bluuebunny/crossref_metadata_2025 huggingface dataset:
Central and peripheral effects of the peptide ANF on renal function and blood pressure in hypertensive rats.
Authors: al‐Barazanji K , Balment R J
Published: December 2014

1. The present study assesses renal and blood pressure effects of systemically and intracerebroventricularly (I.C.V.) administered atrial natriuretic factor (ANF) in anaesthetized New Zealand genetically hypertensive (NZGH) rats and their normotensive substrain (NZN). 2. Plasma ANF concentration was significantly raised in NZGH compared with NZN animals. Intravenous ANF administration increased circulating ANF concentration to similar levels in NZGH and NZN rats. Plasma aldosterone concentrations were initially similar in normotensive and hypertensive animals and were reduced markedly by I.V. ANF administration in both groups. 3. Peripheral administration of ANF produced a significant and sustained hypotension during the period of the hormone administration in NZGH animals, while arterial mean blood pressure (MBP) was not altered significantly in NZN rats. Central infusion of ANF produced no change in MBP in either NZGH or NZN animals. There was no detectable change in heart rate during central or peripheral administration of the hormone in either group. 4. By comparison with animals maintained on hormone‐free infusate, urine flow changed little over the 80 min period of I.V. ANF infusion in NZGH rats but was markedly increased in NZN animals. Urinary sodium excretion was elevated during ANF infusion in both NZGH and NZN animals. Central infusion of ANF produced a diuresis in NZN rats but a slight reduction in urine flow in NZGH animals, while sodium excretion was not affected in either group. 5. It appears from the present study that central and peripheral ANF effects on renal function and blood pressure differ in hypertensive and normotensive animals. These differences may in part reflect adjustments to long‐term elevation in plasma ANF in hypertension and in part are possibly associated with disturbances in related endocrine mechanisms.
Autonomic nervous control of nasal vasculature and airflow resistance in the anaesthetized dog.
Authors: Lung M A , Wang J C
Published: December 2014

1. In pentobarbitone‐anaesthetized dogs with constant‐flow vascular perfusion of nasal mucosa on both sides, nasal airway resistance, vascular resistance, vascular capacitance (via changes in total venous outflow) and blood flow in the anterior and posterior venous systems were measured. 2. Electrical stimulation of the cut peripheral ends of the cervical sympathetic trunk, caudal nasal nerve, or major palatine nerve increased vascular resistance and decreased vascular capacitance and airway resistance. Propranolol and atropine had no effect on the responses while bretylium completely abolished them; phentolamine greatly lessened the vascular resistance response and partially decreased the vascular capacitance and airway responses. Hence, sympathetic stimulation causes constriction of the resistance vessels via alpha‐adrenergic mechanism and constriction of capacitance vessels via alpha‐adrenergic as well as some non‐adrenergic and non‐cholinergic mechanisms. 3. Denervation of the cervical sympathetic trunk, caudal nasal nerve and major palatine nerve decreased nasal vascular resistance and increased vascular capacitance and airway resistance, suggesting tonic sympathetic discharge to nasal mucosa via caudal nasal and major palatine nerves. 4. Electrical stimulation of the nerve of pterygoid canal decreased vascular resistance but increased vascular capacitance (in the posterior venous system) and airway resistance to low‐voltage stimulation (below 10 V), and decreased vascular capacitance (in the anterior venous system) and airway resistance to high‐voltage stimulation (above 10 V). Hexamethonium reversed the vascular resistance response as well as vascular capacitance and airway responses to high‐voltage stimulation. Bretylium and phentolamine enhanced the vascular resistance response and reversed vascular capacitance and airway resistance responses to high‐voltage stimulation. Hence, low‐voltage stimulation results in parasympathetic dilatation of resistance and capacitance vessels whereas high‐voltage stimulation results in parasympathetic dilatation of resistance vessels and sympathetic constriction of capacitance vessels. The parasympathetic vasodilatation was atropine resistance and the sympathetic vasoconstriction was partially via alpha‐adrenergic mechanisms. 5. Denervation of the nerve of pterygoid canal did not affect vascular resistance, vascular capacitance or airway resistance suggesting negligible tonic parasympathetic and sympathetic discharges to nasal blood vessels via the nerve. 6. Simultaneous optimal stimulation of sympathetic and parasympathetic nerves resulted in vasoconstriction, especially in capacitance vessels, suggesting sympathetic predominance over parasympathetic control.
Chloride and bicarbonate transport in fetal red cells.
Authors: Brahm J , Wimberley P D
Published: December 2014

1. Chloride (JCl) and bicarbonate (JHCO3) self‐exchange flux in fetal human red cells was studied at 0‐38 degrees C as 36Cl‐ and [14C]HCO3‐ efflux. 2. Both at 0 and 38 degrees C JCl showed a bell‐shaped pH dependence with a broad maximum at pH 7‐8. JCl was 99.7% inhibited by the binding of 1.1 x 10(6) 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonate (DIDS) molecules per cell membrane. 3. By raising the temperature from 0 to 38 degrees C JCl, at external concentration (C0) = 150 mM, increased about 200 times to 5 x 10(‐8) mol/(cm2 s), the half‐time of the tracer efflux being 80 ms at 38 degrees C and pH 7.2. Under conditions where Co = (110 mM‐Cl‐ + 25 mM‐HCO3‐), JCl also increased by about 200 times, while JHCO3 increased only about 100 times, as temperature was raised from 0 to 38 degrees C. 4. The apparent activation energy (EA) of Janion was not constant, but increased gradually with decreasing temperature. Assuming that the change of EA with temperature consists of two components JCl, under both experimental conditions, had average values of EA = 117‐120 under and EA = 73‐78 kJ/mol above a ‘breaking’ point at 15‐20 degrees C, while JHCO3 showed an EA = 100 below and EA = 48 kJ/mol above 25 degrees C. 5. We conclude that the anion transport protein becomes built into the membrane at a very early stage of life, and that the kinetics of Janion in fetal red cells show characteristics that are similar to those of adult red cells. 6. Our results suggest that the CO2 transport capacity of the fetal blood can be exploited during rest nearly as efficiently as that of adult blood.
Effects of age on calcium transport activity of sarcoplasmic reticulum in fast‐ and slow‐twitch rat muscle fibres.
Authors: Larsson L , Salviati G
Published: December 2014

1. The calcium transport activity of the sarcoplasmic reticulum (SR) was measured in chemically skinned single fast‐ and slow‐twitch muscle fibres from young (3 months) and old (23‐24 months) rats. Contractile properties, the myosin heavy chain (MHC) composition and enzyme histochemical features were studied in relation to the SR characteristics. 2. In fast‐twitch single motor units, the contraction time of the isometric twitch increased (P less than 0.001) from 13 +/‐ 1 ms in young animals to 18 +/‐ 2 ms in old ones. In the slow‐twitch soleus, the contraction (P less than 0.001) and half‐relaxation (P less than 0.05) times increased from 30 +/‐ 5 and 45 +/‐ 10 ms, respectively, in the young animals to 43 +/‐ 3 and 55 +/‐ 4 ms in the old ones. The proportion of slow‐twitch (type I) fibres increased (P less than 0.05) with age in the soleus from 92 +/‐ 6 to 98 +/‐ 2% and the proportion of fast‐twitch fibres (type IIA) decreased (P less than 0.01) from 6 +/‐ 5 to 0 +/‐ 0%. 3. The Ca2+ accumulation capacity (an index of SR volume), the rate of Ca2+ uptake and the fractional rate of SR filling (an estimate of the specific activity of the Ca2+ pump) were decreased by 18 (P less than 0.05), 32 (P less than 0.01) and 32% (P less than 0.001), respectively, in the old fast‐twitch muscle fibres. In the slow‐twitch muscle fibres, on the other hand, no significant age‐related changes were observed in the Ca2+ transport activity of the SR. Thus, ageing exerts a differential influence on SR volume and function in fast‐ and slow‐twitch fibres. 4. It is concluded that an age‐related impairment of intrinsic SR function and a decrease in SR volume are probable factors underlying the decreased speed of contraction of fast‐twitch muscle fibres in old age. In the slow‐twitch soleus, on the other hand, one or more other mechanisms are responsible for the age‐related decrease in the speed of contraction. The loss of fast‐twitch muscle fibres in old soleus is one mechanism, but not the dominant one.
Bradykinin‐evoked changes in cytosolic calcium and membrane currents in cultured bovine pulmonary artery endothelial cells.
Authors: Cannell M B , Sage S O
Published: December 2014

1. Cultured bovine pulmonary artery endothelial cells were voltage clamped using a single microelectrode while cytosolic free calcium concentration ([Ca2+]i) was simultaneously measured using the fluorescent calcium indicator, Indo‐1. 2. The resting current‐voltage relationship was non‐linear and exhibited marked inward rectification near the resting potential. In about 60% of cells examined, superfusion of saline resulted in a hyperpolarization and decrease in inward current. This result did not depend on the presence of agonist and is consistent with the presence of extracellular potassium accumulation in restricted spaces around the cell and the known dependence of the inward rectifier. In other cells there was no effect. 3. Resting [Ca2+]i was sensitive to membrane potential, decreasing continuously with membrane depolarization over the range ‐70 to +60 mV. This result is consistent with a simple pump‐leak model and suggests that voltage‐dependent calcium channels are not present in these cells. 4. Bradykinin (10 microM) increased [Ca2+]i after a delay of approximately 3 s. [Ca2+]i reached a peak after a further 3 s and declined over several minutes. 5. During the rise in [Ca2+]i evoked by application of bradykinin, there were no changes in the current‐voltage relationship of the cell. These results question the role of a receptor‐operated non‐selective cation channel in mediating the increase in [Ca2+]i. This observation, coupled with the observed delay in the agonist‐evoked response suggests that a second messenger system is involved in mediating the increase in [Ca2+]i. 6. Changes in the current‐voltage relation started to occur about 30 s after the application of agonist. These changes could be explained by the activation of large‐conductance potassium and non‐selective cation channels with a reversal potential near 0 mV. The latter channels may mediate the plateau phase of the agonist‐evoked response. 7. The results are discussed with respect to the pathways for calcium entry into the cell and possible explanations for discrepancies between the results of this and other studies are presented.
Dynamic response of the coronary circulation to a rapid change in its perfusion in the anaesthetized goat.
Authors: Dankelman J , Spaan J A , Van der Ploeg C P , Vergroesen I
Published: December 2014

1. We tested predictions of a mathematical formulation of a hypothesis of dynamic control of coronary blood flow by tissue oxygen tension. 2. The rate of change of adjustment of the coronary circulation to a step change in arterial perfusion was analysed in the cannulated main stem preparation of the anaesthetized goat. The variable studied was the ratio between driving pressure and coronary flow, each averaged per heart beat. The response of this ratio was measured following a sudden change in perfusion pressure with constant‐pressure perfusion and a sudden change in flow with constant‐flow perfusion. 3. The rate of change of the pressure‐flow ratio was quantified by t50, the time required to establish half of the completed response. For a pressure decrease t50 was 4.9 +/‐ 0.2 s (n = 35) (mean +/‐ S.E.M., n = number of individual measurements), 11.3 +/‐ 1.2 s (n = 25) for a flow decrease, 14.5 +/‐ 1.6 (n = 34) for a pressure increase and 25.1 +/‐ 2.3 (n = 19) for a flow increase. 4. No effect of the level of flow or pressure on t50 was found for a decrease in perfusion. Furthermore, with a flow increase, the t50 value did not depend on the level of flow, which is in agreement with the outcome of earlier experiments where the response to a change in heart rate was measured. With a pressure increase, the mean t50 value of the pressure‐flow ratio was lower at high perfusion pressure but the difference with low perfusion pressure was not significant (P = 0.11). 5. The t50 value in the cases of an increase in pressure and flow are similar to those found for a change of heart rate in an earlier study. 6. Unlike step changes of metabolic rate, some of the measured responses to mechanical step changes were not predicted by the oxygen hypothesis. It is suggested that the increased rate of coronary adjustment induced by the reduction of coronary perfusion is due to arteriolar smooth muscle mechanics which apparently differ in strength depending on the direction of change of the arteriolar dimensions. 7. This suggestion is strengthened by the results of experiments in which smooth muscle responses were abolished with adenosine.
Voltage‐gated and chemically gated ionic channels in the cultured cochlear ganglion neurone of the chick.
Authors: Yamaguchi K , Ohmori H
Published: December 2014

1. Electrophysiological properties of ionic channels of isolated or cultured cochlear ganglion (CG) neurones from chick embryo were studied under voltage‐clamp conditions using a patch electrode. 2. Tetrodotoxin‐sensitive Na+ current was activated by a step depolarization more positive than ‐40 mV, and was inactivated rapidly. 3. Outward‐going K+ current was activated by step depolarization to membrane potentials more positive than ‐62 mV. 4. Two types of Ca2+ currents were demonstrated, an inactivating and a non‐inactivating type. The inactivating type was activated by step depolarizations more positive than ‐69 mV and was inactivated rapidly. The non‐inactivating type was activated by step depolarizations more positive than ‐52 or ‐41 mV depending on the external divalent cation species. 5. The I‐V relationship and the activation kinetics of the non‐inactivating type Ca2+ channel was shifted in a positive direction along the voltage axis by 12 mV when extracellular 2.5 mM‐Sr2+ or Ba2+ were replaced by Ca2+. This shift was not observed in the inactivating type Ca2+ channel. 6. The amplitude of peak current through the inactivating type Ca2+ channel was in the order of Ca2+ greater than Sr2+ greater than Ba2+. The order of relative permeability through the non‐inactivating type estimated from the tail current amplitude was Ba2+ greater than Sr2+ greater than Ca2+. 7. After 5 days in culture, glutamate (30 microM), aspartate (100 microM), kainate (100 microM) and N‐methyl‐D‐aspartic acid (NMDA; 100 microM) elicited ionic currents. The glutamate response was depressed by 1 mM‐Mg2+ in a voltage‐dependent manner at negative membrane potentials and was almost extinguished by amino‐phosphonovalerate (APV) (0.1 mM). The major subtype of glutamate receptor could be of the NMDA type. 8. The permeability of the NMDA receptor channel to Na+ and Li+ was estimated from the reversal potential and was 1.0 and 0.7 compared with that of Cs+, respectively. 9. Divalent cations were more permeable than the monovalent cations through the NMDA receptor channel: PCa greater than or equal to PBa greater than PSr greater than PCs.
Effect of Na+ and K+ on Cl‐ distribution in guinea‐pig vas deferens smooth muscle: evidence for Na+, K+, Cl‐ co‐transport.
Authors: Aickin C C , Brading A F
Published: December 2014

1. Smooth muscle cells of the guinea‐pig vas deferens after Cl‐ depletion actively reaccumulate ions to a level many times higher than that predicted by a passive distribution, even when anion exchange (largely responsible for Cl‐ movements in this preparation) is inhibited by DIDS (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid). The cells therefore must possess a second mechanism for Cl‐ accumulation. We have now investigated the ionic requirement of this mechanism using a combination of ion analysis, 36Cl fluxes and direct measurement of the intracellular Cl‐ activity (aiCl). 2. In the steady state, the Cl‐ content of tissues was 12‐16% less in Na(+)‐free solution than in normal Krebs solution. 3. Loss of 36Cl into Cl(‐)‐free solution was slowed by the absence of Na+ and accelerated on its readdition. Uptake of 36Cl by Cl(‐)‐depleted tissues was also reduced in the absence of extracellular Na+, particularly at longer time intervals as uptake reached completion. These effects occurred in the presence and absence of CO2‐HCO3‐ and in the presence of DIDS. 4. The initial rate of rise of aiCl on readdition of Cl‐ to Cl(‐)‐depleted cells was not significantly affected by the absence of Na+ in the presence of a functional anion exchange, but aiCl stabilized at a lower value than in normal solution. Readdition of Na+ stimulated a rise in aiCl to the control level. Removal and readdition of K+ under these conditions had negligible effects. 5. When anion exchange was inhibited by the presence of DIDS, removal and readdition of Na+ caused, respectively, a marked inhibition and stimulation of the rise in aiCl during Cl‐ reaccumulation. Under these conditions removal and readdition of K+ had similar effects. 6. The results suggest that Na+, K+, Cl‐ co‐transport is involved in transmembrane movements of Cl‐ at least when the anion exchange mechanism is blocked. 7. The possibility that the marked effects of changes in external Na+ on transmembrane Cl‐ movements in the presence of a functional anion exchange mechanism are caused by secondary effects due to changes in intracellular pH as well as to suppression of Na+, K+, Cl‐ co‐transport is discussed.
Plasma potassium changes with high intensity exercise.
Authors: Medbø J I , Sejersted O M
Published: December 2014

1. Exercise seems to change the extracellular potassium concentration far beyond the narrow limits seen in resting subjects. To examine alterations in plasma potassium concentration during exercise, twenty healthy, well‐trained men ran on the treadmill at 6 deg inclination with catheters inserted in the femoral vein and artery. 2. During 1 min exhausting exercise plasma potassium concentration rose in parallel in the vein and artery, reaching peak post‐exercise values of 8.34 +/‐ 0.23 mmol l‐1 and 8.17 +/‐ 0.29 mmol l‐1. After 3 min recovery the potassium concentration was 0.50 +/‐ 0.05 mmol l‐1 below pre‐exercise values. Both the rise of plasma potassium concentration during exercise and the decline during recovery followed exponential time courses with a half‐time of 25 s. 3. Exercise at reduced intensity showed that the peak post‐exercise potassium concentration was linearly related to the exercise intensity. Individual resting, peak and nadir values were proportionally related. 4. The increased potassium concentration during exercise can be explained in full by the electrical activity in the exercising muscles. Repeated 1 min exhausting exercise bouts revealed no relationship between potassium concentration and plasma pH nor glycogen break‐down. 5. All of the observations fit a simple model of potassium efflux from active muscle and elimination from blood with the following characteristics: the efflux increases (decreases) stepwise at the onset (end) of exercise, and the efflux rate during exercise increases with exercise intensity. Potassium is eliminated from blood by a proportional regulator which may be the Na(+)‐K+ pump of the exercising muscle. Extracellular potassium is indirectly linked to the pump stimulus, and the rate of reuptake is proportional to the extracellular accumulation. Thus no limited maximal power for potassium uptake was found. The post‐exercise undershoot of 0.5 mmol l‐1 can be explained by a higher gain of the pump after exercise. 6. The large, rapid changes in the plasma potassium concentration during and after exercise is due to the first order kinetics of the reuptake mechanism rather than to a limited power to take up potassium.
Selective action of myasthenic syndrome antibodies on calcium channels in a rodent neuroblastoma x glioma cell line.
Authors: Peers C , Lang B , Newsom‐Davis J , Wray D W
Published: December 2014

1. The effect of Lambert‐Eaton myasthenic syndrome (LEMS) immunoglobulin G (IgG) on Ca2+ channels in undifferentiated mouse neuroblastoma x rat glioma hybrid cells (NG 108 15) was studied using the whole‐cell patch clamp technique. 2. Sustained inward Ca2+ channel currents were evoked by depolarizing pulses from holding potentials of ‐80 and ‐40 mV, and were blocked by 5 microM‐nitrendipine (L‐type currents). Transient inward Ca2+ channel currents were activated from a holding potential of ‐80 mV by small depolarizing steps (T‐type currents). Noradrenaline (10 microM) was without effect on transient currents. 3. LEMS IgG selectively reduced sustained (L‐type) Ca2+ channel current amplitudes evoked from either holding potential used. In the presence of nitrendipine (5 microM), there was no significant effect of LEMS IgG on the remaining transient (T‐type) Ca2+ channel current amplitudes. 4. Studies of the potential for maximal inward current indicated that voltage sensitivities of both L‐ and T‐type Ca2+ channel current amplitudes were unaffected by LEMS IgG, whether recorded in the presence or absence of nitrendipine. LEMS IgG had no significant effect on the time‐to‐peak or decay of Ca2+ channel currents. 5. It is concluded that LEMS IgG acts selectively to cause functional loss of L‐type, but not T‐type, Ca2+ channels in NG 108 15 cells. Any effect of LEMS IgG on N‐type channels (not present in these undifferentiated cells) was not studied here. LEMS IgG also acts at motor nerve terminal Ca2+ channels leading to muscle weakness. Thus antigenic similarities must exist between L‐type channels in NG 108 15 cells and Ca2+ channels at motor nerve terminals.
Effects of gallopamil on calcium release and intramembrane charge movements in frog skeletal muscle fibres.
Authors: Feldmeyer D , Melzer W , Pohl B
Published: December 2014

1. Intramembrane charge movements and changes in intracellular Ca2+ concentration were studied in voltage clamp experiments on cut twitch muscle fibres of the frog. The restoration from inactivation caused by steady depolarization and its modification by the phenylalkylamine Ca2+ channel antagonist gallopamil (D600, 10‐30 microM) were investigated. 2. D600 prevented the restoration from inactivation of Ca2+ release which normally occurred at ‐80 mV. In D600 Ca2+ release recovered from inactivation at ‐120 mV. 3. D600 did not alter the characteristics of intramembrane charge movements in the depolarized fibre (charge 2) but the increase in the amount of mobile charge in the test voltage range above ‐60 mV, which normally occurs after changing the holding potential to ‐80 mV, was suppressed. The charge movement characteristics of D600‐paralysed fibres, which were held at ‐80 mV, equalled those of normal depolarized and inactivated fibres. 4. Control records for the charge movement analysis were always obtained by voltage steps above 0 mV. Using the ‘conventional’ control in the potential range between ‐80 and ‐160 mV led to an underestimation and a kinetic deformation of charge movements in D600‐treated fibres, which was due to various amounts of nonlinear charge in the control. 5. Like the restoration of Ca2+ release at ‐80 mV in normal fibres the recovery from paralysis at ‐120 mV in D600‐treated fibres was accompanied by a significant increase in mobile charge in the potential range positive of ‐60 mV. Both Ca2+ release and charge movement at test potentials above ‐60 mV recovered with almost identical time course. 6. Restoration of Ca2+ release at a holding potential of ‐80 mV in normal fibres or at ‐120 mV in D600‐treated fibres could not be clearly correlated to charge movement changes in the voltage range negative of ‐60 mV (charge 2). 7. Our results are consistent with a voltage‐dependent inhibitory effect of D600 on the charge displacement that controls Ca2+ release from the sarcoplasmic reticulum but provide little evidence for a conversion of charge 2 into the charge that is involved in the control of Ca2+ release.
The descending limb of the force‐sarcomere length relation of the frog revisited.
Authors: Granzier H L , Pollack G H
Published: December 2014

1. We studied the descending limb of the force‐sarcomere length relation in single frog muscle fibres using sarcomere isometric contractions. 2. Sarcomere length was measured simultaneously with two independent methods: a laser diffraction method and a segment length method that detects the distance between two markers attached to the surface of the fibre, about 800 microns apart. Both methods were used to keep sarcomeres at constant length during contraction. 3. Fibres were selected for low resting tension since it was known from previous experiments that for such fibres the force developed by fixed‐end tetani is much higher than that predicted by the degree of filament overlap. 4. With fixed‐end tetani, force decline with increase of sarcomere length was small between 2.0 and 3.0 microns. At a sarcomere length of 3.0 microns, force was about 90% of maximal. 5. With sarcomere isometric tetani, force was considerably lower than with fixed‐end tetani. Force was maximal at about 2.1 microns and decreased to zero at about 3.6 microns. At intermediate lengths the descending limb was within 80 nm of the values predicted from filament overlap. 6. We investigated why force of fixed‐end contractions was much higher than that generated by sarcomere isometric contractions. 7. During the force plateau of fixed‐end tetani at sarcomere lengths longer than about 2.0‐2.2 microns, sarcomeres in the fibres mid‐region were not isometric, but instead stretched slowly. By measuring the force‐velocity relation it was shown that this slow stretch elevates active force well beyond sarcomere isometric force. 8. Stretch of the central region was also observed during the tetanic force rise. This was shown to result in an increase of passive force that grew larger at longer sarcomere lengths. At about 3.6 microns the increase of passive force was similar to the total force generated by fixed‐end contractions at this length. 9. Laser diffraction and segment length methods gave the same results, diminishing the chance that any systematic artifact underlies our findings. 10. While earlier experiments from this laboratory carried out on fibres held at constant length during contraction did not reveal a linear descending limb, the present results support the linear descending limb as a characteristic feature of isometrically contracting sarcomeres.
Membrane potential dependence of intracellular pH regulation by identified glial cells in the leech central nervous system.
Authors: Deitmer J W , Szatkowski M
Published: December 2014

1. We have measured the intracellular pH (pHi) and membrane potential of identified glial cells in the central nervous system of the leech, Hirudo medicinalis, using double‐barrelled pH‐sensitive microelectrodes. 2. When extracellular K+ concentration was increased, the glial membrane potential decreased and pHi increased; lowering the extracellular K+ concentration hyperpolarized the glial membrane and decreased pHi. These pHi changes were largely dependent upon the presence of CO2‐HCO3‐; in nominally CO2‐HCO3(‐)‐free saline solution, they were 50‐80% smaller. 3. The steady‐state pHi of the glial cells in CO2‐HCO3(‐)‐buffered saline solution strongly correlated with the membrane potential between ‐40 and ‐90 mV. The slope of this relationship was 60 mV/pH unit. 4. The neurotransmitter 5‐hydroxytryptamine (50 microM), which hyperpolarizes the glial membrane, also produced a large, CO2‐HCO3(‐)‐dependent decrease in pHi. The size of the pHi change depended upon the amplitude of the membrane hyperpolarization. 5. The increase in pHi produced by the membrane depolarization in 20 mM‐K+ was abolished in Na(+)‐free saline. Removal of external Na+ in the presence of 20 mM‐K+ reversed the pHi increase. 6. The pHi increase in 20 mM‐K+ was also inhibited by the stilbene 4,4‐diisothiocyanostilbene‐2'‐disulphonic acid (DIDS, 0.5 mM). In a DIDS‐poisoned preparation a small decrease of pHi was observed in 20 mM‐K+ both in the presence and nominal absence of CO2‐HCO3‐. 7. In neurones, neither CO2‐HCO3‐ nor 20 mM‐K+ produced an intracellular alkanization. The steady‐state pHi of several identified neurones was not correlated with the membrane potential. 8. We conclude that in glial cells, but not in neurones, the pHi is dependent upon the membrane potential. This membrane potential dependence is due to the activity of the electrogenic Na(+)‐HCO3‐ co‐transporter in the glial cell membrane.
Effects of glycine and GABA on isolated bipolar cells of the mouse retina.
Authors: Suzuki S , Tachibana M , Kaneko A
Published: December 2014

1. Bipolar cells were enzymatically (papain) dissociated from the mouse retina. Responses to exogenously applied glycine and GABA were recorded using the whole‐cell voltage clamp method (pipette solution contained 121 mM‐Cl‐). Both glycine and GABA evoked inward currents in cells voltage clamped at negative membrane voltages (e.g. ‐60 mV) and superfused with the control solution containing 146 mM‐Cl‐. 2. Polarities of both glycine‐ and GABA‐induced currents reversed near 0 mV under our control conditions. The reversal potential depended on both external [( Cl‐]o) and internal (intrapipette; [Cl‐]p) Cl‐ concentrations, but on neither Na+ nor K+ concentration. The reversal potentials were very close to the calculated equilibrium potential for Cl‐ estimated by using the Nernst equation with various external and internal Cl‐ activities. 3. The sensitivity to both glycine and GABA was highest at the axon terminal bulb. 4. Glycine‐induced responses were antagonized by 10 nM‐strychnine (competitively and non‐competitively), but by neither bicuculline nor picrotoxin. GABA‐induced responses were antagonized by 30 microM‐bicuculline (competitively) and 30 microM‐picrotoxin (non‐competitively), but not by 100 nM‐strychnine. Muscimol was as effective as GABA. Baclofen evoked no response even at 100 microM and did not modulate voltage‐dependent Ca2+ current. Pentobarbitone (10 microM) increased the sensitivity to GABA. These observations suggest that glycine and GABA worked on separate receptor molecules and that the receptors for GABA were GABAA type. 5. The present study suggests that glycine and GABA, both putative neurotransmitters of amacrine cells, mediate inhibition of bipolar cells in the mouse retina.
Ionic permeabilities of the cell membranes of sheep tracheal epithelium.
Authors: Acevedo M , Olver R E , Ward M R
Published: December 2014

1. The ionic permeabilities of the apical and basolateral membranes of sheep tracheal epithelial cells have been evaluated by studying the effect of ion replacements on the apical (Va) and basolateral (Vb) membrane potentials and apical voltage divider ratio (fa). 2. The results provide evidence for the existence of conductances for Cl‐, Na+ and K+ at the apical membrane, and of an important K+ conductance at the basolateral membrane. These characteristics agree with the model for Cl‐ secretion and Na+ absorption proposed for tracheal epithelium of other species. 3. The short‐circuit current (Isc) across this tissue was found to increase significantly when HCO3‐ and CO2 were added to the bathing solutions. The addition of 0.5 mM‐SITS (4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid) to the serosal bathing solution decreased Isc only if HCO3‐ and CO2 were present in the bathing solutions. These results suggest the existence of a HCO3‐ secretion in sheep tracheal epithelium under short‐circuit conditions. 4. The results obtained in HCO3‐ replacement studies are compatible with an electrically silent HCO3‐ entry across the basolateral membrane and an electrogenic exit at the apical membrane of the cells.
Force‐velocity relation of frog skeletal muscle fibres shortening under continuously changing load.
Authors: Iwamoto H , Sugaya R , Sugi H
Published: December 2014

1. The force‐velocity (P‐V) relation of single frog skeletal muscle fibres was examined in non‐steady‐state conditions in which the load on the fibre changed continuously with time. Two such types of condition were used; in one type, the load was increased from zero to the maximum isometric force (P0) (auxotonic condition), while in the other type the load was decreased form P0 to zero at constant rates (ramp decrease in load). 2. The P‐V curves obtained in the auxotonic condition were convex upwards and always below the hyperbolic P‐V curve obtained in the isotonic condition. Different curves were obtained depending on the compliance of auxotonic load. The shortening velocity for a given amount of load increased with increasing compliance. 3. Qualitatively similar P‐V relations were obtained irrespective of whether the fibre was made to shorten auxotonically at the onset of stimulation or after the development of P0. 4. If the force at any time after the onset of auxotonic shortening was normalized relative to the isometric force at the same time after the onset of isometric force development, the normalized force versus velocity curves were found to fit well to the hyperbolic P‐V curve in the isotonic condition except for the low‐force region. 5. The P‐V curves obtained during the ramp decrease in load were hyperbolic in shape except for the humps at the high‐force region and always above the P‐V curve in the isotonic condition. Different curves were obtained depending on the rate of load decrease. The maximum shortening velocity increased with increasing rate of load decrease. 6. The above features of the P‐V relations could well be simulated by a simplified Huxley contraction model, indicating that the kinetic properties of the cross‐bridges are the same in both steady‐ and non‐steady‐state conditions.
Fusimotor control of muscle spindle sensitivity during respiration in the cat.
Authors: Greer J J , Stein R B
Published: December 2014

1. The two types of fusimotor neurones, dynamic and static, can be differentiated by their effects on muscle spindle afferents. We have recorded the activity of muscle spindle primary afferents from the intercostal nerves of anaesthetized or decerebrate cats. A 4 Hz sinusoidal stretch was applied to the muscle containing the spindles of interest before and after crushing the nerve proximal to the recording site to eliminate fusimotor effects. The relative activity of the dynamic and static fusimotor neurones was inferred from the change in the spindle afferents' response. 2. Some areas of intercostal muscle normally showed phasic activity linked to respiration, where as other areas of intercostal muscle showed no EMG activity under our experimental conditions. In areas of intercostal muscle lacking EMG activity, the afferents' mean rate was higher and the modulation around the mean was lower at all phases of the breathing cycle when the efferent supply was intact. This result suggests the muscle spindles were receiving a steady level of static fusimotor activity. 3. Spindle primary afferents from regions of intercostal muscle that were typically recruited during respiration had an additional increase in mean rate and modulation around the mean rate in phase with the EMG activity. This is suggestive of phasic activation of dynamic fusimotor neurones in addition to static fusimotor discharge. 4. Thus, the two types of fusimotor neurones can be activated separately by the CNS to control the sensitivity of muscle spindles. The regional differences in the recruitment patterns of fusimotor neurones parallels the functional specializations of different areas of the intercostal muscles. The temporal modifications of fusimotor activity during each respiratory cycle means that the segmental reflex gain will vary in those intercostal muscles that are active during respiration. 5. These findings regarding the CNS recruitment of the two types of fusimotor neurones during respiration are similar to those reported for the hindlimb extensors during locomotion, but differ from those reported for jaw muscles during chewing. This may reflect differing control strategies being used by the CNS to meet the unique demands of the various rhythmical movements.
Synchronization of motor unit activity during voluntary contraction in man.
Authors: Datta A K , Stephens J A
Published: December 2014

1. Motor unit synchronization has been studied in human first dorsal interosseous muscle. 2. Two needle electrodes were inserted into the muscle and the activity of pairs of motor units recorded. 3. Pre‐ and post‐stimulus histograms of the firing of unit pairs showed a narrow central peak of duration 1.3‐9.3 ms (88% of sample in the range 1‐6 ms; mode 3.0 ms), together with a variable amount of synchronization of somewhat longer duration. 4. For the duration of the whole synchronization peak (85% sample in range 5‐15 ms; mode between 6.1 and 8.0 ms (31% of sample], units fired between 8 and 485% times more often than would have been expected had the units been firing independently of one another. Amplitudes of the peak of the recorded histograms expressed as a proportion of control ranged from 1.8 to 10.9 (mean 3.9; bin width 160 microseconds). 5. The strength of synchronization between the firing of motor unit pairs was inversely related to differences in recruitment threshold. The largest amount of synchronization was observed for pairs of units in which both had recruitment thresholds less than 0.5 N or greater than 1.0 N. Less synchronization was found between pairs of units in which one had a recruitment threshold less than 0.05 N and the other a threshold greater than 1.0 N. 6. The time course of synchronization was well matched by the predictions of a theoretical model based on the hypothesis that underlying the observed synchronization is the joint arrival of EPSPs from branched last‐order input fibres.
Sympathetic discharges in the human supraorbital nerve and their relation to sudo‐ and vasomotor responses.
Authors: Nordin M
Published: December 2014

1. Sympathetic nerve activity occurring as bursts of multi‐unit impulses was recorded with tungsten microelectrodes in the supraorbital nerve of awake healthy subjects. Within the fascicular innervation zone on the forehead, skin resistance was measured as an indicator of sweat gland activity, and skin blood flow was measured with laser‐doppler flowmetry. 2. At room temperature, there was little or no background burst activity, but arousal stimuli or mental stress evoked bursts followed by a vasodilator response. Provided repeated arousal stimuli were delivered, individual bursts were followed by a decrease in skin resistance. 3. Body heating induced increasing background burst activity. After an initial period without associated electrodermal activity, there were decreases in skin resistance, which showed a positive linear correlation with the amplitude of the preceding burst. Individual bursts were followed by a vasodilator response with an average onset latency of 2.8 s and an average duration of 9.1 s, and rapid increases in blood flow coincided with a marked increase in burst activity. Arousal stimuli evoked bursts followed by both vasodilator and skin resistance responses. 4. During body cooling, there was no background burst activity, but signs of relatively weak, probably neurally mediated vasoconstriction were observed and arousal‐evoked bursts were reduced or abolished, as were the associated vasodilator and skin resistance responses. 5. It is concluded that body heating induces active sympathetic vasodilatation in the skin of the human forehead, and that this is either sudomotor‐mediated or caused by vasodilator fibres firing in synchrony with sudomotor fibres. A similar sympathetic mechanism probably underlies the vasodilator responses evoked by arousal stimuli and mental stress.
Effects of external tetraethylammonium ions and quinine on delayed rectifying K+ channels in mouse pancreatic beta‐cells.
Authors: Bokvist K , Rorsman P , Smith P A
Published: December 2014

1. The whole‐cell and outside‐out patch configurations of the patch‐clamp technique were used to study the mechanisms of block produced by external tetraethylammonium ions (TEA+) and quinine on delayed rectifying K+ channels in mouse pancreatic beta‐cells. 2. In whole‐cell recordings, TEA+ blocks the delayed outward current (which reflects the activity of delayed rectifying K+ channels by greater than 85%) in a concentration‐dependent manner. The block appeared to be 1:1 with a Kd of approximately 1.4 mM at a membrane potential of 0 mV. The value of Kd varied with the membrane potential and there was an e‐fold increase for a 70 mV depolarization. 3. Single‐channel recordings revealed that delayed rectifying K+ channels have a unitary conductance of 8.5 pS ([K+]1 = 155 mM; [K+]o = 5.6 mM) and a single‐channel K+ permeability of 2.8 X 10(‐14) cm3 s‐1. 4. First latency histograms of channel openings during voltage pulses from ‐70 to 0 mV peaked after 4 ms. A reaction scheme involving two closed states adequately but not perfectly described the distribution of the first latencies. The openings of the channels were grouped in bursts and the distribution of the closed times required two exponentials with time constants of 2.0 and 13 ms, respectively. The distribution of the open times could be described by a single exponential with a time constant of 25 ms. 5. Channel block produced by TEA+ (1 mM) was associated with a 40% decrease of the single‐channel current amplitudes and a reduction in single‐channel K+ permeability to 1.9 X 10(‐14) cm3 s‐1 but did not measurably affect the single‐channel kinetics suggesting that the blocking reaction is very rapid. 6. Quinine blocked the whole‐cell delayed outward current in a concentration‐dependent manner. Half‐maximal inhibition was attained at approximately 4 microM and the binding appeared to be 2:1. 7. Single‐channel recordings indicated that the inhibition produced by quinine (10 microM) resulted from a decrease in the duration of the openings to a mean value of 6.7 ms. The time constants for the distribution of the closures were increased by approximately 30%. Quinine did not affect the amplitude of the openings. The rate constant of the blocking reaction (kB) was 15 mM‐1 ms‐1 at 0 mV.
The effects of metabolic inhibition on uterine metabolism and intracellular pH in the rat.
Authors: Wray S
Published: December 2014

1. Uterine metabolism was studied in pregnant and non‐pregnant rats by measuring high energy phosphates and intracellular pH (with 31‐phosphorus nuclear magnetic resonance (31P NMR) spectroscopy) and lactic acid efflux. Isolated, superfused uteri were investigated during control conditions (30 degrees C) and in the presence of metabolic inhibitors and high [K+]. 2. In control conditions the ratio of phosphocreatine and ATP concentrations ([PCr]/[ATP]) was higher in the pregnant (0.88 +/‐ 0.09) than the non‐pregnant uterus (0.52 +/‐ 0.04). When oxidative phosphorylation was inhibited by cyanide, there was a significant (P less than 0.01) decrease in [PCr] and [ATP] and an increase in the concentration of inorganic phosphate ([Pi]). These changes were greater in the non‐pregnant than the pregnant uterus. 3. There was no difference in the mean value of resting pHi found in pregnant and non‐pregnant uterus (7.19 +/‐ 0.04 and 7.17 +/‐ 0.03, external pH 7.4, n = 10 and 12 respectively). There was a significant intracellular acidification in both pregnant (0.31 +/‐ 0.04 pH unit) and non‐pregnant (0.27 +/‐ 0.02 pH unit) uterine tissue in the presence of cyanide. These effects of cyanide on metabolites and pHi were fully reversed upon return to control solutions. 4. When both aerobic and anaerobic glycolysis were blocked by iodoacetate, there was a rapid disappearance of high energy phosphates from the 31P NMR spectrum and a large increase in the phosphomonoester spectral region, where sugar phosphate intermediates of glycolysis resonate. These changes were seen in both pregnant and non‐pregnant uteri and were irreversible. 5. Lactate production was detected, in the presence of oxygen, in both pregnant and non‐pregnant preparations (0.43 +/‐ 0.07 and 0.25 +/‐ 0.09 mumols g‐1 min‐1, respectively). In both preparations the rate of lactate production was markedly increased in the presence of cyanide. The increase was much more marked in non‐pregnant (approximately 10‐fold) than pregnant (approximately 5‐fold) uteri, resulting in a very similar rate of lactate efflux in cyanide. 6. When lactate efflux in non‐pregnant uteri was blocked by alpha‐cyano‐4‐hydroxycinnamate, there was a significant acidification (0.21 +/‐ 0.04 pH unit, n = 6). The addition of cyanide produced a more pronounced acidification (0.34 +/‐ 0.04 pH unit) than that seen with either cyanide or alpha‐cyano‐4‐hydroxycinnamate alone.(ABSTRACT TRUNCATED AT 400 WORDS)
Vasoactive intestinal peptide stimulation of human renal adenylate cyclase in vitro.
Authors: Charlton B G , Neal D E , Simmons N L
Published: December 2014

1. A direct action of vasoactive intestinal peptide (VIP) upon human kidney was sought by measurement of renal adenylate cyclase in tissue homogenates and plasma membranes isolated from tissue samples excised for therapeutic reasons. 2. VIP (1 microM) produced a mean stimulation of adenylate cyclase activity of 3.5‐fold compared to basal values in cortical plasma membranes; comparative stimulations of 2.8‐fold and 27.3‐fold were obtained with 1 microM‐glucagon and 1 microM‐h(1‐34) parathyroid hormone respectively. 3. Half‐maximal stimulation of human renal cortical plasma membrane adenylate cyclase was observed with a mean value of 35 nM‐VIP. 4. The stimulation of renal adenylate cyclase by VIP appeared to be specific because stimulation by glucagon was additive to that obtained with VIP, and the VIP receptor antagonist (4 Cl‐D‐Phe6, Leu17)‐VIP inhibited the VIP‐dependent stimulation of adenylate cyclase activity.