bluuebunny/crossref_metadata_2025 huggingface dataset:
Capillary pressure during and after incremental venous pressure elevation in man.
Authors: Mahy I R , Tooke J E , Shore A C
Published: December 2014

1. The relationship between capillary pressure and venous pressure was investigated during incremental venous pressure elevation in seven healthy volunteers. Pressure was measured simultaneously at the apex of finger nailfold capillaries and in the dorsal vein of the ipsilateral hand. Elevation of venous pressure was accomplished by inflation of a sphygmomanometer cuff around the upper arm. 2. As venous pressure rose, apical capillary pressure (Pc) approached venous pressure (Pv). For changes in Pv greater than 20 mmHg, the increment in Pc was invariably less than the increment in Pv. 3. Above a cuff pressure of 20 mmHg, capillary pulse pressure amplitude (CPPA) tended to decline. At 50 mmHg cuff pressure, CPPA was lower than at baseline for all subjects. At baseline, CPPA was 4.2 +/‐ 2.0 mmHg (mean +/‐ S.D.) and at 50 mmHg it was 2.3 +/‐ 1.1 mmHg (P = 0.02). 4. In the period between 1 and 6 min following cuff release, both Pc and CPPA were lower than at baseline. (At baseline, Pc was 16.1 +/‐ 2.3 mmHg and following cuff release it was 11.2 +/‐ 1.5 mmHg (P = 0.02). At baseline, CPPA was 4.2 +/‐ 2.0 mmHg and following cuff release it was 1.8 +/‐ 1.1 mmHg (P = 0.03).) 5. Estimated changes in the ratio of pre‐ to postcapillary resistance (Ra/Rv), using arterial blood pressure (Pa) measured in the contralateral arm, and taking (Pa‐Pc)/(Pc‐Pv) to approximate to Ra/Rv, closely mirrored changes in CPPA.(ABSTRACT TRUNCATED AT 250 WORDS)
Pacemaker current i(f) in adult canine cardiac ventricular myocytes.
Authors: Yu H , Chang F , Cohen I S
Published: December 2014

1. Single cells enzymatically isolated from canine ventricle and canine Purkinje fibres were studied with the whole‐cell patch clamp technique, and the properties of the pacemaker current i(f) compared. 2. Steady‐state i(f) activation occurred in canine ventricular myocytes at more negative potentials (‐120 to ‐170 mV) than in canine Purkinje cells (‐80 to ‐130 mV). 3. Reversal potentials were obtained in various extracellular Na+ (140, 79 or 37 mM) and K+ concentrations (25, 9 or 5.4 mM) to determine the ionic selectivity of i(f) in the ventricle. The results suggest that this current was carried by both sodium and potassium ions. 4. The plots of the time constants of i(f) activation against voltage were ‘bell shaped’ in both canine ventricular and Purkinje myocytes. The curve for the ventricular myocytes was shifted about 30 mV in the negative direction. In both ventricular and Purkinje myocytes, the fully activated I‐V relationship exhibited outward rectification in 5.4 mM extracellular K+. 5. Calyculin A (0.5 microM) increased i(f) by shifting its activation to more positive potentials in ventricular myocytes. Protein kinase inhibition by H‐7 (200 microM) or H‐8 (100 microM) reversed the positive voltage shift of i(f) activation. This effect of calyculin A also occurred when the permeabilized patch was used for whole‐cell recording. 6. These results indicate i(f) is present in ventricular myocytes. If shifted to more positive potentials i(f) could play a role in ischaemia‐induced ventricular arrhythmias. The negative shift of i(f) in the ventricle might play a role in differentiating non‐pacing regions of the heart from those regions that pace.
Effects of phosphodiesterase inhibitors on spontaneous electrical activity (slow waves) in the guinea‐pig gastric muscle.
Authors: Tsugeno M , Huang S M , Pang Y W , Chowdhury J U , Tomita T
Published: December 2014

1. The effects of the phosphodiesterase inhibitors caffeine, theophylline, isobutylmethylxanthine (IBMX) and rolipram on spontaneous electrical activity (slow waves) were studied in the circular muscle of the guinea‐pig gastric antrum. 2. All the inhibitors reduced slow wave frequency without changing the membrane potential and the slow wave configuration, but at higher concentrations they blocked the slow waves and caused membrane hyperpolarization. In the presence of the inhibitors a low level of irregular electrical activity could be observed in many preparations. 3. Isoprenaline, forskolin, dibutyryl cAMP and 8‐bromo‐cAMP all produced effects essentially similar to those of phosphodiesterase inhibitors. K+ (12 mM) and removal of K+ both depolarized the membrane and these were not affected by IBMX (1‐3 microM). A decrease in frequency caused by IBMX was also not significantly affected by 12 mM K+ or K+ removal and only partially antagonized by TEA or 4‐aminopyridine. 4. These results suggest that an increase in intracellular cAMP inhibits pacemaker activity of slow waves. An increase in K+ conductance does not seem to be a major factor in this inhibition. Slow waves appear to be a compound electrical activity in a group of muscle cells and are likely to be disintegrated by xanthine derivatives.
Subunit regulation of the neuronal alpha 1A Ca2+ channel expressed in Xenopus oocytes.
Authors: De Waard M , Campbell K P
Published: December 2014

1. Voltage‐dependent Ca2+ channels are multi‐protein complexes composed of at least three subunits: alpha 1, alpha 2 delta and beta. Ba2+ currents were recorded in Xenopus oocytes expressing the neuronal alpha 1A Ca2+ channel, using the two‐electrode voltage‐clamp technique. Various subunit combinations were studied: alpha 1A, alpha 1A alpha 2 delta b, alpha 1A beta or alpha 1A alpha 2 delta b beta. 2. The alpha 1A subunit alone directs the expression of functional Ca2+ channels. It carries all the properties of the channel: gating, permeability, voltage dependence of activation and inactivation, and pharmacology. The alpha 1A channel is activated by low voltages when physiological concentrations of the permeant cation are used. Both ancillary subunits alpha 2 delta and beta induced considerable changes in the biophysical properties of the alpha 1A current. The subunit specificity of the changes in current properties was analysed for all four beta gene products by coexpressing beta 1b, beta 2a, beta 3 and beta 4. 3. All beta subunits induce a stimulation in the current amplitude, a change in inactivation kinetics, and two hyperpolarizing shifts‐‐one in the voltage dependence of activation and a second in the voltage dependence of steady‐state inactivation. The most significant difference in regulation among beta subunits is the induction of variable rate constants of current inactivation. Rates of inactivation were induced in the following order (fastest to slowest): beta 3 > beta 1b = beta 4 > beta 2a. 4. The alpha 2 delta b subunit does not modify the properties of alpha 1A Ca2+ channels in the absence of beta subunits. However, this subunit increases the beta‐induced stimulation in current amplitude and also regulates the beta‐induced change in inactivation kinetics. 5. Of all the subunit combinations tested, Ca2+ channels that included a beta subunit were the most prone to decrease in activity. It is concluded that beta subunits are the primary target for the inhibitory mechanisms involved in Ca2+ channel run‐down. 6. Both alpha 2 delta b and beta 1 b subunits slightly modified the sensitivity of the alpha 1A subunit to the snail peptide omega‐conotoxin MVIIC. 7. The subunit‐induced changes in properties of the alpha 1A channel are surprisingly similar to changes reported for other alpha 1 subunits. These modifications in channel activity should therefore represent important functional landmarks in the on‐going characterization of subunit‐subunit interactions.
GABAB receptor‐mediated presynaptic inhibition in guinea‐pig hippocampus is caused by reduction of presynaptic Ca2+ influx.
Authors: Wu L G , Saggau P
Published: December 2014

1. The hypothesis that activation of GABAB receptors inhibits evoked synaptic transmission by reducing the presynaptic Ca2+ influx was tested using a recently developed technique for simultaneously recording the presynaptic Ca2+ transient ([Ca2+]t) and the field excitatory postsynaptic potential (fEPSP) evoked by a single electrical stimulus at CA3 to CA1 synapses of guinea‐pig hippocampus. 2. The GABAB receptor agonist baclofen reversibly blocked, in a dose‐dependant manner, both the fEPSP and the presynaptic [Ca2+]t with similar time courses. During application of baclofen, the fEPSP was proportional to about the fourth power of the presynaptic [Ca2+]t, and the presynaptic fibre volley and the resting Ca2+ level did not change. These results are similar to those we previously observed following application of several voltage‐dependent Ca2+ channel blockers, suggesting that baclofen inhibits the fEPSP by blocking the presynaptic Ca2+ influx. 3. The inhibition by baclofen of both the fEPSP and the presynaptic [Ca2+]t was blocked by the GABAB receptor antagonist CGP 35348, consistent with the causal relationship between the GABAB receptor‐mediated presynaptic inhibition of the [Ca2+]t and the fEPSP. 4. The inhibition by baclofen of the [Ca2+]t was partially occluded by application of the voltage‐dependent Ca2+ channel blocker omega‐conotoxin‐GVIA (omega‐CgTX‐GVIA), but not omega‐agatoxin‐IVA (omega‐AgaTX‐IVA), suggesting that baclofen reduces the presynaptic [Ca2+]t by blocking Ca2+ channels including the omega‐CgTX‐GVIA‐sensitive type. 5. We conclude that baclofen inhibits evoked transmitter release by reducing presynaptic Ca2+ influx.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of calcium‐activated non‐selective cation channel activity by nitric oxide in rat brown adipose tissue.
Authors: Koivisto A , Nedergaard J
Published: December 2014

1. Single‐channel calcium‐activated non‐selective cation currents from isolated rat brown fat cells were measured using the inside‐out patch configuration of the patch‐clamp technique. The existence of a possible modulatory effect of nitric oxide on the putative redox‐modulatory site located on the intracellular side of the non‐selective cation channel was investigated. 2. The nitric oxide‐releasing substances nitroglycerin, sodium nitroprusside, S‐nitrosocysteine and S‐nitroso‐N‐acetyl‐D,L‐penicillamine (all at 100 microM) were able to block channel activity almost completely. 3. In each case the blockade was persistent and could not be washed away. Dithiothreitol (DTT, 2 mM) was able to reverse the blockade to a large extent, whereas oxidized DTT (2 mM) was without effect. 4. It was concluded that nitric oxide can modulate non‐selective cation channel activity by oxidizing sulfhydryl groups and that this effect can be reversed by reduction.
ATP‐operated calcium‐permeable channels activated via a guanine nucleotide‐dependent mechanism in rat macrophages.
Authors: Naumov A P , Kiselyov K I , Mamin A G , Kaznacheyeva E V , Kuryshev Y A , Mozhayeva G N
Published: December 2014

1. To elucidate the possible involvement of a G protein in ATP‐evoked Ca(2+)‐permeable channel activity, membrane currents of rat peritoneal macrophages were recorded using inside‐out and cell‐attached configurations of the patch clamp technique. 2. In inside‐out experiments with a pipette solution containing 105 mM Ba2+, application of 100 microM GTP or GTP gamma S to the internal surface of the membrane elicited a rise in channel activity. This effect was observed in 49% of the patches investigated (n = 69). The mean value of NPo (N, number of open channels; Po, channel open probability) was equal to 0.49 +/‐ 0.27 (mean +/‐ S.E.M.; n = 16). The delay in the activity development was 21 +/‐ 8 s (n = 18) with 200 microM ATP added to the pipette solution and about 4 min (n = 5) without agonist in the pipette. Similar results were obtained with 10 mM Ca2+ as the only permeant cation. 3. Properties of GTP gamma S‐evoked channels were identical to those of channels activated by extracellular application of ATP. The channels exhibited at least four conductance sublevels, the 4th one being the least frequent. With 105 mM Ba2+ as a permeant cation, sublevel conductances were 3.5, 7, 10 and 15 pS. Corresponding values for 10 mM Ca2+ were about 4, 9, 13 and 17 pS. Extrapolated reversal potential (Er) values were about +40 and +25 mV for Ba2+ and Ca2+, respectively. 4. The activity of channels with similar characteristics could be induced by the extracellular application of fluoride in cell‐attached experiments without any agonist in the pipette solution.(ABSTRACT TRUNCATED AT 250 WORDS)
Internal Ca2+ stores involved in anoxic responses of rat hippocampal neurons.
Authors: Belousov A B , Godfraind J M , Krnjevié K
Published: December 2014

1. During whole‐cell recordings from CA1 neurons of rat brain slices with electrodes containing only KMeSO4 and Hepes, brief anoxia (2‐3 min) consistently evoked a hyperpolarization (delta V approximately 14 mV) and reduction in input resistance (delta R approximately ‐20%). 2. As in previous intracellular recordings, Dantrolene sodium (10 microM) suppressed the anoxic delta V and delta R, confirming the release of internal Ca2+ is a major component of the anoxic response. 3. To identify the relevant intracellular Ca2+ store, other blockers of Ca2+ release were applied either externally (in the bath) or internally, by addition to the contents of the recording electrode. 4. The anoxic hyperpolarization was abolished or much reduced by heparin (10‐20 micrograms ml‐1, internal), thapsigargin (10 microM, external), Ruthenium Red (50 microM, internal) and external procaine (0.5‐2 mM), but not by internal procaine (0.5‐1 mM) or ryanodine (10 microM, external). 5. The anoxic fall in resistance was also abolished or reduced by heparin, thapsigargin and external procaine, but not by ryanodine, internal procaine or Ruthenium Red. 6. In addition, external procaine (0.5‐2 mM) eliminated the early (transient) depolarization and reduced the post‐anoxic hyperpolarization by 60 +/‐ 22%. 7. None of these agents consistently changed the resting potential, but the input resistance was significantly increased by Dantrolene and external procaine. 8. In view of the marked effects of heparin and thapsigargin, but not ryanodine and internal procaine, we conclude that the anoxic response seen in such whole‐cell recordings is initiated predominantly by Ca2+ release from an internal store that is InsP3 sensitive rather than Ca2+ sensitive. 9. Comparable but less pronounced effects of external procaine were seen during intracellular recordings with 3 M KCl‐containing electrodes. The dose‐dependent suppression of various features of the anoxic response by external procaine (EC50 approximately 0.2 mM) is presumed to be mediated by a superficial membrane trigger or modulating site.
A highly calcium‐selective cation current activated by intracellular calcium release in MDCK cells.
Authors: Delles C , Haller T , Dietl P
Published: December 2014

1. The whole‐cell patch clamp technique and fluorescence microscopy with the Ca2+ indicators fura‐2 and fluo‐3 were used to measure the whole‐cell current and the free intracellular Ca2+ concentration ([Ca2+]i) in Madin‐Darby canine kidney (MDCK) cells. 2. In a Ca(2+)‐free bath solution, thapsigargin (TG) caused a transient increase of [Ca2+]i. Subsequent addition of Ca2+ caused a long lasting elevation of [Ca2+]i. 3. In a Ca(2+)‐free bath solution, extracellular application of TG, ATP or ionomycin, or intracellular application of inositol 1,4,5‐trisphosphate (IP3), caused a small but significant inward current (Iin) and a transient outward Ca(2+)‐dependent K+ current (IK(Ca)), consistent with intracellular Ca2+ release. Subsequent addition of Ca2+ induced a prominent Iin with a current density of ‐4.2 +/‐ 0.7 pA pF‐1. This Iin was unaffected by inositol 1,3,4,5‐tetrakisphosphate (IP4). 4. Na+ replacement by mannitol, N‐methyl‐D‐glucamine+ (NMG+), aminomethylidin‐trimethanol+ (Tris+) or choline+ reduced Iin by 54, 65, 52 and 56%, respectively. This indicates an apparent Ca2+ selectivity over Na+ of 26:1. Iin was, however, unaffected by replacing Cl‐ with gluconate‐ or by the K+ channel blocker charybdotoxin (CTX). 5. Iin was completely blocked by La3+ (IC50 = 0.77 microM). Consistently, La3+ completely reversed the TG‐induced elevation of [Ca2+]i. SK&F 96365 (1‐[3‐(4‐methoxyphenyl)‐propoxyl]‐1‐(4‐methoxy‐phenyl)‐ethyl‐1H‐im idazole) HCl did not inhibit the TG‐induced Iin. It did, however, exhibit a biphasic effect on [Ca2+]i, consisting of an initial Ca2+ decay and a subsequent Ca2+ elevation. La3+ completely reversed the SK&F 96365‐induced elevation of [Ca2+]i. 6. In the absence of Na+, Iin was dependent on the bath Ca2+ concentration (EC50 = 1.02 mM). Ca2+ replacement by Ba2+ or Mn2+ resulted in a reduction of Iin by 95 and 94%, respectively. 7. From these experiments we conclude that Ca2+ release from intracellular Ca2+ stores, induced by different independent methods, stimulates La(3+)‐inhibitable Ca2+ entry in MDCK cells. Ca2+ entry is at least, in part, mediated by a cation current, which is highly, but not exclusively, selective for Ca2+ over Na+ and insensitive to SK&F 96365.
Non‐uniform conduction time in the olivocerebellar pathway in the anaesthetized cat.
Authors: Aggelopoulos N C , Duke C , Edgley S A
Published: December 2014

1. It has recently been demonstrated that conduction velocities of cerebellar climbing fibre afferents in the rat are tuned according to fibre length such that conduction time between their origin in the inferior olive and their target cortical Purkinje cells is constant. Here we have examined the situation in the cat, where individual climbing fibres are substantially longer. Complex spike responses of Purkinje cells located at various depths in the vermis (zones a and b) were evoked by electrical stimulation of olivocerebellar fibres close to their origin and were recorded either extra‐ or intracellularly. 2. The onset latencies of directly evoked complex spikes ranged from 2.6 to 6.9 ms. A consistent trend in each electrode penetration was that the complex spike latencies were longer for the superficially encountered cells (where olivocerebellar fibre length is greatest) and shorter for deeper cells (where olivocerebellar fibre length is shorter). 3. Linear regression analysis suggests that conduction time in olivocerebellar fibres in the cat is not fixed but varies linearly with conduction distance. Our findings would be consistent with a uniform conduction velocity in olivocerebellar fibres of about 6.6 m s‐1.
Skin strain patterns provide kinaesthetic information to the human central nervous system.
Authors: Edin B B , Johansson N
Published: December 2014

1. We investigated the contribution of skin strain‐related sensory inputs to movement perception and execution in five normal volunteers. The dorsal and palmar skin of the middle phalanx and the proximal interphalangeal (PIP) joint were manipulated to generate specific strain patterns in the proximal part of the index finger. To mask sensations directly related to this manipulation, skin and deeper tissues were blocked distal to the mid‐portion of the proximal phalanx of the index finger by local anaesthesia. 2. Subjects were asked to move their normal right index finger either to mimic any perceived movements of the anaesthetized finger or to touch the tip of the insentient finger. 3. All subjects readily reproduced actual movements induced by the experimenter at the anaesthetized PIP joint. However, all subjects also generated flexion movements when the experimenter did not induce actual movement but produced deformations in the sentient proximal skin that were similar to those observed during actual PIP joint flexion. Likewise, the subjects indicated extension movement at the PIP joint when strain patterns corresponding to extension movements were induced. 4. In contrast, when the skin strain in the proximal part of the index finger was damped by a ring applied just proximal to the PIP joint within the anaesthetized skin area, both tested subjects failed to perceive PIP movements that actually took place.(ABSTRACT TRUNCATED AT 250 WORDS)
Activation of the plasma membrane chloride channel by protein kinase C in isolated guinea‐pig hepatocytes.
Authors: Koumi S , Sato R , Aramaki T
Published: December 2014

1. To assess the nature of the underlying mechanism of noradrenaline‐induced increase of Cl‐ conductances in hepatocytes, macroscopic and unitary currents through noradrenaline‐induced Cl‐ channels were examined in enzymatically isolated guinea‐pig hepatocytes using whole‐cell, cell‐attached and excised inside‐out configurations of the patch‐clamp technique. 2. When K+ conductances were blocked and the intracellular Ca2+ concentration ([Ca2+]i) was set at 0.1 microM, bath application of noradrenaline activated the time‐independent membrane currents under whole‐cell voltage‐clamp conditions. The current was similarly activated by phorbol ester (PMA), an activator of protein kinase C (PKC), while a specific protein kinase C inhibitor, H‐9, reversed PMA activation of the current. The inactive phorbol ester, 4 alpha‐phorbol 12‐myristate, 13‐acetate (alpha PMA), failed to activate the channel. 3. The reversal potential of the PMA‐activated current shifted by approximately 60 mV per 10‐fold change in the external Cl‐ concentration, indicating that the current was Cl‐ selective. Bath application of 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS) partially inhibited both the noradrenaline‐ and PMA‐induced currents. 4. In single channel recordings from cell‐attached patches, bath application of noradrenaline or PMA induced unitary current activity, the averaged slope conductance of which was 10.1 +/‐ 1.5 pS (mean +/‐ S.D.; n = 12) in the noradrenaline‐induced current and 9.7 +/‐ 1.3 pS (n = 7) in the PMA‐induced current. The open time distribution was moderately well fitted by a single exponential function with mean open lifetime of 88.5 +/‐ 10.6 ms (n = 10), while at least two exponentials were required to fit the closed time distributions with a time constant for the fast component of 24.4 +/‐ 5.8 ms (n = 10) and for the slow component of 316.9 +/‐ 49.2 ms (n = 10). 5. Bath application of purified PKC to excised inside‐out patches activated the channel. The PKC selective inhibitor, PKC(19‐36), and DIDS inhibited the PKC‐activated channel. 6. These results suggest that PKC can phosphorylate the channel protein or a related structure leading to the activation of Cl‐ channels in guinea‐pig hepatocytes.
Comparison of energy output during ramp and staircase shortening in frog muscle fibres.
Authors: Linari M , Woledge R C
Published: December 2014

1. We compared the rates of work and heat production during ramp shortening with those during staircase shortening (sequence of step releases of the same amplitude, separated by regular time intervals). Ramp or staircase shortening was applied to isolated muscle fibres (sarcomere length, 2.2 microns; temperature, approximately 1 degree C) at the plateau of an isometric tetanus. The total amount of shortening was no greater than 6% of the fibre length. 2. During ramp shortening the power output showed a maximum at about 0.8 fibre lengths per second (Lo s‐1), which corresponds to 1/3 the maximum shortening velocity (Vo). For the same average shortening velocity during staircase shortening (step size, approximately 0.5% Lo) the power output was 40‐60% lower. The rate of heat production for the same average shortening velocity was approximately 45% higher during staircase shortening than during ramp shortening. 3. The relation between rate of total energy output and shortening velocity was well described by a second order regression line in the range of velocities used (0.1‐2.3 Lo s‐1). For any shortening velocity the rate of total energy output (power plus heat rate) was not statistically different for staircase (step size, approximately 0.5% Lo) and ramp shortening. 4. The mechanical efficiency (the ratio of the power over the total energy rate) during ramp shortening had a maximum value of 0.36 at 1/5 Vo; during staircase shortening, for any given shortening velocity, the mechanical efficiency was reduced compared with ramp shortening: with a staircase step of about 0.5% Lo at 1/5 Vo the efficiency was approximately 0.2. 5. The results indicate that a cross‐bridge is able to convert different quantities of energy into work depending on the different shortening protocol used. The fraction of energy dissipated as heat is larger during staircase shortening than during ramp shortening.
Involvement of renal kallikrein in the regulation of bicarbonate excretion in rats.
Authors: Marin-Grez M , Vallés P , Odigie P I
Published: December 2014

1. The experiments reported here were performed to test the hypothesis that renal kallikrein is involved in the regulation of acid‐base balance. 2. The bicarbonate concentration and the kallikrein activity in the spontaneously voided urine of conscious rats (experiment 1) were inversely correlated (correlation coefficient (r) = ‐0.63, P < 0.0001). The correlation was even greater when the urinary bicarbonate concentration was expressed per milligram excreted creatinine (r = ‐0.74, P < 0.00002). 3. Intravenous injection of the kallikrein inhibitor aprotinin in barbiturate‐anaesthetized rats (experiment 2) reduced urinary kallikrein activity (P < 0.05) and increased bicarbonate excretion rate (P < 0.012). 4. Renal arterial infusion of aprotinin in barbiturate‐anaesthetized rats (experiment 3) reduced urinary kallikrein activity (120 min, P < 0.01), and increased bicarbonate excretion rate (120 min, P < 0.01). Animals infused with the inhibitor developed a moderate metabolic acidosis (base excess: control, 2.9 +/‐ 0.7 mM (mean +/‐ S.E.M.); experimental, ‐8.1 +/‐ 0.7 mM; P < 0.05). 5. The bicarbonate concentration of urine fractions obtained after retrograde injection of kallikrein through the ureter into the collecting duct system of barbiturate‐anaesthetized rats was lower than that from kidneys administered the vehicle (experiment 4; P < 0.001). A retrograde injection of bradykinin was without effect (experiment 5). 6. We conclude that renal kallikrein is involved in the regulation of urinary bicarbonate excretion. Increased intraluminal activity of the enzyme reduces, and decreased kallikrein activity increases, bicarbonate excretion. The enzyme may be a component of a negative feedback loop controlling the hydrogen ion activity of the extracellular space.
Characterization of an ATP‐modulated large conductance Ca(2+)‐activated K+ channel present in rat cortical neurones.
Authors: Lee K , Rowe I C , Ashford M L
Published: December 2014

1. Single channel current recordings were used to study the characteristics of a large conductance Ca(2+)‐activated K+ (BKCa) channel present in neurones acutely dissociated from the rat motor cortex. Application of ATP to the intracellular surface of excised inside‐out patches produced a large, concentration‐dependent increase in BKCa channel activity. 2. This ATP‐mediated activation was dependent upon the presence of Mg2+ in the intracellular bathing solution and was diminished by the phosphatases 2,3‐butanedione monoxime (BDM) or alkaline phosphatase and by the protein kinase inhibitors staurosporine, H‐7 and PKI. 3. ADP stimulated BKCa channel activity in a Mg(2+)‐dependent manner, an action also inhibited by the concomitant application of PKI or BDM. The effect of ADP was reduced by application of hexokinase and glucose or by application of the adenylate kinase inhibitor Ap5A. 4. Of other nucleotides tested, only CTP consistently activated BKCa channel activity. 5. Using the cell‐attached configuration, bath application of forskolin or dibutyryl cAMP stimulated BKCa channel activity. 6. It is concluded that BKCa channel activity in the rat motor cortex is subject to modulation by the activity of a closely associated kinase. The ability of cAMP activators to stimulate BKCa channel activity in the intact cell suggests that this system may be of physiological importance.
Expression of immediate early genes in rat gastric myenteric neurones: a physiological response to feeding.
Authors: Dimaline R , Miller S M , Evans D , Noble P J , Brown P , Poat J A
Published: December 2014

1. Expression of the immediate early genes c‐fos, c‐jun and c‐myc in rat stomach in response to feeding and gastric distension was examined by Northern blot analysis and in situ hybridization. 2. Refeeding of fasted rats induced a transient increase in c‐fos mRNA abundance in gastric corpus and antrum that was sixfold within 15 min and declined within 4 h. The response was not mediated by gastrinergic or muscarinic cholinergic mechanisms; it was reduced but not abolished by hexamethonium. No changes in expression of c‐jun, c‐myc or the constitutively expressed protein glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) were observed. 3. In conscious rats prepared with a gastric fistula, gastric distension with nutritive and non‐nutritive solutions at a physiological pressure for 30 min induced expression of c‐fos, c‐jun and c‐myc, but not GAPDH. 4. Messenger RNA encoding c‐fos was localized by in situ hybridization to gastric myenteric neurones of animals that underwent gastric distension, but not of undistended controls. 5. The results suggest that expression of c‐fos in gastric myenteric neurones is an early response to the physiological stretching of the stomach wall that accompanies feeding. With supraphysiological distension, other immediate early genes may be recruited.
Voltage‐gated potassium currents in stratum oriens‐alveus inhibitory neurones of the rat CA1 hippocampus.
Authors: Zhang L , McBain C J
Published: December 2014

1. Voltage‐activated K+ currents were recorded from visually identified inhibitory interneurones of the CA1 stratum oriens‐alveus region in neonatal rat hippocampal slices using outside‐out patch and whole‐cell voltage clamp techniques. 2. Outward currents comprised both a transient and a sustained component when elicited from a holding potential of ‐90 mV. Tail current analysis of current reversal potentials showed that outward currents were carried by potassium ions. 3. The transient current, IA, was activated with a time to peak within 5 ms, inactivated with a time constant of approximately 15 ms at 0 mV and possessed half‐activation at ‐14 mV. Half‐inactivation of the transient current occurred at ‐71 mV. At ‐90 mV, the transient current recovered from inactivation with a time constant of 142 ms. 4. Activation of currents from a holding potential of ‐50 mV permitted isolation of the sustained current, IK. In Ca(2+)‐free conditions the sustained current showed rapid activation, reaching about 80% of its maximum within 1.5 ms, and showed little inactivation during 1 s depolarizing steps. The majority of sustained outward currents showed no voltage‐dependent inactivation. In approximately 20% of cells, a slow time‐dependent inactivation of the sustained current was observed, suggesting the presence of a second type of sustained current in these cells. 5. A Ca(2+)‐dependent K+ current comprised a significant portion of the total sustained current; this current was activated at voltages positive to ‐30 mV and showed no time‐dependent inactivation over a 1 s depolarizing step. This current component was removed in Ca(2+)‐free conditions or by iberiotoxin. 6. Low concentrations of 4‐AP (50 microM) attenuated both the transient and sustained current components recorded in a Ca(2+)‐free solution. Higher concentrations of 4‐AP (< 10 mM) were without further effect on the sustained current but completely blocked the transient current with an IC50 of 1.8 mM. TEA blocked the sustained current with an IC50 of 7.9 mM without significantly reducing the transient current. Both current components were resistant to dendrotoxin (500 nM).
Regional difference in the distribution of L‐NAME‐sensitive and ‐insensitive NANC relaxations in cat airway.
Authors: Takahashi N , Tanaka H , Abdullah N , Jing L , Inoue R , Ito Y
Published: December 2014

1. To investigate the distribution profile of functional inhibitory non‐adrenergic non‐cholinergic (i‐NANC) nerves and the contribution of NO to the NANC relaxation in the cat, we studied the effects of N omega‐nitro‐L‐arginine methyl ester (L‐NAME) on NANC relaxation elicited by electrical field stimulation (EFS) in the trachea, bronchus and bronchiole. 2. EFS applied to the tracheal smooth muscle during contraction induced by 5‐HT (10(‐5) M) in the presence of atropine (10(‐6) M) and guanethidine (10(‐6) M) elicited a monophasic NANC relaxation. By contrast, NANC relaxation elicited in the peripheral airway was biphasic, comprising an initial fast followed by a second slow component and L‐NAME (10(‐5) M) selectively abolished the first component without affecting the second one. In the trachea, L‐NAME (10(‐5) M) completely suppressed the monophasic NANC relaxation when single or short repetitive stimuli (< 5) with 1 ms pulse duration were applied. However, at higher repetitive stimuli (> 10) with 1 or 4 ms pulse duration, suppression of NANC relaxation was incomplete. 3. In the small bronchi obtained from L‐NAME‐pretreated cats, EFS applied during contraction induced by 5‐HT (10(‐5) M) elicited only the slow component of NANC relaxation which is sensitive to tetrodotoxin. 4. In the peripheral airway, a newly synthesized VIP antagonist (10(‐6) M) or alpha‐chymotrypsin (1 U ml‐1) considerably attenuated the amplitude of L‐NAME‐insensitive relaxation. 5. Single or repetitive EFS consistently evoked excitatory junction potentials (EJPs) in the central and peripheral airways. When tissues were exposed to atropine (10(‐6) M) and guanethidine (10(‐6) M), single or repetitive EFS did not alter the resting membrane potential. 6. These results indicate that at least two neurotransmitters, possibly NO or NO‐containing compounds and VIP, are involved in i‐NANC neurotransmission and the distribution profile of the two components differs in the central and peripheral airway of the cat.
Task‐related variation in corticospinal output evoked by transcranial magnetic stimulation in the macaque monkey.
Authors: Baker S N , Olivier E , Lemon R N
Published: December 2014

1. A volley evoked by transcranial magnetic stimulation (TMS) over the motor cortex was recorded from the medullary pyramid in an awake monkey performing a precision grip task. It was identified as corticospinal using a collision test. 2. The volley latency was 0.50 ms, indicating that it was produced by direct activation of corticospinal neurones. 3. A mean modulation of 13% in the amplitude of this volley was seen during task performance, with the largest volley occurring during the hold phase of the task. A similar pattern of modulation was seen in the EMG responses of hand and forearm muscles to TMS. 4. No comparable modulation was observed in a volley evoked by electrical stimulation of the corticospinal fibres via chronically implanted electrodes in the cerebral peduncle. 5. The results are compatible with direct activation of the corticospinal neurones by TMS at a site close to the soma, with the probability of activation by TMS depending on the current level of cortical excitability.
Inhibition of ACh release at an Aplysia synapse by neurotoxic phospholipases A2: specific receptors and mechanisms of action.
Authors: Fossier P , Lambeau G , Lazdunski M , Baux G
Published: December 2014

1. Monochain (OS2) and multichain (taipoxin) neurotoxic phospholipases A2 (PLA2), purified from taipan snake venom, both inhibited ACh release at a concentration of 20 nM (90% inhibition in 2 h) at an identified synapse from buccal ganglion of Aplysia californica. 2. The Na+ current was unchanged upon application of either OS2 or taipoxin. Conversely, presynaptic K+ currents (IA and IK) were increased by taipoxin but not by OS2. In addition, OS2 induced a significant decrease of the presynaptic Ca2+ current (30%) while taipoxin increased this latter current by 20‐30%. 3. Bee venom PLA2, another monochain neurotoxic PLA2, also inhibited ACh release while non‐toxic enzymatically active PLA2s like OS1 (also purified from taipan snake venom) or porcine pancreatic PLA2 elicited a much weaker inhibition of ACh release, suggesting a specific action of neurotoxic PLA2s versus non‐toxic PLA2s on ACh release. 4. Using iodinated OS2, specific high affinity binding sites with molecular masses of 140 and 18 kDa have been identified on Aplysia ganglia. The maximal binding capacities were 55 and 300‐400 fmol (mg protein)‐1 for membrane preparations from whole and buccal ganglia, respectively. These binding sites are of high affinity for neurotoxic PLA2s (Kd values, 100‐800 pM) and of very low affinity for non‐toxic PLA2s (Kd values in the micromolar range), thus indicating that these binding sites are presumably involved in the blockade of ACh release by neurotoxic PLA2s.
Cellular mechanisms of 4‐aminopyridine‐induced synchronized after‐discharges in the rat hippocampal slice.
Authors: Traub R D , Colling S B , Jefferys J G
Published: December 2014

1. We constructed a model of the in vitro rodent CA3 region with 128 pyramidal neurones and twenty‐four inhibitory neurones. The model was used to analyse synchronized firing induced in the rat hippocampal slice by 4‐aminopyridine (4‐AP), a problem simultaneously studied in experiments in rat hippocampal slices. N‐methyl‐D‐aspartate (NMDA) receptors were blocked. 2. Consistent with a known action of 4‐AP, unitary EPSCs were assumed to be large and prolonged. With augmented EPSCs, spontaneous synchronized bursts occurred in the model if random ectopic axonal spikes were present. We observed probable antidromic spikes and miniature spikes experimentally. 3. Consistent with experiment, model synchronized bursts were preceded by a period of about 100 ms of increased unit activity and cell depolarization. In the model, this was caused in part by EPSPs consequent to ectopic axonal spikes. 4. After widespread firing had begun, full‐blown synchrony in the model required orthodromic EPSPs. A single synchronized burst, once initiated, could proceed without further ectopic activity. 5. A depolarizing change in reversal potential for dendritic GABAA favoured the occurrence of synchronized after‐discharges in the model. Consistent with this, bicuculline was found to block after‐discharges in slices bathed in 4‐AP (70 microM) during NMDA blockade. 6. These data indicate that, even with synaptic inhibition present, ectopic spikes can ‘set the stage’ for synchronized activity by depolarizing pyramidal cell dendrites, but that recurrent orthodromic EPSPs are required for expression of this synchrony. When synaptic inhibition is present, EPSCs may need to be larger than usual for synchrony to take place. Secondary bursts in 4‐AP appear to be driven in part by a depolarizing GABAA‐mediated current.
Increase in reciprocal Ia inhibition during antagonist contraction in the human leg: a study of motor units and the H reflex.
Authors: Shindo M , Yanagawa S , Morita H , Yanagisawa N
Published: December 2014

1. The change in reciprocal Ia inhibition of soleus motoneurones produced by stimulation of the common peroneal nerve was investigated by the use of twenty‐three soleus motor units as well as the soleus H reflex in six normal subjects during tonic pretibial contraction. 2. In the motor unit experiments, motoneuronal excitability was measured as the ‘critical firing stimulus’ (CFS), which is the difference between the test stimulus intensity needed to reach the threshold for the lowest threshold Ia fibres and the intensity which evokes firing of a motor unit with the probability of 50%. The conditioning effect, assessed from the change in the CFS, was expressed as a percentage of the unconditioned CFS. 3. At a conditioning intensity of 0.95 times the motor threshold value, there was Ia inhibition in sixteen of the twenty‐three motor units (69.6%) at rest. Of these sixteen motor units, twelve showed increases in inhibition at intervals below 2.0 ms during pretibial contraction. In four of the remaining seven units, inhibition first appeared during contraction. There was no significant decrease in inhibition at any time during contraction. 4. Based on the conventional H reflex, reciprocal Ia inhibition increased during very weak (below 2% of the maximum) voluntary dorsiflexion and continued to increase at a slightly stronger (3‐8% of the maximum) contraction, then decreased continuously when contraction was strengthened further. Maximal inhibition occurred at a relatively strong contraction when a weak conditioning stimulus was used, and vice versa. 5. We conclude that the activity of reciprocal Ia inhibitory interneurones increases during tonic antagonist contraction. The previous controversy about this inhibition is the result of occlusion at the Ia interneuronal level.
Cytosolic calcium concentration in resting and stimulated endothelium of excised intact rat aorta.
Authors: Usachev Y M , Marchenko S M , Sage S O
Published: December 2014

1. Optical fibres were used to excite and record fluorescence from the lumenal face of rat aorta or tail artery loaded with fura‐2. 2. Acetylcholine (ACh) evoked an endothelium‐dependent rise in the fura‐2 340/380 nm excitation ratio in both vessels. High [K+] or phenylephrine evoked an endothelium‐independent rise in ratio in tail artery but failed to increase the ratio in aorta. These observations indicate that fura‐2 fluorescence and therefore cytosolic calcium concentration ([Ca2+]i) may be selectively recorded from the endothelium of intact rat aorta. 3. In aortic endothelium, resting [Ca2+]i was 95 +/‐ 8 nM (n = 44). ACh evoked a monophasic rise in [Ca2+]i which was temporally coincident with a membrane hyperpolarization. 4. ATP in most (22/35) preparations evoked a rise in [Ca2+]i which declined towards resting and was followed by a secondary rise. The biphasic [Ca2+]i responses were accompanied by biphasic electrical responses of initial hyperpolarization followed by depolarization above the resting potential and subsequent restoration towards rest. In the presence of high [K+] or the K+ ionophore valinomycin, ATP did not evoke changes in membrane potential and only monophasic rises in [Ca2+]i were observed. In some (7/35) preparations, ATP evoked oscillations in [Ca2+]i, with membrane potential oscillating in antiphase. 5. These data suggest interplay between [Ca2+]i and membrane potential in the generation of agonist‐evoked responses in native endothelium in situ. The observed oscillations in [Ca2+]i imply spatio‐temporal synchronization of Ca2+ signalling in large groups of endothelial cells in intact rat aorta.
Excitability changes of somatic and viscero‐somatic nociceptive reflexes in the decerebrate‐spinal rabbit: role of NMDA receptors.
Authors: Laird J M , de la Rubia P G , Cervero F
Published: December 2014

1. Wind‐up (frequency‐dependent potentiation of the responses of spinal neurones to stimulation of unmyelinated afferents) and other N‐methyl‐D‐aspartate (NMDA) receptor‐mediated phenomena have been proposed as key mechanisms underlying persistent pain states. In this study we have compared wind‐up in visceral and somatic nociceptive pathways to examine the possible contribution of these mechanisms to visceral pain and hyperalgesia. 2. Experiments were performed on thirteen decerebrate spinalized rabbits. A somato‐somatic (SS) reflex (evoked by stimulating skin and muscle afferents from the L2 spinal nerve) and a viscero‐somatic (VS) reflex (evoked by stimulating visceral afferents in the splanchnic nerve) were recorded from the L1 spinal nerve. The reflexes consisted of an early (A fibre) and a late (C fibre) component. 3. Conditioning trains of sixteen high intensity electrical stimuli at 1 Hz were applied to the somatic or visceral nerve. These conditioning stimuli did not produce wind‐up in the early component of either reflex but evoked powerful wind‐up in the late SS reflex (mean percentage of baseline +/‐ S.E.M., 191 +/‐ 30%). In contrast wind‐up was weak or absent in the late VS reflex (mean percentage of baseline +/‐ S.E.M., 21 +/‐ 6%). Conditioning of somatic afferents facilitated both the early and late SS reflex but strongly depressed the early and late VS reflex. Conditioning of visceral afferents had little effect on the early SS reflex, but depressed the early VS reflex and the late components of both reflexes. 4. Intravenous administration (1‐10 mg kg‐1) of the NMDA receptor antagonist ketamine dose‐dependently inhibited the strong wind‐up in the late SS reflex and the weak wind‐up in the late VS reflex, but also dose‐dependently inhibited the early and late components of both baseline reflexes. 5. We conclude that neural mechanisms other than wind‐up may underlie the development of visceral pain and hyperalgesia. The present results emphasize the important differences in the processing of somatic and visceral nociceptive input by spinal nociceptive systems and confirm the involvement of NMDA receptors in the spinal processing of nociceptive information.
Modulation of glomus cell membrane currents of intact rat carotid body.
Authors: Donnelly D F
Published: December 2014

1. In order to understand better the relationship between sinus nerve chemoreceptor activity and changes in glomus cell membrane current, both were measured simultaneously in rat carotid bodies in vitro. Mean membrane resistance of intact glomus cells was 1327 +/‐ 140 M omega (n = 104, mean +/‐ S.E.M.) and membrane capacitance was 7.9 +/‐ 0.8 pF (n = 28). 2. Over the course of 15 min following the start of whole‐cell recording, outward current increased by 169 +/‐ 48% (n = 19), but there was no significant change in holding current or membrane resistance. Reversal potential of the tail current was not changed over this time period. Current run‐up was not affected by addition of ATP, Ca2+, okadaic acid or H‐7 to the pipette fluid. 3. Brief hypoxia (30‐45 s duration, 0 mmHg at nadir) caused a rapid increase in nerve activity, but, on average, no significant change in cell holding current, or resistance. Outward current slightly decreased during hypoxia but failed to recover in the post‐hypoxia period. 4. Tetraethylammonium (20 mM), and 4‐aminopyridine (1 mM) reduced the outward current to 54 +/‐ 7 and 66 +/‐ 3% of control, respectively, but basal nerve activity was unchanged and the nerve response to hypoxia remained intact. 5. These results suggest that hypoxia modulation of glomus cell K+ current is not the primary initiating factor in the nerve response to brief periods of hypoxia in the rat carotid body.
Synthesis and release of an acetylcholine‐like compound by human myoblasts and myotubes.
Authors: Hamann M , Chamoin M C , Portalier P , Bernheim L , Baroffio A , Widmer H , Bader C R , Ternaux J P
Published: December 2014

1. Exogenously applied acetylcholine (ACh) is a modulator of human myoblast fusion. Using a chemiluminescent method, we examined whether an endogenous ACh‐like compound (ACh‐lc) was present in, and released by, pure human myogenic cells. 2. Single, freshly isolated satellite cells and proliferating myoblasts contained 15 and 0.5 fmol ACh‐lc, respectively. Cultured myotubes contained ACh‐lc as well. Also, ACh‐like immunoreactivity was detected in all myogenic cells. 3. Part of the ACh‐lc was synthesized by choline acetyltransferase (ChAT), as indicated by the reduction of ACh‐lc content when bromoACh was present in the culture medium, and by direct measurements of ChAT activity. Also, ChAT‐like immunoreactivity was observed in all myogenic cells. 4. Myoblasts and myotubes released ACh‐lc spontaneously by a partially Ca(2+)‐dependent mechanism. 5. The application by microperfusion of medium conditioned beforehand by myoblasts (thus presumably containing ACh‐lc) onto a voltage‐clamped myotube induced inward currents resembling ACh‐induced currents in their kinetics, reversal potential, and sensitivity to nicotinic antagonists. 6. In vitro, the spontaneously released ACh‐lc promoted myoblast fusion but only in the presence of an anticholinesterase. 7. Our observations indicate that human myogenic cells synthesize and release an ACh‐lc and thereby promote the fusion process that occurs in muscle during growth or regeneration.