Published: December 2014

1. The dependence of gap junctional conductance on the intracellular concentrations of H+, Ca2+ and Mg2+ was studied in paired myocytes dissociated enzymatically from guinea‐pig ventricle. To apply an internal solution buffered to specific H+, Ca2+ or Mg2+ concentration directly to one aspect of the gap junction, the non‐junctional membrane of one of the pair was mechanically ruptured. The junctional conductance was measured by clamping the membrane potential of the other cell using a two‐pipette voltage‐clamp method. 2. The conductance of the non‐junctional membrane was kept low in comparison with that of the junctional membrane (less than 1/50) by replacing both external and internal K+ with Cs+. 3. The current‐voltage (I‐V) relation of the junctional conductance was linear over the potential range examined (from ‐100 to +100 mV). No voltage or time dependence was detected. 4. The conductance of the gap junction between the paired cells ranged from 90 to 3900 nS with a peak distribution at 1000 nS. 5. The effect of H+ was examined over the pH range 7.4‐5.4, while keeping the free‐Ca2+ concentration at zero, or pCa 6.3 or 7.0 using 2‐10 mM‐EGTA. The junctional conductance was almost constant from pH 7.4 to 6.5 and decreased in a dose‐dependent manner with further acidification. There was no difference in the pH‐conductance relationships at various Ca2+ concentrations. The Hill coefficient was approximately 2.4 and the half‐maximum concentration (pK'H) was 6.1. 6. The closing effect of Ca2+ on the gap junction channel was examined over the concentration range from pCa 7 to 5, while keeping the pH at 7.4, 7.0 or 6.5. At each pH, increasing Ca2+ decreased the junctional conductance with similar Hill coefficients of about 3.4. The pCa‐conductance relationship shifted toward a higher Ca2+ concentration range as the pH was lowered (pK'Ca = 6.6, 6.4 and 5.6, at pH 7.4, 7.0 and 6.5, respectively). 7. Increasing Mg2+ also caused a fall in the junctional conductance over the pMg range 3.0‐2.0 with a pK'Mg of 2.5 (3.2 mM), and a Hill coefficient of 3.0. 8. These results suggest that there are two respective binding sites for divalent cations and H+, and that the gap junctional conductance is regulated reversibly by the ligand‐receptor reactions. Comparing the threshold concentrations of Ca2+ and H+ for electrical uncoupling, it was concluded that Ca2+ plays a more important role in regulating the gap junctional conductance of cardiac cells under physiological conditions.
Ionic and pharmacological properties of reciprocal inhibition in Xenopus embryo motoneurones.
Authors: Soffe S R
Published: December 2014

1. Properties of rhythmic, compound mid‐cycle inhibitory post‐synaptic potentials (i.p.s.p.s), which constitute one of the three main synaptic drives to motoneurones during fictive swimming in Xenopus embryos, have been examined using ionic and pharmacological manipulation. 2. Mid‐cycle i.p.s.p.s are Cl‐ dependent. They are reversed by intracellular Cl‐ injection and attenuated by lowered extracellular Cl‐ concentration. 3. In response to bath application of 100 microM‐glycine or 100 microM‐gamma‐aminobutyric acid (GABA), motoneurones show a decrease in cell input resistance of 24 +/‐ 2.9 M omega (mean +/‐ S.E. of mean) or 16 +/‐ 3.7% and 26 +/‐ 6.0 M omega or 14 +/‐ 2.0% respectively. This is associated with a weak hyperpolarization or depolarization of 0 +/‐ 1.5 mV and ‐3 +/‐ 1.4 mV respectively. Both responses can be made strongly depolarizing by intracellular Cl‐ injection. 4. The response to glycine is blocked by 1 microM‐strychnine but is largely unaffected by bicuculline below 50 microM. The response to GABA is largely blocked by 10 microM‐bicuculline but is unaffected by 1 microM‐strychnine. Both strychnine and bicuculline are therefore specific antagonists in the amphibian embryo preparation. Glycine and GABA are both partially antagonized by 10 microM‐picrotoxin. 5. Mid‐cycle i.p.s.p.s recorded in motoneurones during fictive swimming are reduced in amplitude by 0.5‐1 microM‐strychnine but are largely unaffected by 40 microM‐bicuculline. In embryos immobilized by ventral root transection, 100 microM‐tubocurarine, a likely GABA antagonist in the embryo, has no effect on mid‐cycle inhibition. Glycine is suggested to be the probable transmitter released by commissural interneurones and mediating mid‐cycle inhibition during fictive swimming, acting to increase conductance of Cl‐.
Cardiovascular responses at the onset of exercise with partial neuromuscular blockade in cat and man.
Authors: Iwamoto G A , Mitchell J H , Mizuno M , Secher N H
Published: December 2014

1. In decerebrated cats the cardiovascular, heart rate and blood pressure responses to static muscle contractions were followed from the onset of stimulation of the cut L7‐S1 ventral roots. Heart rate and blood pressure were also followed during maximal voluntary and electrically induced static muscle contractions in man using one leg. In both cat and man contractions were performed under control conditions and tubocurarine‐induced neuromuscular blockade. 2. In the cat, heart rate and blood pressure increased 1.7 s after the onset of the contraction. No cardiovascular responses were seen when the muscle contraction was blocked by tubocurarine. 3. In man, both heart rate and blood pressure increased at the onset of voluntary contractions. Partial curarization reduced strength to 39% of control. The heart rate response was unaffected by tubocurarine while the blood pressure response was reduced from 61 to 32 mmHg. 4. Electrical stimulation of the muscles resulted in 75% of voluntary strength in man. The heart rate response was delayed one R‐R interval in the electrocardiogram but was as large as during voluntary contractions. During partial curarization the heart rate response was significantly smaller and the blood pressure response was reduced from 11 to 8 mmHg. 5. In conclusion, processes in active muscles elicit an increase in heart rate and blood pressure which depends on the intensity of the muscle contraction developed. However, the immediate cardiovascular responses at the onset of voluntary muscle contractions cannot be accounted for by reflexes generated in the working muscles alone.
The receptor‐regulated calcium influx in mouse submandibular acinar cells is sodium dependent: a patch‐clamp study.
Authors: Gallacher D V , Morris A P
Published: December 2014

1. Salivary acini were isolated enzymatically from submandibular glands of adult male mice. The patch‐clamp technique was employed to record K+ currents in cell‐attached patches of basolateral membrane. Application of acetylcholine (10(‐5) M) to the medium bathing the cells results in a pronounced and sustained activation of the K+ channels in the cell‐attached patches, an effect mediated by an intracellular second messenger. In the present study we investigate the mechanism by which acetylcholine achieves activation of K+ channels. 2. The effects of acetylcholine on single‐channel activity were shown to be dependent on extracellular Ca2+, i.e. due to Ca2+ influx. In cells bathed in Ca2+‐free medium acetylcholine activation resulted in no increase in single‐channel open probability. This blockade could be reversed by reintroduction of Ca2+ to the extracellular fluid in the continued presence of the agonist. The effects of acetylcholine in control medium (1.2 mM‐Ca2+) were mimicked by the Ca2+ ionophore, A23187 (10(‐8) M). 3. In K+‐depolarized cells (bathed in a Na+‐free, 145 mM‐KCl solution) there was no evidence of any voltage‐activated Ca2+ influx pathway. In the K+‐depolarized cells acetylcholine application was no longer associated with any increase in the open probability of the K+ channels. K+ channels could be activated by adding A23187 (10(‐8) M) to the high‐K+ solution. 4. Cells bathed in another Na+‐free (N‐methyl‐D‐glucamine substituted for Na+) but non‐depolarizing solution were also refractory to acetylcholine. K+ currents could, however, be activated in patches attached to these cells by application of A23187 (10(‐8) M) or by the introduction of 20 mM‐Na+ to the extracellular fluid in the presence of acetylcholine. The increased activity associated with the reintroduction of Na+ was totally reversed by atropine, i.e. it was receptor regulated. 5. The data presented above indicate that the cholinergic regulation of K+ channels is secondary to the receptor‐regulated activation of a Ca2+ influx pathway. There is no evidence of voltage‐activated Ca2+ influx in these cells. The cholinergic activation of Ca2+ influx is abolished in Na+‐depleted cells. We conclude that the Na+ dependency indicates either that Na+ is involved in the gating of some voltage‐independent Ca2+ channel or that Ca2+ entry is via a coupled Na+‐Ca2+ co‐ or countertransport pathway.
Fluid absorption by rat lung in situ: pathways for sodium entry in the luminal membrane of alveolar epithelium.
Authors: Basset G , Crone C , Saumon G
Published: December 2014

1. The purpose of the investigation was to characterize the luminal membrane and the paracellular pathway of rat lung alveolar epithelium. Experiments were performed on lungs in situ instilled with isotonic, buffered Ringer solution and perfused with blood from a donor rat using cross‐circulation technique. 2. The rate of active Na+ transport was 4.4 pmol/(cm2s). The fluid absorption was 156 nl/s, and was unaffected by the presence of protein in the instillate (166 nl/s). In the absence of Na+, fluid absorption was zero. Amiloride (10(‐3) M) reduced fluid absorption by 60%. Amiloride, combined with absence of D‐glucose, arrested fluid absorption completely. Phloridzin at the luminal side reduced fluid absorption whilst phloretin had no effect. Amiloride together with phloridzin (10(‐3) M) also arrested absorption. Thus, there are two entry systems for Na+ in the luminal membrane: Na+ channels and a Na+‐D‐glucose symport. These results show that alveolar fluid absorption is due to cellular activity. 3. Substitution of Cl‐ with gluconate not only stopped fluid absorption, but led to slight reversal of net fluid movement. 4. Passive unidirectional flux of Na+, determined with 22Na+, was 9.9 pmol/(cm2s) and that of Cl‐, determined with 36Cl‐, was 12.4 pmol/(cm2s). These fluxes were based on an assumed alveolar surface area of 5000 cm2. Transference numbers calculated from these figures are close to those in free solution, suggesting a neutral or weakly charged intercellular junctional pathway. The D‐mannitol permeability in the paracellular pathway was 1.7 X 10(‐8) cm/s. 5. It is a consequence of the proposed mechanism for fluid absorption that it becomes inoperative if the normally high reflexion coefficients for Na+ and Cl‐ are lowered in pathological states. In such conditions pulmonary oedema may develop depending on the net balance of passive mechanical and colloid‐osmotic forces. 6. An explanation of the reversal of fluid transport at the time of birth is presented.
Factors affecting intracellular sodium during repetitive activity in isolated sheep Purkinje fibres.
Authors: Boyett M R , Hart G , Levi A J
Published: December 2014

1. Intracellular Na+ activity (aiNa) was measured using neutral‐carrier Na+‐sensitive micro‐electrodes in voltage‐clamped sheep Purkinje fibres during and after 4 min sequences of depolarizing pulses applied to around 0 mV, at a rate of 2.5 Hz. After trains of pulse duration 50 ms the mean increase in aiNa was 0.65 +/‐ 0.3 mM (mean +/‐ S.D., n = 18) whereas with longer pulse durations this rise became progressively smaller. At pulse durations of 300 ms a fall in aiNa was usually found. 2. Recovery of aiNa after a pulse sequence followed a roughly exponential time course. The half‐time of decline after a rise in aiNa using 50 ms pulses was 111 +/‐ 52 s (n = 10), compared with a half‐time of 318 +/‐ 116 s (n = 6) for recovery from a fall in aiNa during a sequence of 300 ms pulses. 3. Application of 2 mM‐Cs+ to block the pace‐maker current (if) resulted in a decrease in resting aiNa by 0.85 +/‐ 0.45 mM (n = 6) and an outward current shift. Na+ loading during a depolarizing pulse train was greater in 2 mM‐Cs+ than in control solution. The rise in aiNa produced by a train of 50 ms pulses in Cs+ was 1.15 +/‐ 0.4 mM (n = 10). At short pulse durations in the presence of Cs+, Na+ loading at the end of a pulse train increased as a function of pulse duration, becoming maximal at a duration of approximately 50 ms and then diminishing at longer pulse durations. 4. Application of 2.5 X 10(‐5) M‐tetrodotoxin (TTX) produced a fall in resting aiNa of 0.55 +/‐ 0.2 mM (n = 6) and an outward current shift, suggesting that a TTX‐sensitive component of steady‐state Na+ current exists at potentials in the region ‐65 to ‐80 mV. 5. TTX greatly reduced the rise in aiNa during a depolarizing pulse train at all pulse durations tested. A fall in aiNa was now found after trains of shorter pulse duration than in control solution. Similar results were obtained in the absence of TTX if the pulse train was initiated from a holding potential which was positive to the Na+ current (iNa) threshold. When iNa had been blocked, using either TTX or a low holding potential, the mean rise in aiNa after a train of 50 ms pulses was 0.25 +/‐ 0.2 mM (n = 8).(ABSTRACT TRUNCATED AT 400 WORDS)
'Off' tails of intramembrane charge movements in frog skeletal muscle in perchlorate‐containing solutions.
Authors: Huang C L
Published: December 2014

1. Charge movements in response to hyperpolarizing ('off') voltage‐clamp steps were examined in frog skeletal muscle fibres in the presence of 8 mM‐perchlorate. 2. The appearance of prolonged 'off' decays, of duration 50‐100 ms coincided with those of slow 'q gamma' charge transfers in preceding 'on' transients. 3. Charge was conserved in the presence of perchlorate whether testing or pre‐pulse voltages were varied. Additionally, steady‐state charge as a function of voltage was independent of the direction from which the voltage was reached. 4. 'Off' recoveries were most prolonged at voltages around ‐90 to ‐100 mV and became less marked with depolarization. 5. Charging currents in response to hyperpolarizing steps that intercepted prolonged ('q gamma') 'on' decays showed reduced slow 'off' tails but intact 'off' decays at early times. 6. Transients elicited by depolarizing steps that intercepted 'off' tail currents showed decreased slow 'on' components. By varying the time at which 'off' responses were so intercepted, it was shown that 'off' tails can require well over 100 ms to attain a steady state in perchlorate. 7. Prolonged depolarization to a holding potential of ‐30 mV inactivated delayed ('q gamma') components in both 'on' and 'off' responses but left the more rapid ('q beta') decays intact. 8. These observations are easier to reconcile with parallel systems responsible for independent early ('q beta') and delayed ('q gamma') transients in both 'on' and 'off' steps than with the existence of 'q beta' and 'q gamma' transitions in a causal sequence.
Importance of vagal input in maintaining gastric tone in the dog.
Authors: Azpiroz F , Malagelada J R
Published: December 2014

1. Using a gastric barostat to quantify variations in gastric tone, we had previously demonstrated that food ingestion or intestinal nutrient perfusion induces gastric relaxation. These data suggested a basal tonic contraction of the stomach during fasting. 2. To determine the role of vagal input in maintaining fasting gastric tone, we prepared two chronic canine models, either isolating both cervical vagal trunks in a cutaneous tunnel or including the supradiaphragmatic vagi within an implanted cooling jacket. In the fasted conscious dogs, we then studied the effect, on gastric tone, of acute and reversible vagal blockade by cooling. 3. Cervical vagal cooling produced a reversible gastric relaxation and increased the heart rate. Supradiaphragmatic vagal cooling produced a similar gastric relaxation without the cardiac effect. 4. Adrenergic blockade did not change either the base‐line gastric tone or the cooling‐induced relaxation. Adrenaline decreased gastric tone, but vagal cooling still produced a significant relaxation. 5. Atropine alone or combined with adrenergic antagonists produced a gastric relaxation that was not further increased by vagal cooling. Bethanechol increased gastric tone, an effect unchanged by vagal cooling. 6. We conclude that gastric tone during fasting is maintained by a cholinergic input, which is vagally mediated at both the cervical and the supradiaphragmatic levels.
Contractile and electromyographic characteristics of rat plantaris motor unit types during fatigue in situ.
Authors: Gardiner P F , Olha A E
Published: December 2014

1. The ventral root dissection technique was used to obtain contractile and electromyogram (e.m.g.) characteristics of ninety‐five plantaris motor units in situ in pentobarbitone‐anaesthetized rats (n = 20). 2. Motor units demonstrated a wide spectrum of sizes, contractile speeds, and fatigue indices, and were categorized in the same manner as cat hind‐limb motor units. Fast‐fatigable (f.f.) and fast‐intermediate fatigue resistant (f.i.) motor units constituted 20.2 and 25.5% of the motor unit population but together generated over 75% of the cumulative tetanic force. Fast‐fatigue resistant (f.r.) and slow motor units composed 43.6 and 10.6% of the population while producing less than 25% of the aggregate tetanic force. 3. Only f.f. and a portion of f.i. motor units demonstrated extensive e.m.g. amplitude reductions during a standard fatigue test. Mean percentage e.m.g. decrease (from the first spike of the first burst to the last spike of the last burst) was 74.0 +/‐ 27.7% for f.f. units and 28.3 +/‐ 31.0% (mean +/‐ S.D.) for f.i. motor units. Relationships between percentage e.m.g. decline and motor unit size (tetanic force) showed significant (P less than 0.01) positive correlations in f.f. (r = 0.71) and f.i. (r = 0.69) motor units. 4. Backward extrapolation of the time course of the force‐e.m.g. relationship during the fatigue test revealed that declines in e.m.g. may explain 15, 21 and 66% of the force losses in f.r., f.i. and f.f. motor units. Slow motor units were fatigue resistant and demonstrated a mean e.m.g. decline of 4.3 +/‐ 6.2%. 5. Indirectly stimulated whole muscle was more fatigable than a composite constructed from motor unit data because of more severe e.m.g. amplitude reductions in the former. 6. The motor unit mechanical and electrical responses during the fatigue test do not summate linearly during whole muscle contractile activity. This is most likely due to the presence, during whole muscle activity, of metabolic changes during the fatigue regimen which influence neuromuscular propagation of excitation, which are not as severe during single motor unit activity.
Alterations in cytoplasmic calcium sensitivity during porcine coronary artery contractions as detected by aequorin.
Authors: Bradley A B , Morgan K G
Published: December 2014

1. Intracellular‐Ca2+‐force relationships were investigated in porcine epicardial coronary arteries by the simultaneous measurement of aequorin luminescence and isometric force. 2. In response to K+ depolarization and histamine, force and aequorin light rose monophasically. In response to carbachol and serotonin, tonic contractions were accompanied by biphasic aequorin signals consisting of an initial spike followed by a low plateau. Contractions produced by prostaglandin F2 alpha (PGF2 alpha) or the endoperoxide analogue U‐46619 were accompanied by little or no detectable rise in light. 3. Comparison of steady‐state force to steady‐state light levels indicated that agonists gave greater force for a given intracellular Ca2+ concentration ([Ca2+]i) compared to that seen during K+ contractures. 4. In Ca2+‐free bathing media, carbachol produced a transient contraction accompanied by a transient intracellular Ca2+ spike indicating release of Ca2+ from intracellular storage sites. 5. In Ca2+‐free bathing media PGF2 alpha produced a tonic contraction with no detectable change in light. 6. These results suggest that changes in the sensitivity of the contractile apparatus to Ca2+ or other activator systems may be as important a mechanism of contraction as are changes in [Ca2+]i.
Properties of the inspiration‐related activity of sympathetic preganglionic neurones of the cervical trunk in the cat.
Authors: Bachoo M , Polosa C
Published: December 2014

1. The experiments reported here have examined some temporal characteristics of the inspiration‐related sympathetic discharge of the cat in control conditions and during forcing of the respiratory oscillator into marked deviations from its natural frequency. The purpose of these experiments was to establish whether or not the relation of sympathetic to phrenic nerve activity shows properties consistent with the hypothesis that the inspiration‐related sympathetic discharge is driven by a neural oscillator, independent of, but coupled and stably entrained to, the brain‐stem respiratory oscillator. 2. The electrical activity of the whole cervical sympathetic trunk (n = 26) or of small strands of the cervical trunk containing single units (n = 20) and of the phrenic nerve was recorded in pentobarbitone‐anaesthetized, paralysed, artificially ventilated, sino‐aortic denervated cats. Most of the cats were bilaterally vagotomized. 3. The onset of the inspiratory burst of the sympathetic preganglionic neurones had a fixed delay from the onset of the phrenic nerve burst. The level of activity within the burst, in whole cervical trunk recording, reached a maximum in early inspiration and then was maintained at approximately this level for the rest of inspiration (twenty‐two out of twenty‐six cats). In four cats the activity level increased throughout the burst. Individual sympathetic preganglionic neurones displaying inspiration‐related burst firing were characteristically recruited in early inspiration and thereafter maintained an approximately constant firing frequency for the rest of inspiration. 4. Electrical stimulation of afferents in the superior laryngeal nerve during various phases of the respiratory cycle caused equivalent, phase‐dependent, resetting patterns of both phrenic nerve and inspiration‐related sympathetic discharge. 5. In cats with intact vagus nerves, entrainment of the brain‐stem respiratory oscillator to the frequency of the respiratory pump was used to change the frequency of the former, within limits, by changing the frequency of the latter. Over the range of frequencies tested, the pump‐to‐phrenic delay varied as a function of frequency, while the delay between phrenic and sympathetic burst onset was essentially independent of frequency. 6. In hyperthermic, hypocapnic cats phrenic nerve burst frequency increased up to about 300 bursts/min from a value of 15 bursts/min in normothermia‐normocapnia. At all frequencies within this range the sympathetic burst maintained a delay, with respect to the phrenic burst, which was essentially independent of frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Inward current related to contraction in guinea‐pig ventricular myocytes.
Authors: Fedida D , Noble D , Shimoni Y , Spindler A J
Published: December 2014

1. A component of inward current has been identified in isolated guinea‐pig ventricular cells that is closely correlated with the contraction of the cell and not with the rapidly activated calcium current. This is a delayed current most clearly seen as a current 'tail' after 50‐200 ms depolarizing pulses. At 22 degrees C the delayed current has a maximum amplitude of approximately 0.5 nA at ‐40 mV (consistently 10‐20% of the peak amplitude of the calcium current) and decays with a half time of approximately 150 ms. 2. Paired‐pulse protocols show that at pulse intervals (300‐400 ms) at which the calcium current is nearly fully reprimed, the delayed component is very small. It recovers over a time course of several seconds, as does the contraction. Adrenaline speeds the decay of the delayed current (approximately 50%) and similarly accelerates cell relaxation. Adrenaline also shortens the recovery time of both the contraction and the delayed current. 3. During long trains of repetitive pulses, the delayed current amplitude follows that of the contraction 'staircase'. The half‐time of the decay of the current 'tail' also matches that of contraction and suggests that both may reflect the time course of the underlying intracellular calcium transient. 4. The half‐time of decay of the delayed current is only moderately voltage dependent over the potential range ‐80 to 0 mV. The amplitude of the delayed current normally reaches a minimum around ‐20 mV and increases at more negative potentials. 5. The voltage dependence and kinetics of decay of the current show that it should flow and decay largely during the action potential plateau and repolarization rather than during diastole. 6. Diffusion of high concentrations of EGTA into cells abolishes the delayed current and cell contraction. Under these conditions the fast calcium current is increased and its inactivation delayed. 7. When calcium is replaced by strontium, the delayed current amplitude is greatly reduced even though the contraction is larger and slower. 8. The results are consistent with the hypothesis that the delayed inward current is activated by the intracellular calcium transient. It may be carried by the sodium‐calcium exchange process and/or by calcium‐activated non‐specific channels (especially when interal calcium is elevated by reduction of external sodium). 9. In the presence of 1 microM‐ryanodine, the calcium current is greatly reduced, whereas the delayed current is not significantly altered.
Two distinct calcium‐activated potassium currents in a rat anterior pituitary cell line.
Authors: Ritchie A K
Published: December 2014

1. The single ‘giga‐seal’ patch‐electrode technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was used to record whole‐cell currents in the GH3 rat anterior pituitary cell line. 2. GH3 cells have a rapidly inactivating, voltage‐dependent K+ current that is selectively inhibited by 4‐aminopyridine (4‐AP) but not by tetraethylammonium chloride (TEA). 3. The majority of the Ca2+‐activated K+ current in these cells is blocked by TEA with an inhibitory concentration that is half‐maximal at 1 mM. An additional Ca2+‐activated K+ current is also present that is relatively resistant to TEA and is blocked by the polypeptide apamin. The apamin‐sensitive component represents less than 18% of the total Ca2+‐activated K+ current at 0 mV. 4. The time course of the slowly declining components of the Ca2+‐activated K+ tail currents measured at the ‐50 mV holding potential was usually biexponential with time constants of 0.21 +/‐ 0.02 and 1.75 +/‐ 0.23 s (mean +/‐ S.E. of mean, n = 14). Both of the two slowly decaying components contribute to the TEA‐ and apamin‐sensitive currents. 5. It is concluded that GH3 cells have at least two pharmacologically distinct Ca2+‐activated K+ currents and a 4‐AP‐sensitive voltage‐dependent K+ current.
Thyrotropin‐releasing hormone stimulates a calcium‐activated potassium current in a rat anterior pituitary cell line.
Authors: Ritchie A K
Published: December 2014

1. The ‘giga‐seal’ patch‐electrode technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was used for constant current and voltage‐clamp recordings in the GH3 rat anterior pituitary cell line. 2. Thyrotropin‐releasing hormone (TRH) causes a membrane hyperpolarization that is mediated by a selective increase in K+ permeability. The hyperpolarization cannot be evoked when the cell is internally perfused with a Ca2+ chelator but persists when the external solution that bathes the cell is Ca2+‐free or contains a Ca2+‐channel blocker. 3. Under voltage clamp the TRH‐induced current is approximately linear at negative potentials (‐90 to ‐30 mV) but markedly enhanced at voltages above ‐30 mV). Thus, the affected conductance has a voltage‐dependent component. 4. The TRH‐induced increase in K+ permeability is sensitive to inhibition by 30 mM‐TEA and 200 nM‐apamin, inhibitors of two distinct Ca2+‐activated K+ permeabilities in GH3 cells. 5. The time course of the TRH‐induced K+ current is similar to the time course of a TRH‐induced transient peak elevation of cytosolic Ca2+ that is due to mobilization of Ca2+ from intracellular stores. 6. The effects of TRH on the K+ current and the rise in cytosolic Ca2+ are half‐maximal at 7 nM and 1.7 nM, respectively. 7. It is concluded that the TRH‐induced hyperpolarization is mediated by two distinct Ca2+‐activated K+ conductances that are activated by release of Ca2+ from an intracellular site.
Effects of the calcium antagonist gallopamil (D600) upon excitation‐contraction coupling in toe muscle fibres of the frog.
Authors: Berwe D , Gottschalk G , Lüttgau H C
Published: December 2014

1. The effects of the Ca2+ antagonist gallopamil (D600) upon force development in short skeletal muscle fibres (m. lumbricalis digiti IV) of the frog were investigated under voltage‐clamp control, using two flexible internal micro‐electrodes (temperature = 6‐7 degrees C). 2. In the presence of 5‐100 microM‐gallopamil muscle fibres developed one normal phasic contracture when they were depolarized from a holding potential of ‐90 to 0 mV. Subsequent depolarizations caused no mechanical response (paralysis). However, the ability to contract could be restored by hyperpolarizing the membrane to potentials between ‐120 and ‐150 mV. 3. In the absence of gallopamil, mechanical refractoriness could be fully reversed within 5‐7 s by repolarizing the fibre from 0 to ‐120 mV. In the presence of 100 microM‐gallopamil, no detectable restoration occurred within the first minute at ‐120 mV, and 45 to 100% of maximum force was eventually reached after 6 min of restoration. 4. The potential V at which the 'steady state' 50% of maximum force of a refractory fibre was restored shifted from ‐51 mV under normal conditions to ‐83 and ‐90 mV in the presence of 5 and 100 microM‐gallopamil, respectively. 5. Paralysis in the presence of gallopamil and recovery from paralysis during hyperpolarization could also be observed when 2 mM‐Cd2+ was applied to the external solution, i.e. when most Ca2+ channels in the T‐tubular system were blocked. 6. Gallopamil shifted the threshold for activation of force to more negative potentials. Fibres developed force when they were depolarized to membrane potentials between ‐60 and ‐80 mV, whereby a fast phase of activation was followed by a slower one. Upon repolarization relaxation likewise occurred in a fast and a slow phase. 7. High concentrations of gallopamil (greater than 500 microM) caused a slowly developing contracture, independent of membrane potential (‐90 or 0 mV). 8. It is proposed that gallopamil binds to a receptor at the force‐controlling system in the T‐tubular membrane (potential sensor) with a high affinity in the depolarized state and a lower affinity at negative potentials. Therefore association of gallopamil mainly leads to stabilization of the inactive state (paralysis) but can also stabilize the active state.
Calcium channel currents and their inhibition by (‐)‐baclofen in rat sensory neurones: modulation by guanine nucleotides.
Authors: Dolphin A C , Scott R H
Published: December 2014

1. The effect of intracellular application of the hydrolysis‐resistant GTP and GDP analogues, guanosine 5'‐O‐3‐thiotriphosphate (GTP‐gamma‐S), and guanosine 5'‐O‐2‐thiodiphosphate (GDP‐beta‐S) has been examined on voltage‐activated calcium‐channel currents and the ability of the gamma‐aminobutyric acid B agonist baclofen to inhibit them, in cultured rat dorsal root ganglion (d.r.g.) neurones. 2. Under control conditions, the calcium‐channel current, recorded using the whole‐cell patch technique with Ba2+ rather than Ca2+ as the permeant divalent cation, consists of an inactivating and a sustained current. In the presence of 500 microM‐GTP‐gamma‐S included in the patch pipette, the calcium‐channel current was activated more slowly and was largely non‐inactivating during the 100 ms depolarization voltage step. The effects of GTP‐gamma‐S were abolished by pre‐treatment of cells with pertussis toxin. 3. The calcium‐channel current recorded in the presence of 500 microM‐GDP‐beta‐S had a more marked transient component than the control calcium‐channel current. The proportion of transient calcium‐channel current in the presence of GDP‐beta‐S was not reduced in Na+‐free medium. 4. No statistically significant effects of GTP‐gamma‐S and GDP‐beta‐S were observed on the calcium‐activated potassium current IK(Ca), the transient outward potassium current activated in Ca2+‐free medium, or on the inwardly rectifying current (Ih) activated by hyperpolarization. 5. GTP‐gamma‐S increased the ability of baclofen to inhibit calcium‐channel currents, whereas this was decreased by GDP‐beta‐S and by pre‐treatment of cells with pertussis toxin. The half‐maximal effective dose (EC50) for baclofen was 2 microM in the presence of GTP‐gamma‐S, 15 microM for control and 50 microM in the presence of GDP‐beta‐S. Comparable results were obtained using a single concentration of the adenosine agonist 2‐chloroadenosine (2‐CA, 0.05 microM) to inhibit calcium‐channel currents; its effect was significantly increased by GTP‐gamma‐S and reduced by GDP‐beta‐S. 6. The ability of baclofen to inhibit calcium‐channel currents was not affected by 1 microM‐forskolin or 50 microM‐intracellular cyclic AMP. 7. It is concluded that calcium channels in d.r.g.s are associated with a nucleotide binding protein, and that this mediates the effect of baclofen and 2‐CA on calcium‐channel currents. The ability of GTP‐gamma‐S to inhibit the transient component of calcium‐channel currents in the absence of agonist may represent a means of differentially regulating calcium‐channel activity.
Are ninhydrin‐positive substances volume‐regulatory osmolytes in rat renal papillary cells?
Authors: Law R O , Turner D P
Published: December 2014

1. A study has been made of the concentrations and contents of ninhydrin‐positive substances (n.p.s.), presumed to be predominantly but not exclusively amino acids, in the cells of rat renal papillary slices incubated in variously modified Krebs phosphate‐bicarbonate Ringer solution. 2. When the medium osmolality was increased from 710 (control) to 2000 mosmol/kg H2O by additional NaCl and urea, the steady‐state cellular n.p.s. concentration rose from 42.3 +/‐ 0.6 (mean +/‐ S.E. of mean; n = 36) to 105 +/‐ 2 (n = 68) mmol/l (glycine equivalent). Cell fluid content fell from 5.11 +/‐ 0.09 (n = 36) to 4.16 +/‐ 0.11 (n = 68) microliter/mg solute‐free dry weight. Hence cell n.p.s. content increased from 211 +/‐ 4 (n = 36) to 421 +/‐ 10 (n = 68) nmol/mg solute‐free dry weight. 3. A comparable loss of cell fluid was observed when urea was replaced by sucrose or sorbitol. No increase in cell n.p.s. occurred, and there was a marked cell Na+‐for‐K+ exchange. 4. The extent of the increase in cell n.p.s. in the presence of 2000 mosmol/kg H2O (NaCl + urea) was sensitive to the presence of external anions in the sequence acetate less than Cl‐ less than NO3‐ less than or equal to SCN‐. 5. Cell n.p.s. concentration increased progressively as the medium osmolality was increased by the addition of urea, but Na+ at a concentration above 330 mmol/l had an inhibitory effect. The increase in n.p.s. concentration was also significantly reduced in hyperosmotic media in which Na+ was replaced by choline. 6. The increase in cell n.p.s. content due to hyperosmotic NaCl + urea was completely inhibited by pre‐incubation in control medium containing trimethylamine N‐oxide. 7. On transference of slices from control to hyperosmotic media (NaCl + urea) the steady‐state increase in cell n.p.s. concentration was complete within 20 min and followed a time course similar to that for cell fluid loss. The n.p.s. concentration and cell fluid content returned to control levels, with similar time courses, following re‐immersion in control medium. 8. Efflux of alpha‐amino[1‐14C]isobutyric acid (AIB) from slices pre‐loaded in control medium containing 1 mmol AIB/l was slightly but significantly slower into AIB‐free hyperosmotic NaCl + urea than into AIB‐free control medium. The rate of efflux was greatly increased by the presence of hyperosmotic sucrose or very high Na+ (935 mmol/l).(ABSTRACT TRUNCATED AT 400 WORDS)
Gradual and stepwise changes in the membrane capacitance of rat peritoneal mast cells.
Authors: Almers W , Neher E
Published: December 2014

1. The membrane capacitance of mast cells was monitored under voltage clamp, using sinusoidal excitation and a lock‐in amplifier. 2. Degranulation was accompanied by stepwise capacitance increases that presumably represent the fusion of single secretory granules with the cell membrane. Besides capacitance steps, we also observed gradual changes in capacitance that occurred even in the absence of degranulation, were independent of the presence of nucleotides in the pipette, and were steeply dependent on cytoplasmic [Ca2+]. 3. Cytoplasmic Ca2+ at concentrations of 0.3‐3 microM stimulated a decline in capacitance, with a dose‐response curve suggesting control by the binding of Ca2+ to high‐affinity intracellular sites. When maximally activated, this mechanism could lead to a loss of about 6% of the cell membrane capacitance, at an average rate of 0.1‐0.2% s‐1. 4. At even higher cytoplasmic [Ca2+] (greater than 3 microM), the reverse effect was observed. The capacitance increased gradually by up to 40%, at an average rate of 0.4% s‐1. Evidently gradual changes in membrane capacitance can occur by two mechanisms, and both are influenced by cytoplasmic [Ca2+]. 5. Ca2+ frequently stimulated an inward current accompanied by an increase in membrane conductance. 6. The effects described above were observed also when only trace amounts of Ca2+ and chelator were added to the cytosol, and when increases in cytosolic [Ca2+] could have occurred only by endogenous mechanisms. It is suggested that these effects occur also in intact cells during the large [Ca2+] increases known to occur before and during degranulation.