bluuebunny/crossref_metadata_2025 huggingface dataset:
Two calcium‐activated chloride conductances in Xenopus laevis oocytes permeabilized with the ionophore A23187.
Authors: Boton R , Dascal N , Gillo B , Lass Y
Published: December 2014

1. Currents evoked by elevated intracellular free Ca2+ in Xenopus laevis oocytes were studied using the two‐electrode voltage clamp technique. The elevation in Ca2+ concentration was achieved in three ways: by the use of the divalent cation ionophore A23187; by application of Ca2+‐mobilizing neurotransmitters serotonin and acetylcholine (ACh); by the entry of Ca2+ through voltage‐dependent channels. 2. In most experiments, the membrane was permeabilized to Ca2+ by a 15 min pretreatment with A23187 in a Ca2+‐free solution. Exposure of the ionophore‐treated oocytes to external Ca2+ elicited an inward current (at holding potentials of ‐40 to ‐60 mV). At external Ca2+ concentrations ([Ca2+]) between 0.1 and 1 mM, the current had a time‐to‐peak of at least 10 s, and slowly decayed over tens of seconds. At [Ca2+] greater than 2 mM, the inward current had two distinct kinetic components, a fast and transient one (Ifast) and a slow one (Islow). 3. The main carrier of the Ca2+‐evoked inward current was Cl‐. Several data indicate the existence of a tetraethylammonium (TEA)‐sensitive K+ conductance. No evidence for a Na+ current was found. 4. The two components of the Ca2+‐evoked inward current in ionophore‐permeabilized oocytes, and the two components of the current evoked by ACh and serotonin (the latter in oocytes injected with rat brain RNA but untreated with A23187), were blocked by intracellular injection of the Ca2+ chelator, ethyleneglycolbis‐(beta‐aminoethyl ether)‐N,N,N'N'‐tetraacetic acid (EGTA). The two components of these currents displayed different sensitivity to Ca2+ buffering; higher doses of EGTA were necessary to inhibit the slow component than the fast one. 5. One to two minutes of treatment with 2 mM‐9‐anthracene carboxylic acid (9‐AC) fully blocked Ca2+‐dependent Cl‐ current evoked by Ca2+ influx through voltage‐ dependent Ca2+ channels in intact (untreated with A23187) oocytes. In ionophore‐treated oocytes, block of Ifast was observed at holding potentials at which the current was outward (i.e. due to Cl‐ influx); Islow was inhibited only partially. The block of Ca2+‐evoked Cl‐ efflux by 9‐AC developed much more slowly and was less potent. to explain these results, the existence of two sites of 9‐AC action is proposed. 6. Exposure of the ionophore‐permeabilized oocytes to 0.1‐0.2 mM [Ca2+] strongly reduced the response to higher concentrations of Ca2+. Ifast displayed stronger Ca2+‐dependent inactivation than Islow.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of intracellular ruthenium red on excitation‐contraction coupling in intact frog skeletal muscle fibres.
Authors: Baylor S M , Hollingworth S , Marshall M W
Published: December 2014

1. Ruthenium Red (RR) blocks sarcoplasmic reticulum (SR) Ca2+ release in disrupted muscle preparations and this block has been used as a marker for the physiological Ca2+ release pathway. To investigate whether RR can also affect SR Ca2+ release in living muscle, optical signals reflecting Ca2+ release have been measured in intact single frog twitch fibres microinjected with RR. 2. The total myoplasmic concentration of RR, [RRT], was obtained from measurements of RR‐related absorbance and apparent diffusion constant, Dapp, of RR in myoplasm was estimated. The value of Dapp was about 1/30 of that expected and can be explained if the majority of RR (approximately 97%) was bound in myoplasm and free [RR] was only 1/30 of [RRT]. 3. Sarcoplasmic reticulum Ca2+ release following action potential stimulation was assessed from a Ca2+‐related change in intrinsic birefringence. The birefringence signal was blocked in the presence of RR and the degree of block was clearly dependent upon [RRT]. At 16 degrees C the estimated [RRT] for half‐block of the birefringence signal was 23 +/‐ 4 microM (+/‐ S.E. of mean; n = 3), and for half‐block of the Ca2+ release process itself was 72 +/‐ 14 microM. The estimated free [RR] for half‐block is then 0.8 +/‐ 0.1 and 2.4 +/‐ 0.5 microM, respectively. In the cold (6‐8 degrees C), the half‐blocking concentration of RR, referred to [RRT], appeared to be about 3‐fold smaller than that observed at 16 degrees C. 4. The values estimated for the free [RR] which caused half‐block of Ca2+ release in intact muscle fibres are in the range reported for RR's action in disrupted preparations, thus supporting the conclusion that the RR‐blockable channel observed in disrupted muscle is the physiologically important Ca2+ release channel. 5. Intramembrane charge movements in skeletal muscle are thought to underlie the dependence of SR Ca2+ release on transverse tubular membrane potential. Charge movements were measured in RR‐injected fibres at 4‐6 degrees C using a three‐microelectrode, middle‐of‐the‐fibre voltage‐clamp technique. Injected fibres did not survive well in solutions made hypertonic to prevent fibre movement and allow measurement of suprathreshold charge; therefore charge movements below contraction threshold were studied in isotonic solution.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of the block of single Na+ channels in guinea‐pig ventricular myocytes by the local anaesthetic penticainide.
Authors: Carmeliet E , Nilius B , Vereecke J
Published: December 2014

1. The blocking mechanism of a disopyramide derivative Penticainide (2‐alkyl‐(4‐(dialkylamino)‐2‐)pyridyl‐butyramide) on cardiac Na+ channels has been studied using single‐channel analysis in cell‐attached and inside‐out patches from guinea‐pig ventricular cells. Penticainide was applied in concentrations between 3 and 100 microM. The S‐enantiomer of DPI 201‐106 (5 microM) was used as a tool to slow the inactivation, improve the time resolution by prolonging the mean open time, and to increase the number of openings per depolarization of the channel. 2. When in cell‐attached or inside‐out patch experiments up to 100 microM‐Penticainide was applied to the bathing solution no significant effect was observed on the probability of the channel being open or on the mean open time. 3. In cell‐attached patch experiments with 100 microM‐Penticainide in the pipette, the open‐state probability of the Na+ channel was much lower than in the absence of Penticainide. No significant changes were found in the potential of half‐maximum activation or in the slope of the activation curve. The maximum open‐state probability was reduced by a factor five in the presence of Penticainide. The single‐channel conductance was not affected by the drug. 4. The decrease in the probability of the channel being open was mainly due to an increased probability of observing sweeps with no activity ('nulls'). 5. A dramatic relief from the block was observed when pauses were interposed into the normal activation pattern, or when the pacing rate was reduced. 6. The distribution of the open times of the bursting Na+ channel could be fitted with two exponentials. Penticainide in the patch pipette reduced the mean open time. Also the contribution of the number of long openings to the total number of openings was reduced. 7. Closed‐time distribution was also fitted with two exponentials. Penticainide in the patch pipette prolonged the long mean closed time. The contribution of the number of short closings to the total number of closings was decreased. 8. Penticainide in the patch pipette did not significantly change the time constant of the decay of the ensemble‐averaged currents measured at ‐30 mV. Because of the close correlation between the burst duration and the time constant of inactivation (Nilius, Vereecke & Carmeliet, 1988b), we conclude that no striking effect of Penticainide on the burst duration can be expected.(ABSTRACT TRUNCATED AT 400 WORDS)
Distribution of mesencephalic nucleus and trigeminal ganglion mechanoreceptors in the periodontal ligament of the cat.
Authors: Linden R W , Scott B J
Published: December 2014

1. In anaesthetized cats recordings have been made in the mesencephalic nucleus of the fifth cranial nerve and the trigeminal ganglion from neurones that respond when forces are applied to the mandibular canine tooth. The site of the mechanoreceptors in the periodontal ligament and their distribution around the tooth root have been determined. 2. Receptors with their cell bodies in the mesencephalic nucleus were found to be situated in the periodontal ligament in a discrete area intermediate between the fulcrum and apex of the tooth, while those in the trigeminal ganglion were situated in the whole area of the periodontal ligament between the fulcrum and apex of the tooth. 3. All of the located mechanoreceptors responded maximally when that part of the ligament in which they lay was put under tension. 4. The directional sensitivities of the mechanoreceptors suggested that there was an uneven distribution around the tooth root of receptors with cell bodies in the mesencephalic nucleus. In contrast mechanoreceptors with cell bodies in the trigeminal ganglion were distributed more equally around the tooth root. The rationale for the differences requires further investigation.
A comparison of head‐down tilt with low‐dose infusion of atrial natriuretic peptide in man.
Authors: Allen M J , Ang V T , Bennett D
Published: December 2014

1. Procedures that increase atrial pressure, such as head‐down tilt, result in an increase in plasma atrial natriuretic peptide (ANP) and a natriuresis, but a direct cause‐and‐effect relationship between these two responses has not been established. This study was undertaken to compare the effects of head‐down tilt with exogenous ANP on renal function. 2. Eight normal sodium‐replete volunteers underwent a 3 h placebo infusion, a 3 h ANP infusion at 1.2 pmol kg‐1 min‐1 and a 3 h period of head‐down tilt. Each procedure was performed on a separate day, in random order. 3. ANP and head‐down tilt produced similar increases in sodium excretion (65 +/‐ 24 and 68 +/‐ 16%, respectively). ANP did not increase urine flow significantly more than placebo. Head‐down tilt increased urine flow significantly more than placebo and ANP. 4. Plasma ANP rose from 8.1 +/‐ 1.0 to 11.4 +/‐ 2.5 pg ml‐1 during head‐down tilt and from 6.5 +/‐ 1.4 to 32.3 +/‐ 10.7 pg ml‐1 with ANP infusion. 5. ANP infusion had no significant effects on systemic haemodynamics whilst head‐down tilt increased cardiac output and reduced heart rate and an index of systemic vascular resistance. 6. ANP infusion, whilst achieving a natriuretic response similar to that of tilt, was associated with a 3‐fold higher mean plasma ANP level. Although plasma ANP rose during both ANP infusion and tilt, there was a lack of correlation between natriuretic response and plasma ANP. 7. The results are not compatible with a direct cause‐and‐effect relationship between plasma ANP and sodium excretion during head‐down tilt.
Dissociation of force from myofibrillar MgATPase and stiffness at short sarcomere lengths in rat and toad skeletal muscle.
Authors: Stephenson D G , Stewart A W , Wilson G J
Published: December 2014

1. Single fast‐twitch fibres from the extensor digitorum longus muscle of the rat, Rattus norvegicus, and single twitch fibres from the iliofibularis muscle of the cane toad, Bufo marinus, were mechanically skinned and then used to measure maximally Ca2+‐activated [( Ca2+] greater than 0.03 mmol l‐1) isometric force production, myofibrillar MgATPase activity and fibre stiffness at different sarcomere lengths. MgATP hydrolysis was linked by an enzyme cascade to the oxidation of NADH (nicotinamide adenine dinucleotide, reduced form) and was monitored by a microfluorimetric system. Fibre stiffness was measured from the amplitude of force oscillations generated by small sinusoidal length changes. 2. At sarcomere lengths which were optimal for isometric force production (around 2.7 microns for rat and 2.2 microns for toad fibres) the myofibrillar MgATPase activity (mean +/‐ S.E.M.) at 21‐22 degrees C was found to be 3.80 +/‐ 0.53 molecules MgATP hydrolysed s‐1 per myosin head for eight rat fibres and 6.35 +/‐ 0.77 s‐1 per myosin head for four toad fibres. 3. At sarcomere lengths shorter than 2.7 microns in rat fibres and 2.2 microns in toad fibres, MgATPase and stiffness remained elevated and close to their respective values at 2.7 microns in rat fibres and 2.2 microns in toad fibres even when the isometric force decreased to near zero levels. 4. The dissociation at short sarcomere lengths of myofibrillar MgATPase activity and fibre stiffness from isometric force suggests that the cross‐bridge cycle is not greatly affected by double actin filament overlap with the myosin filaments at short sarcomere lengths. Moreover, the results suggest that cross‐bridges can be formed by myosin with actin filaments projecting from the nearest Z‐line and from the Z‐line in the other half of the sarcomere. 5. These results help to reconcile energetic and mechanical data obtained by others at short sarcomere lengths and can be explained within the framework of the sliding filament theory.
Effects of corticosteroid hormones on the electrophysiology of rat distal colon: implications for Na+ and K+ transport.
Authors: Binder H J , McGlone F , Sandle G I
Published: December 2014

1. Conventional microelectrodes, the Na+ channel blocker amiloride (0.1 mM), and the K+ channel blocker tetraethylammonium chloride (TEA, 30 mM) were used to examine the effects of corticosteroid hormones administered in vivo on the Na+ and K+ transport properties of isolated rat distal colon. The cell membrane changes induced by aldosterone (a specific mineralocorticoid), RU 28362 (a synthetic glucocorticoid with negligible affinity for mineralocorticoid receptors), and dexamethasone (an activator of both mineralocorticoid and glucocorticoid receptors) were compared. 2. In control animals, there was no amiloride‐sensitive apical Na+ conductance, and only a relatively small TEA‐sensitive apical K+ conductance. 3. Hyperaldosteronism secondary to dietary Na+ depletion for 10‐14 days, dexamethasone (600 micrograms 100 g‐1 day‐1 for 3 days), and RU 28362 (600 micrograms 100 g‐1 day‐1 for 3 days) induced amiloride‐sensitive electrogenic Na+ transport, with the potency of aldosterone greater than dexamethasone greater than RU 28362. 4. With each corticosteroid, increased electrogenic Na+ transport reflected enhanced apical Na+ conductance, and in the case of aldosterone and dexamethasone, 3.3‐fold and 2‐fold increases respectively in the maximum activity of the basolateral Na+‐K+ pump. In contrast, RU 28362 suppressed the maximum activity of the basolateral Na+‐K+ pump by 45%. 5. All three corticosteroids enhanced the K+ conductance of the apical membrane, with the potency of aldosterone greater than dexamethasone greater than RU 28362. 6. Co‐administration of spironolactone (5 mg 100 g‐1 day‐1) inhibited the effects of aldosterone on Na+ and K+ transport, but in dexamethasone‐treated animals spironolactone resulted in a pattern of response similar to that found in RU 28362‐treated animals. 7. The results support the view that mineralocorticoid receptors mediate changes in colonic Na+ and K+ transport which differ quantitatively and qualitatively from those mediated by glucocorticoid receptors. Dexamethasone and similar ‘glucocorticoids’ activate both types of receptor, with an overall epithelial response which mimics that induced by aldosterone.
Adjacent interval analysis distinguishes among gating mechanisms for the fast chloride channel from rat skeletal muscle.
Authors: Blatz A L , Magleby K L
Published: December 2014

1. The durations of adjacent open and shut intervals, obtained with the patch‐clamp technique from fast Cl‐ channels in tissue‐cultured rat skeletal muscle, were analysed to distinguish among eight previously considered gating mechanisms for the channel which differed in the connections among the states. 2. Open intervals were separated into groups based on the duration of the shut intervals which occurred before or after each open interval. Fitting these conditional open distributions with sums of exponentials indicated that they were described by two exponential components. 3. The time constants of the two components in the conditional open distributions were independent of the adjacent shut interval durations. The observation of invariant time constants is consistent with gating mechanisms in which the rate constants for transitions among the states remain constant with time (discrete Markov process). 4. In contrast to the invariant time constants, the areas of the two components in the conditional open distributions were dependent on the adjacent shut interval durations. The area of the fast open component increased, and the area of the slow open component decreased, as the duration of adjacent shut intervals increased. Thus, it is changes in areas, rather than time constants, which give rise to the observed inverse relationship between the durations of adjacent open and shut intervals. 5. The findings in summary statements 2‐4 indicate that at least two open states are connected by independent pathways to different shut states; the open state associated with the fast open component is connected to a shut state (or compound shut state) of longer effective lifetime, and the open state associated with the slow open component is connected to a shut state (or compound shut state) of briefer effective lifetime. 6. Seven of the eight previously considered gating mechanisms were rejected because they did not account for the observed relationships between the durations of adjacent open and shut intervals, when analysed in terms of either conditional open distributions or conditional mean open interval durations. 7. The seven rejected gating mechanisms also did not account for the observed correlations between interval durations, when analysed in terms of correlation coefficients. Adjacent interval and correlation analysis thus provided a means to distinguish among the gating mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of peripheral and central chemoreflex activation on the isopnoeic rating of breathing in exercising humans.
Authors: Ward S A , Whipp B J
Published: December 2014

1. Respiratory sensation during exercise is generally considered to be related to respiratory mechanical factors which may be manifest as an abnormal relationship between the force applied to the lungs and chest wall and the resulting motion (if any); that is, a ‘length‐tension’ inappropriateness (Campbell & Howell, 1963). This suggests that there should be a direct correlation between ventilation (VE) and the associated intensity of the perceived sensation, such that the sensation associated with a particular level of VE should remain essentially constant regardless of the source of respiratory stimulation. 2. In order to establish whether certain respiratory stimuli might be ‘dyspnoeagenic’ (i.e. capable of evoking an intensity of respiratory sensation out of proportion to their influence on VE), we investigated the influence of both peripheral chemoreflex activation (induced by isocapnic hypoxia) and central chemoreflex activation (induced by hypercapnic hyperoxia) on the intensity of respiratory sensation in seven healthy adults during moderate cycle ergometer exercise (i.e. below the lactate threshold, theta 1ac). 3. In each test, an ‘isopnoea’ was established for which a particular level of VE was sustained over a prolonged period (approximately 30 min) while the proportional contributions to the ventilatory drive from either exercise and the peripheral chemoreflex or from exercise and the central chemoreflex were slowly altered to new stable levels, without the subject's knowledge, VE, tidal volume, inspiratory and expiratory durations, mean inspiratory flow, and end‐tidal PCO2 and PO2 (PET,CO2, PET,O2) were monitored breath‐by‐breath. The intensity of respiratory sensation was rated with a visual analogue scale. 4. Isopnoeic ratings of respiratory sensation were systematically greater for peripheral chemoreflex activation by isocapnic hypoxia during exercise at 50% theta 1ac (for which the degree of peripheral chemoreflex activation, estimated by hyperoxic transition or ‘Dejours’ testing, averaged approximately 23% of the total VE), compared to 90% theta 1ac during isocapnic hyperoxia. Ratings during exercise at 50% theta 1ac for central chemoreflex activation by hypercapnic hyperoxia were not systematically different from 90% theta 1ac during isocapnic hyperoxia, however. 5. As VE was stable throughout each isopnoea and the MVV (maximum voluntary ventilation) was uninfluenced by the test condition, the dyspnoea index (VE x 100/MVV) was not affected. Breathing pattern was also unaffected. 6. We conclude that in normal subjects exercising moderately, activation of the peripheral chemoreceptors by isocapnic hypoxia evokes an intensity of respiratory sensation which is out of proportion to that evoked by an isopnoeic stimulation of the central chemoreceptors with hypercapnic hyperoxia at the same level of exercise.(ABSTRACT TRUNCATED AT 400 WORDS)
The human pressor response during and following voluntary and evoked isometric contraction with occluded local blood supply.
Authors: Bull R K , Davies C T , Lind A R , White M J
Published: December 2014

1. Changes in heart rate and blood pressure were observed, in nine healthy subjects, during and after voluntary and electrically evoked isometric contractions of the triceps surae under conditions of local circulatory arrest. 2. The progressive increases in heart rate and blood pressure seen during 2 min voluntary and evoked contractions at 30% of maximal voluntary contraction were not significantly different in the two conditions. On cessation of contraction but with circulatory arrest maintained, heart rate fell to control levels while blood pressure fell to a similar though still significantly elevated level in both conditions. Elevated blood pressure was maintained for 2 min until the circulatory occlusion was removed; however it was maintained at a significantly higher level for the last 60‐90 s of occlusion following electrically evoked contractions compared to voluntary contraction. 3. Comparison of the responses to voluntary and involuntary electrically evoked contractions suggest that ‘central command’ is not necessary for the initial increases in heart rate and blood pressure to occur. In addition the removal of central command on cessation of contraction need not account for the return of heart rate to control levels or the drop in blood pressure at that time. Maintained blood pressure elevation during circulatory occlusion would seem to be due to the trapping of chemical substances within the muscle interstitium.
Ionic currents in single smooth muscle cells from the ureter of the guinea‐pig.
Authors: Imaizumi Y , Muraki K , Watanabe M
Published: December 2014

1. Ionic currents underlying the action potential were recorded from enzymatically isolated smooth muscle cells of guinea‐pig ureter. 2. The action potential recorded from a single cell was similar to that from a multicellular preparation. It showed repetitive spikes on a plateau potential which followed the first spike. Treatment with 10 mM‐tetraethylammonium (TEA) increased the amplitude and duration of the plateau phase and abolished the repetitive spikes. 3. Under voltage clamp mode, at least two (maybe three) kinds of outward currents were activated during depolarizing pulses. The main outward current was Ca2+‐dependent K+ current (IK(Ca], which was mostly blocked in Ca2+‐free solution, or by application of 1 mM‐cadmium (Cd2+) or 2 mM‐tetraethylammonium (TEA). IK(Ca) was greatly decreased by treatment with 5 mM‐caffeine or an addition of 10 mM‐EGTA in a pipette solution. 4. In the presence of 1 mM‐Cd2+ and 2 mM‐TEA, a small transient outward current remained. 4‐Aminopyridine (1 mM) suppressed the transient outward current by about 40%. Time‐ and voltage‐dependent delayed rectifier outward currents were small in ureter cells. An inwardly rectifying K+ current was not detected. 5. An application of 1 mM‐Cd2+, 5 mM‐cobalt (Co2+), 1 mM‐lanthanum (La3+) or 0.1 microM‐nifedipine completely blocked the action potential. Replacement of 80‐90% of extracellular Na+ with Li+ or Tris almost abolished the plateau potential and repetitive spikes but did not change significantly the first spike. 6. In the presence of 30 mM‐TEA, the inward current elicited by depolarization was monophasic and lasted for more than 1 s. Application of 1 mM‐Cd2+, 1 mM‐La3+, 0.1 microM‐nifedipine, or 5 mM‐Co2+ completely blocked inward current. The replacement (87%) of extracellular Na+ ions with Li+, Tris, sucrose or TEA speeded up the decay of inward current; the inward current decreased by 10‐60% at the end of a 500 ms pulse. 7. Even in low‐Na+ solution (120 mM‐TEA), the inactivation of ICa had a quite slow component (tau = 1 s), in addition to another faster component (tau = 100 ms) at 0 mV. When short depolarizing clamp pulses (50 ms) were repetitively applied at short intervals (50 ms) and with interpulse voltage of ‐10 or ‐20 mV to mimic the repetitive spikes on the plateau of the action potential, the decline of peak Ca2+ current during the train of pulses was smaller than the decay of Ca2+ current during a long pulse.(ABSTRACT TRUNCATED AT 400 WORDS)
Neurotensin facilitates release of substance P in the guinea‐pig inferior mesenteric ganglion.
Authors: Stapelfeldt W H , Szurszewski J H
Published: December 2014

1. Intracellular, electrophysiological techniques were combined with radio‐immunological, chromatographic and pharmacological techniques to determine if nerve terminals containing substance P mediated transient depolarizing responses of principal ganglion cells induced by neurotensin. Experiments were performed in vitro on guinea‐pig inferior mesenteric ganglia. 2. In 61% of principal ganglion cells tested in normal ganglia, neurotensin caused a transient membrane depolarization. In ganglia which were removed from animals which had been pre‐treated with capsaicin, transient responses to neurotensin were virtually abolished. 3. In normal ganglia, neurotensin increased the amplitude and duration of noncholinergic slow EPSPs evoked by electrical stimulation of the lumbar colonic nerve. Such increases were absent in ganglia obtained from animals pre‐treated with capsaicin. 4. In guinea‐pigs pre‐treated with capsaicin, the content of substance P‐like material was significantly reduced in inferior mesenteric and coeliac ganglia, dorsal root ganglia and lumbar spinal cord, compared to control animals. The content of substance P‐like material in segments of distal colon was slightly reduced. The content of vasoactive intestinal polypeptide‐, cholecystokinin‐ and bombesin‐like material in the same tissues from animals pre‐treated with capsaicin was not significantly different from control animals. 5. Chromatographic analysis using HPLC (high‐performance liquid chromatography) techniques revealed that the material depleted from inferior mesenteric and coeliac ganglia, dorsal root ganglia and lumbar spinal cord by capsaicin pre‐treatment co‐eluted with synthetic substance P. 6. Electrical stimulation of the lumbar colonic nerve released substance P‐like material from isolated inferior mesenteric ganglia as determined by radioimmunoassay of samples of superfusate. Exogenous administration of neurotensin caused a significant increase in the amount of substance P‐like material released during nerve stimulation. 7. Transient depolarizing responses evoked by neurotensin were markedly attenuated when ganglion cells were postsynaptically desensitized to exogenously administered substance P. 8. Taken together, these findings suggest that transient depolarizations mediated by an indirect action of neurotensin and facilitation of electrically evoked non‐cholinergic slow EPSPs by neurotensin involved presynaptic release of substance P from collateral nerve terminals of primary afferent nerve fibres in the inferior mesenteric ganglion. 9. It was suggested that under normal in vivo conditions, neurotensin or a C‐terminal‐related peptide contained in central preganglionic nerve endings might function as an excitatory neuromodulator to enhance the release of substance P from primary afferent nerve terminals thereby facilitating non‐cholinergic peripheral afferent synaptic input to prevertebral ganglion cells.
The ventilatory CO2 sensitivities from Read's rebreathing method and the steady‐state method are not equal in man.
Authors: Berkenbosch A , Bovill J G , Dahan A , DeGoede J , Olievier I C
Published: December 2014

1. The ventilatory response to changes in end‐tidal carbon dioxide tension during hyperoxia, obtained with Read's rebreathing method and a steady‐state technique, were compared. 2. In ten young male subjects, forty successful rebreathing and thirteen steady‐state experiments were performed on thirteen different morning sessions. 3. In all subjects the ventilatory CO2 sensitivities obtained with the rebreathing method (Sr) were appreciably larger than the steady‐state CO2 sensitivities (Ss). The ratio Sr/Ss ranged from 1.40 to 2.59 with a mean value of 1.85. 4. We argue that these results can be explained by considering the effect of changes in cerebral blood flow upon increasing the arterial CO2 tension during rebreathing and the steady state. 5. We conclude that in general the CO2 sensitivity obtained with Read's rebreathing method does not represent the steady‐state CO2 sensitivity.
Effect of nocodazole on the water permeability response to vasopressin in rabbit collecting tubules perfused in vitro.
Authors: Phillips M E , Taylor A
Published: December 2014

1. The effect of the microtubule‐disruptive agent, nocodazole (methyl [5‐(2‐thienylcarbonyl)‐1H‐benzimidazol‐2‐yl] carbamate), on the water permeability response to vasopressin or the synthetic cyclic AMP analogue, 8‐parachlorophenylthio‐cyclic AMP (8‐CPT‐cAMP), has been investigated in isolated cortical collecting tubules from rabbit kidneys, perfused in vitro. 2. Pre‐treatment with nocodazole, 1‐4 micrograms ml‐1, had no significant effect on basal water permeability, but inhibited the increase in hydraulic conductivity elicited by vasopressin, 50 microU ml‐1, in a dose‐dependent manner. Inhibition of the response to the hormone averaged 65 +/‐ 6% (n = 8, P less than 0.001) at a nocodazole concentration of 4 micrograms ml‐1. 3. Nocodazole, 1‐4 micrograms ml‐1, had no effect on the increase in lumen‐negative potential difference (PD) induced by the hormone. 4. Pre‐treatment with nocodazole, 4 micrograms ml‐1, inhibited the development of the water permeability response to 8‐CPT‐cAMP, 1.8 x 10(‐5) M, by 45 +/‐ 7% (n = 7, P less than 0.001). 5. When collecting tubules were exposed to nocodazole, 4 micrograms ml‐1, after the hydrosmotic response to vasopressin had been fully established, the drug had no inhibitory effect on the maintenance of a high water permeability. 6. The results are consistent with the view that cytoplasmic microtubules play a role in the initiation of the water permeability response to vasopressin in the mammalian cortical collecting tubule at a cellular site beyond the generation of cyclic AMP.
Factors affecting the accuracy of position matching at the proximal interphalangeal joint in human subjects.
Authors: Ferrell W R , Milne S E
Published: December 2014

1. The ability of normal subjects to match finger position at the proximal interphalangeal (PIP) joint was tested under a number of different conditions. One finger (target finger) was passively displaced in a pseudorandom manner whilst the other (matching) finger was actively positioned by the subject. 2. Digital nerve block of the target finger resulted in the matching finger only being displaced through a small range ('range compression') whilst anaesthesia of the matching finger produced the opposite effect ('range expansion'). 3. When the finger is unanaesthetized, the velocity of displacement of the target finger from one position to the next does not affect the accuracy of position matching. However, during digital nerve block of the target finger, matching errors increase with decreasing velocity. 4. The impairment of matching performance during digital nerve block is due specifically to loss of input from receptors in and around the PIP joint, as anaesthesia of the tip of the finger to produce any significant decrement in matching accuracy. 5. The results show that muscle receptors contribute to position sense at this joint but are not the exclusive source of proprioceptive sensations.
Dihydropyridine‐sensitive low‐threshold calcium channels in isolated rat hypothalamic neurones.
Authors: Akaike N , Kostyuk P G , Osipchuk Y V
Published: December 2014

1. Low‐voltage‐activated Ca2+ channels which produce a transient inward current were studied in neurones freshly isolated from the ventromedial hypothalamic region of the rat. Membrane currents were recorded using a suction‐pipette technique which allows for internal perfusion under a single‐electrode voltage clamp. A concentration‐jump technique was also used for rapid drug application. 2. In most cells superfused with 10 mM‐Ca2+, a transient inward Ca2+ current was evoked by a step depolarization to potentials more positive than ‐65 mV from a holding potential of ‐100 mV. Such a low‐threshold Ca2+ current could easily be separated from a high‐threshold, steady type of Ca2+ current by selecting the holding and test potential levels, as well as by resistance to the wash‐out during cell dialysis. 3. Activation and inactivation processes of the low‐threshold Ca2+ current were highly potential dependent at 20‐22 degrees C. For a test potential change from ‐60 to +20 mV, the time to peak of the current decreased from 45 to 9 ms, and the time constant of the current decay decreased from 90 to 40 ms. The steady‐state inactivation occurred at very negative potentials, reaching a 50% level at ‐93 mV. Recovery from inactivation showed a time constant between 2.63 and 0.94 s for a potential change from ‐80 to ‐120 mV. 4. The amplitude of the low‐threshold Ca2+ current depended on the external Ca2+ concentration [( Ca2+]o), approaching saturation at 100 mM [Ca2+]o. Ba2+ substituted for Ca2+ reduced the current amplitude by 30‐50% while Sr2+ produced no definite changes in the current amplitude. 5. The low‐threshold Ca2+ current was blocked by various di‐ or trivalent cations in the sequence of La3+ greater than Zn2+ greater than Cd2+ greater than Ni2+ greater than Co2+. The corresponding apparent dissociation constants (KD) were 7 x 10(‐7), 1 x 10(‐4), 3 x 10(‐4), 6 x 10(‐4) and 3 x 10(‐3) M. 6. Various organic Ca2+ antagonists were effective in blocking the low‐threshold Ca2+ current in the following sequence: flunarizine greater than nicardipine greater than nifedipine greater than nimodipine greater than D600 (methoxyverapamil) greater than diltiazem. The corresponding KDs were 7 x 10(‐7), 3.5 x 10(‐6), 5 x 10(‐6), 7 x 10(‐6), 5 x 10(‐5) and 7 x 10(‐5) M. These Ca2+ antagonists induced a use‐dependent decrease in the current amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of catecholamines on deformability of red cells from trout: relative roles of cyclic AMP and cell volume.
Authors: Chiocchia G , Motais R
Published: December 2014

1. In the presence of catecholamine the nucleated red blood cells of trout show a large increase in cell volume as a result of an accumulation of sodium and chloride due to activation of an amiloride‐sensitive, cyclic AMP‐dependent Na+‐H+ exchanger allowing Na+ to enter in exchange for internal H+. 2. The activation of this cyclic AMP‐dependent Na+‐H+ exchange is considered to be involved in an adaptive response to hypoxia by increasing the oxygen‐carrying capacity of erythrocytes. But cell swelling could increase resistance to blood flow and thus impair the expected physiological advantages for oxygen transport. The effect of catecholamine on the deformability properties of the red blood cells has been studied by measuring the rate at which blood flows through a Nucleopore filter (5 microM). 3. The results show that stimulation by catecholamine in fact increases the erythrocyte deformability, a response which must favour the supply of oxygen at the tissue level. 4. Hormonal stimulation increases the cellular cyclic AMP content (and cyclic AMP‐dependent phosphorylation of cytoskeleton proteins could influence cell deformability) and the cell volume. It has been shown that when cellular cyclic AMP content is increased under conditions where the cell cannot swell, the erythrocyte becomes more rigid and not more deformable. Conversely the results show a systematic coincidence between cell swelling and deformability increase. The precise way in which volume change and deformability are interrelated needs more study.
Two types of calcium currents in single smooth muscle cells from rat portal vein.
Authors: Loirand G , Mironneau C , Mironneau J , Pacaud P
Published: December 2014

1. Using the whole‐cell recording mode of the patch‐clamp technique, we investigated the calcium currents in isolated cells from rat portal vein in short‐term primary culture. 2. From a holding potential of ‐70 mV the cells presented two types of calcium currents with 5 mM‐extracellular calcium: one type was activated by small depolarizations and inactivated quickly (fast calcium current), whereas the other required stronger depolarizations for activation and inactivated more slowly (slow calcium current). 3. Isradipine (PN 200‐110) blocked the slow calcium current at concentrations 300 times lower than those used to block the fast inward current. The isradipine‐induced inhibition was voltage‐dependent for the slow calcium current and voltage‐independent for the fast calcium current. 4. The slow calcium current was lost during internal perfusion with a 0.5 microM‐Ca2+ containing solution, and during stimulation of the cell at high frequencies (0.1‐0.2 Hz) within 5‐10 min. The fast calcium current was unchanged under these experimental conditions. 5. Steady‐state inactivation curves for both fast and slow calcium currents showed differences in their voltage dependence. Half‐maximal and complete inactivations of the fast calcium current were obtained at ‐50 and ‐30 mV while those of the slow calcium current were obtained at ‐20 and +10 mV. 6. Studied with the two‐pulse protocol, inactivation of the slow calcium current was dependent on both membrane potential and calcium influx while that of the fast calcium current appeared only dependent on membrane potential. 7. Two types of calcium currents, differing in potential dependence of inactivation, and in sensitivities to dihydropyridines, stimulation frequency and intracellular calcium concentration were identified in cultured smooth muscle cells isolated from portal vein.
Calcium currents in the normal adult rat sympathetic neurone.
Authors: Belluzzi O , Sacchi O
Published: December 2014

1. The calcium currents evoked by membrane depolarization in the mature and intact rat sympathetic neurone have been studied at 37 degrees C using two‐electrode voltage‐clamp analysis. 2. Under conditions that eliminate Na+ and K+ currents and 5 mM‐external Ca2+, inward currents were observed that activated at about ‐30 mV and reached maximum amplitude between 0 and +10 mV with time‐to‐peak values (2.7‐1.9 ms) decreasing with increasing membrane depolarization. Thereafter, calcium current (ICa) decayed to a virtually zero level with maintained depolarization. Two exponentials were required to describe the total inactivation process. The faster rate (tau = 29.3‐17.6 ms) is ten times the slower rate and proved to be only slightly voltage‐dependent. Double‐pulse experiments gave a similar time course of turn‐off. 3. No steady‐state inactivation was removed at holding potentials between ‐40 and ‐70 mV and indirect data suggest that all the ICa was available at ‐50 mV. Within the ‐30 to ‐50 mV holding potential range no significant modifications either in the final amount of ICa inactivation or in the inactivation time constant values were detected. 4. After an initial 100 ms, recovery from inactivation followed a single‐exponential process with a mean time constant value of 1.54 s at ‐50 mV. 5. The kinetics of ICa observed in this neurone were consistent with the existence of a single class of Ca2+ channels. For times up to 20 ms, ICa is described reasonably well by a Hodgkin‐Huxley c2hc scheme. The activation time constant was 0.57 ms close to threshold and 0.29 ms at +30 mV. Deactivation occurred with a similar fast time course. The steady‐state value of the variable c was evaluated in the ‐40 to +20 mV voltage range: 9.9 mV are required to change c infinity e‐fold. 6. Following previous analyses, we have formulated a mathematical model which incorporates the present ICa kinetic equations with Hodgkin‐Huxley‐type gating mechanisms for INa, IA and IK(V) conductances. The Ca2+ load of the neurone proved to be basically an ‘off’ effect and to be governed by the duration of the action potential falling phase. The model is consistent with the experimental observations indicating that Ca2+ channels probably do not have an important direct electrical function in the sympathetic neurone spike at normal membrane potential levels.(ABSTRACT TRUNCATED AT 400 WORDS)
Augmentation of secretagogue‐induced amylase secretion in pancreatic acini of heat‐exposed rats.
Authors: Habara Y
Published: December 2014

1. The effects of prolonged heat exposure on pancreatic exocrine secretion were investigated to evaluate the involvement of the insulin‐pancreatic acinar axis. Rats were kept at 34 degrees C and a relative humidity of 40% for 2 weeks with or without insulin administration. Control rats were housed at the thermoneutral temperature of 25 degrees C. By using isolated acini, secretory function was examined at the cellular level. 2. Without insulin treatment, acinar amylase concentration, expressed per microgram of cellular protein, was increased by heat exposure, while trypsinogen concentration, expressed per microgram of acinar DNA, decreased. The ratio of acinar amylase to trypsinogen increased significantly from 2.82 to 5.69 by prolonged heat exposure. With insulin treatment, the heat‐induced increase in amylase activity was lessened but the decrease in trypsinogen remained unchanged. The ratio was somewhat lessened to 4.66. 3. In acini from saline‐treated rats, amylase release in response to varying concentrations of cholecystokinin octapeptide or carbamylcholine was significantly augmented by prolonged heat exposure. As a result, the dose‐response curve shifted upwards. However, in acini from insulin‐treated rats, the increase in secretory response was lessened, similar to the effect on acinar content. On the other hand, changes in trypsinogen release were not as notable as those in amylase release. The ratio of amylase to trypsinogen in pancreatic juice released by 100 pM‐cholecystokinin octapeptide increased from 1.56 to 3.04 in saline‐treated rats and from 1.60 to 2.34 in insulin‐treated rats. 4. In heat‐exposed, saline‐treated rats the plasma concentrations of glucose and insulin were significantly elevated, while in insulin‐treated rats these increases were lessened and the elevation of plasma insulin concentration was no longer significant. 5. It is suggested that heat exposure elevates resting plasma glucose concentration, probably because of decreased metabolic activity, which results in a concomitant rise in plasma insulin concentration. This hormonal change most likely is a major cause of augmentation of acinar amylase synthesis and of the resultant potentiation of stimulus‐secretion coupling via an insulin‐pancreatic acinar axis. Heat exposure modified pancreatic exocrine function in the opposite direction to what occurred in cold‐exposed animals. It was confirmed that changes in pancreatic exocrine function via a modification of the insulin‐pancreatic acinar axis can actually occur under normal physiological circumstances. From the nutritional point of view, this modification by ambient temperature should be taken into consideration.
Spatial spread of in‐field afferent inhibition in the cat's spinocervical tract.
Authors: Noble R , Short A D
Published: December 2014

1. Extracellular microelectrode recordings were made from twenty‐three spinocervical tract (SCT) cells in the lumbar spinal cord of cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Excitation and inhibition of the cells were elicited by applying small brief (4 mN, 60 ms) localized jets of air to the clipped hair in and around the receptive fields. 2. Receptive field extents ranged from 40 to 180 mm. Excitation occurred in the period 30‐130 ms after the start of the stimulus, and in‐field afferent inhibition from 130 ms up to 700 ms or more. The inhibition was manifest as a reduction in background discharge and as a reduction in responsiveness to a test stimulus which followed a conditioning stimulus. 3. When the conditioning stimulus was spatially separated from the test stimulus, the degrees of in‐field afferent inhibition depended on the spatial separation, even when both were within the excitatory receptive field. The spatial spread of in‐field afferent inhibition was limited to 100 mm or less. 4. In two units only, afferent inhibition was produced from a narrow strip just outside the excitatory receptive field. In the other units, it could only be produced from within the excitatory receptive field. 5. The results suggest that the inhibitory input to SCT cells is organized in subdomains no more than 100 mm across, which may correspond to the receptive fields of interneurones between the primary afferent fibres and the SCT cells.
Synchronization of motor unit firing during different respiratory and postural tasks in human sternocleidomastoid muscle.
Authors: Adams L , Datta A K , Guz A
Published: December 2014

1. Motor unit firing has been studied in human sternocleidomastoid muscle. 2. Two needle electrodes were inserted into the muscle and the activity of pairs of motor units recorded during (a) reflex hypercapnic obstructed breathing, (b) eucapnic voluntary copying of (a) against the same inspiratory resistance and (c) voluntary copying of (a) without any resistance, accompanied by isometric neck rotation. 3. Cross‐correlation histograms of the firing of unit pairs showed a clear central peak, indicative of synchronization. The mean duration of the peak during voluntary breathing was 25 ms (range 9‐40 ms). There was no difference in duration of synchronization during the different tasks. 4. For the duration of the synchronization peak, the mean strength of synchronization expressed as the number of concomitant discharges of the two units as a proportion of the total number of discharges was 0.026 (range 0.011‐0.058) for reflex hypercapnic obstructed breathing. For the same unit pairs the strength of synchronization for isometric neck rotation was the same as that during reflex hypercapnic breathing but for voluntary obstructed breathing it was, on average, threefold greater. 5. In three out of twenty‐two motor units studied, ‘discharge’ occurred with an interval of less than 10 ms (‘doublet’ firing) at the onset of each inspiration during both types of obstructed breathing; this was rarely observed during neck rotation. 6. The results are interpreted in terms of different synaptic drives to the motor units during the three different tasks.