bluuebunny/crossref_metadata_2025 huggingface dataset:
Vasoactive intestinal polypeptide modulation of nicotinic ACh receptor channels in rat intracardiac neurones.
Authors: Cuevas J , Adams D J
Published: December 2014

1. The effects of vasoactive intestinal polypeptide (VIP) on isolated parasympathetic neurones of rat intracardiac ganglia were examined under voltage clamp using dialysed and perforated patch whole‐cell and excised outside‐out membrane patch recording configurations. 2. VIP reversibly potentiated nicotinic ACh‐evoked whole‐cell currents, with half‐maximal potentiation (EC50) obtained with 260 pM VIP. However, VIP had no effect on muscarinic ACh‐evoked currents, ATP‐evoked currents, or depolarization‐activated ionic currents in these neurones. 3. VIP‐induced potentiation of nicotinic ACh‐evoked whole‐cell currents was observed following cell dialysis, and was inhibited reversibly by bath application of the VIP receptor‐binding inhibitor L‐8‐K (5 microM) or the neuronal nicotinic receptor antagonist mecamylamine (3 microM). 4. The signal transduction pathway mediating VIP‐induced potentiation of nicotinic ACh‐evoked currents involves a guanine nucleotide‐binding protein (G‐protein) but not cyclic AMP. Intracellular application of 100 microM GDP‐beta‐S, or pre‐incubation of neurones with pertussis toxin, inhibited VIP‐induced potentiation of ACh‐evoked whole‐cell currents. 5. In outside‐out membrane patches, co‐application of ACh (4 microM) and VIP (4 nM) decreased the duration of closings between bursts and clusters of bursts of ACh single‐channel activity relative to control (4 microM, ACh alone). VIP, however, did not alter single ACh receptor channel current amplitude, duration of closings and openings within a burst, or mean burst duration. 6. VIP‐induced modification of nicotinic ACh receptor channel kinetics results in an increase in the open‐channel probability which is sufficient to account for the VIP‐mediated potentiation of nicotinic ACh‐evoked whole‐cell currents. 7. The potentiation of nicotinic ACh‐evoked currents by VIP is likely to account for the altered neuronal activity observed in the mammalian intracardiac ganglia in vivo and consequent changes in heart rate and cardiac contractility.
Effects of GABA agonists and antagonists on temperature‐sensitive neurones in the rat hypothalamus.
Authors: Yakimova K , Sann H , Schmid H A , Pierau F K
Published: December 2014

1. Extracellular recordings were obtained from 94 warm‐sensitive, 6 cold‐sensitive and 117 temperature‐insensitive neurones in slices of the hypothalamic medial preoptic area of rats, to determine the effect of the GABAA agonist muscimol, the GABAA antagonist bicuculline, the GABAB agonist baclofen and the GABAB antagonist phaclofen on tonic activity and temperature sensitivity. 2. Muscimol and baclofen dose‐dependently inhibited the tonic activity of 69% (36/52) and 97% (36/37) of the hypothalamic neurones, respectively, regardless of their type of thermosensitivity. In contrast, the GABAA antagonist bicuculline increased the tonic activity of the majority of neurones (58/83), while the GABAB antagonist phaclofen increased neuronal activity only in the high dose of 100 microM. 3. The temperature sensitivity of hypothalamic neurones was only changed by ligands of GABAB receptors, and this effect was restricted to warm‐sensitive neurones. The temperature coefficient (TC) was significantly increased by the GABAB agonist baclofen (delta TC = 0.69 +/‐ 0.11 imp s‐1 degree C‐1, P < 0.01, n = 18). In contrast, the GABAB antagonist phaclofen (10 microM) decreased the temperature sensitivity (delta TC = ‐0.67 +/‐ 0.09 imp s‐1 degree C‐1, P < 0.01, n = 10) in doses which did not affect tonic activity. 4. The increase in temperature sensitivity due to the GABAB agonist baclofen was significantly enhanced by co‐perfusion of the GABAA antagonist bicuculline, indicating an interaction of GABAA and GABAB receptor‐mediated mechanisms with regard to neuronal thermosensitivity. 5. The results suggest that neurones in the medical preoptic area are subject to GABA‐mediated tonic inhibition resulting in modulation of tonic activity and temperature sensitivity of warm‐sensitive neurones possibly involved in the control of body temperature. The data support the hypothesis that the hypo‐ or hyperthermic action of an endogenous substance is related to its effect on the thermosensitivity rather than on tonic activity of hypothalamic neurones.
Calorigenic effect of diiodothyronines in the rat.
Authors: Lanni A , Moreno M , Lombardi A , Goglia F
Published: December 2014

1. In hypothyroid rats, we determined the effects of administration of different doses of 3,3',5‐triiodo‐L‐thyronine (T3), 3,3'‐diiodo‐L‐thyronine (3,3'‐T2) and 3,5‐diiodo‐L‐thyronine (3,5‐T2) (‘T2 isomers’ refers specifically to these latter two isomers throughout this paper) on resting metabolism (RM) and on the oxidative capacity (measured as cytochrome oxidase activity) of tissues that are metabolically very active. 2. The T2 isomers induced a dose‐dependent calorigenic effect when injected I.P. into hypothyroid rats. The increase in RM was already evident at a dose of 2.5 micrograms (100 g body wt)(‐1), and the greatest effect was observed at the highest dose, 10 micrograms (100 g body wt)(‐1), when RM reached a value not significantly different from that of the euthyroid controls (1.92 +/‐ 0.08 and 1.93 +/‐ 0.13 (1 O2) kg(‐1) h(‐1) for 3,5'‐T2, respectively, vs. 2.1 +/‐ 0.12 (1 O2) kg(‐1) h(‐1) for euthyroid controls). T3 administration restored RM to normal euthyroid values, even at a dose of 2.5 micrograms (100 g body wt)(‐1). 3. The effect of T2 isomers on RM was paralleled by an increase in the oxidative capacity of tissues that are metabolically very active (liver, skeletal muscle, brown adipose tissue (BAT) and heart). The increases were between 33% (liver + 3,3'‐T2) and 63% (muscle + 3,3'‐T2). By contrast, T3 induced its greatest effect on the liver, with a smaller effect on skeletal muscle, but no significant stimulation in heart and BAT, whatever the dose. 4. These results suggest that T8 isomers might be mediators of the direct thyroid hormone regulation of energy metabolism.
The effect of low‐dose acetazolamide on the ventilatory CO2 response curve in the anaesthetized cat.
Authors: Wagenaar M , Teppema L , Berkenbosch A , Olievier C , Folgering H
Published: December 2014

1. The effect of 4 mg kg‐1 acetazolamide (I.V.) on the slope (S) and intercept on the Pa,CO2 axis (B) of the ventilatory CO2 response curve of anaesthetized cats with intact or denervated carotid bodies was studied using the technique of dynamic end‐tidal forcing. 2. This dose did not induce an arterial‐to‐end‐tidal PCO2 (P(a‐ET),CO2) gradient, indicating that erythrocytic carbonic anhydrase was not completely inhibited. Within the first 2 h after administration, this small dose caused only a slight decrease in mean standard bicarbonate of 1.8 and 1.7 mmol l‐1 in intact (n = 7) and denervated animals (n = 7), respectively. Doses of acetazolamide larger than 4 mg kg‐1 (up to 32 mg kg‐1) caused a significant increase in the P(a‐ET),CO2 gradient. 3. In carotid body‐denervated cats, 4 mg kg‐1 acetazolamide caused a decrease in the CO2 sensitivity of the central chemoreflex loop (Sc) from 1.52 +/‐ 0.42 to 0.96 +/‐ 0.32 l min‐1 kPa‐1 (mean +/‐ S.D.) while the intercept on the Pa,CO2 axis (B) decreased from 4.5 +/‐ 0.5 to 4.2 +/‐ 0.7 kPa. 4. In carotid body‐intact animals, 4 mg kg‐1 acetazolamide caused a decrease in the CO2 sensitivity of the peripheral chemoreflex loop (Sp) from 0.28 +/‐ 0.18 to 0.19 +/‐ 0.12 l min‐1 kPa‐1. Se and B decreased from 1.52 +/‐ 0.55 to 0.84 +/‐ 0.21 l min‐1 kPa‐1, and from 4.0 +/‐ 0.5 to 3.0 +/‐ 0.6 kPa, respectively, not significantly different from the changes encountered in the denervated animals. 5. It is argued that the effect of acetazolamide on the CO2 sensitivity of the peripheral chemoreflex loop in intact cats may be caused by a direct effect on the carotid bodies. Both in intact and in denervated animals the effects of the drug on Sc and B may not be due to a direct action on the central nervous system, but rather to an effect on cerebral vessels resulting in an altered relationship between brain blood flow and brain tissue PCO2.
Rostrocaudal gradient of electrical activation in the parasternal intercostal muscles of the dog.
Authors: Legrand A , Brancatisano A , Decramer M , De Troyer A
Published: December 2014

1. Because the inspiratory mechanical advantage of the canine parasternal intercostal muscles is greatest in the third interspace and decreases gradually in the caudal direction, the electromyograms of these muscles in interspaces 3, 5 and 7 have been recorded in anaesthetized, spontaneously breathing dogs. Each activity was expressed as a percentage of the activity measured during tetanic, supramaximal stimulation of the internal intercostal nerve (maximal activity). 2. Parasternal inspiratory activity during resting, room air breathing was invariably greater in the third than in the fifth interspace (62.0 +/‐ 6.0 vs. 41.3 +/‐ 4.6% of maximal activity; P < 0.001) and smallest in the seventh interspace (22.8 +/‐ 2.7% of maximal activity; P < 0.001). This distribution of activity persisted during hyperoxic hypercapnia and during breathing against increased inspiratory airflow resistance. 3. This rostrocaudal distribution of activity also persisted after complete paralysis of the diaphragm as well as after deafferentation of the ribcage. 4. Studies of the distribution of the muscle fibre types indicated that the parasternal intercostals in all interspaces had a higher proportion of slow‐twitch oxidative (SO; type I) fibres than fast‐twitch oxidative‐glycolytic (FOG; type II a) fibres. 5. Thus the topographic distribution of parasternal inspiratory activity along the rostrocaudal axis of the ribcage is precisely matched with the topographic distribution of mechanical advantage. This extraordinarily effective pattern of activation probably results from the unequal distribution of central inputs throughout the parasternal motoneurone pool.
Increase in ATP consumption during shortening in skinned fibres from rabbit psoas muscle: effects of inorganic phosphate.
Authors: Potma E J , Stienen G J
Published: December 2014

1. The influence of inorganic phosphate (P(i)) on the relationship between ATP consumption and mechanical performance under isometric and dynamic conditions was investigated in chemically skinned single fibres or thin bundles from rabbit psoas muscle. Myofibrillar ATPase activity was measured photometrically by enzymatic coupling of the regeneration of ATP to the oxidation of NADH. NADH absorbance at 340 nm was determined inside a miniature (4 microliters) measuring chamber. 2. ATP consumption due to isovelocity shortenings was measured in the range between 0.0625 and 1 L0 s‐1(L0: fibre length previous to shortening, corresponding to a sarcomere length of 2.64 microns), in solutions without added P(i) and with 30 mM P(i). To get an estimate of the amount of ATP utilized during the shortening phase, quick releases of various amplitudes were also performed. 3. After quick releases, sufficiently large that force dropped to zero, extra ATP was hydrolysed which was largely independent of the amplitude of the release and of the period of unloaded shortening. This extra amount, above the isometric ATP turnover, corresponded to about 0.7 and 0.5 ATP molecules per myosin head at 0 and 30 mM P(i), respectively. 4. ATP turnover during the isovelocity shortenings was higher than isometric turnover and increased with increasing shortening velocity up to about 2.7 times the isometric value. At low and moderate velocities of shortening (< 0.5 L0 s‐1), P(i) reduced ATP turnover during isovelocity shortening and isometric ATP turnover to a similar extent, i.e. a decrease to about 77% between 0 and 30 mM added P(i). 5. The extra ATP turnover above the isometric value, resulting from isovelocity shortenings studied at different speeds, was proportional to the power output of the preparation, both in the absence and presence of added [P(i)]. 6. The effect of shortening velocity and [P(i)] on energy turnover can be understood in a cross‐bridge model that consists of a detached, a non‐ or low‐force‐producing, and a force‐producing state. In this model, mass action of P(i) influences the equilibrium between the force‐producing and the non‐or‐low‐force‐producing cross‐bridges, and shortening enhances cross‐bridge detachment from both attached states.
Effect of metabolic inhibition on K+ channels in pyramidal cells of the hippocampal CA1 region in rat brain slices.
Authors: Hyllienmark L , Brismar T
Published: December 2014

1. The effect of metabolic inhibition on membrane potential and ionic conductances of K+ channels was studied with the patch‐clamp technique in pyramidal cells in the CA1 region of the hippocampus. Individual cells were visualized in brain slices from rats aged between 9 and 19 days using infrared video microscopy. Excitability was inhibited by tetrodotoxin. 2. Dinitrophenol (DNP), carbonyl cyanide p‐trifluoromethoxyphenylhydrazone (FCCP) and cyanide hyperpolarized the majority of the cells. The resting potential (V) was ‐55.3 +/‐ 0.23 mV (n = 147). In response to DNP the change in V was ‐3.9 +/‐ 0.76 mV (n = 59), with a normal distribution ranging between +9.0 and ‐16 mV. 3. Metabolic inhibition increased the resting conductance (grest) and the conductance related to the delayed outward current measured at V = ‐20 mV (g‐20), and decreased the conductance of the early outward A‐current (gA). The changes in grest and g‐20 were transient and differed from the time‐dependent changes seen in control cells. 4. Tolbutamide reversed the hyperpolarization and the increase in grest. Glibenclamide, apamin and charybdotoxin were ineffective. 5. The presence of ATP (2 mM) in the pipette solution did not influence the change in grest. ATP did, however, affect the time‐dependent decline in gA and g‐20, which demonstrated that cells had been perfused. 6. Cadmium (0.5 mM) reduced the increase in g‐20 and grest obtained with DNP, although it did not prevent the effect of DNP on grest. This indicates that the action of DNP involves an elevation of intracellular [Ca2+]. 7. It is concluded that metabolic inhibition causes changes in the function of several types of K+ channels in CA1 cells. A transient opening of a tolbutamide‐sensitive K+ channel could explain the increase in grest and the hyperpolarization observed in most cells.
Voltage‐dependent blockage of Ca(2+)‐permeable AMPA receptors by joro spider toxin in cultured rat hippocampal neurones.
Authors: Iino M , Koike M , Isa T , Ozawa S
Published: December 2014

1. The effect of synthetic joro spider toxin (JSTX‐3) on alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor channels in cultured rat hippocampal neurones was investigated using the whole‐cell patch‐clamp technique. 2. A population of cultured neurones had AMPA receptors with strong inward rectification and substantial Ca2+ permeability (type II neurones), whereas most neurones (type I neurones) had slight outward rectification and little Ca2+ permeability. JSTX‐3 selectively suppressed the inwardly rectifying and Ca(2+)‐permeable AMPA receptors expressed in type II neurones without affecting AMPA receptors in type I neurones. 3. The effect of JSTX‐3 on the Ca(2+)‐permeable AMPA receptors was use and voltage dependent. In the steady state, current responses induced by ionophoretic applications of kainate (a non‐desensitizing agonist of AMPA receptors) were suppressed by the toxin in a dose‐dependent manner at negative potentials (IC50 = 56 nM at ‐60 mV). 4. At the standard membrane potential (‐60 mV), recovery from the blockage by JSTX‐3 was very slow. Even after washout for more than 7 min, the recovery was only partial. However, the blockage was completely removed immediately after application of a +60 mV voltage pulse for 5 s in conjunction with a single ionophoretic application of kainate.
Characterization of an ultrarapid delayed rectifier potassium channel involved in canine atrial repolarization.
Authors: Yue L , Feng J , Li G R , Nattel S
Published: December 2014

1. Depolarizing pulses positive to 0 mV elicit a transient outward current (Ito) and a sustained ‘pedestal’ current in canine atrial myocytes. The pedestal current was highly sensitive to 4‐aminopyridine (4‐AP) and TEA, with 50% inhibitory concentrations (EC50) of 5.3 +/‐ 0.7 and 307 +/‐ 25 microM, respectively. When the pedestal current was separated from Ito with prepulses or by studying current sensitive to 10 mM TEA, it showed very rapid activation and deactivation. We therefore designated the current IKur,d, for ‘ultrarapid delayed rectifier, dog’. IKur,d inactivation was bi‐exponential, with mean time constants of 609 +/‐ 91 and 5563 +/‐ 676 ms during a 20 s pulse to +40 mV. 2. The reversal potential of IKur,d tail currents are dependent on extracellular potassium concentration ([K+]o; slope, 54.7 mV decade‐1). The envelope of tails test was satisfied and the current inwardly rectified at > or = +40 mV. The current was insensitive to E‐4031, dendrotoxin and chloride substitution, but was inhibited by barium, with an EC50 of 1.65 mM. Lanthanum ions caused a positive shift in voltage dependence without producing direct inhibition. 3. Single‐channel activity was observed in cell‐attached, inside‐out and outside‐out patches. Upon depolarization from ‐50 to +30 mV, single channels had similar time constants and [K+]o dependence to whole‐cell current. Channel open probability (Po) increased with depolarization in a saturable fashion and the Po‐voltage relation had a half‐activation voltage and slope factor similar to whole‐cell IKur,d. 4. Unitary channel current was linearly related to depolarization potential to +40 mV; at more positive potentials, inward rectification occurred. The unitary conductance was 20.3 and 35.5 pS for an [K+]o of 5.4 and 130 mM, respectively. Single‐channel activity was strongly inhibited by 50 microM 4‐AP or 10 mM TEA. Both 4‐AP and TEA decreased open time, suggesting open‐channel block. 5. Selective inhibition of IKur,d with 50 microM 4‐AP or 0.3‐5 mM TEA prolonged canine atrial action potentials, indicating that IKur,d contributes to canine atrial repolarization. The single‐channel and macroscopic properties of IKur,d have many similarities to those of currents carried by Kv3.1 cloned channels and our findings thus suggest a possible role for Kv3.1 channels in cardiac repolarization.
Cotransport of H+, lactate and H2O by membrane proteins in retinal pigment epithelium of bullfrog.
Authors: Zeuthen T , Hamann S , la Cour M
Published: December 2014

1. The interaction between H+, lactate and H2O fluxes in the retinal membrane of the pigment epithelium from bullfrog Rana catesbiana was studied by means of ion‐selective micro‐electrodes. 2. Changes in intracellular pH and cell volume were recorded in response to abrupt changes in retinal solution concentration and/or osmolarity. 3. Two parallel pathways for water transport were identified across the retinal membrane, an osmotic one with a hydraulic water permeability of 3.2 x 10(‐4) cm s‐1 (osmol l‐1)‐1 and one which depended on the presence of lactate. 4. Addition of sodium lactate to the retinal solution caused cell shrinkages that were small compared with those produced by mannitol. The reflection coefficient for sodium lactate was 0.25. 5. Isosmotic replacement of Cl‐ with lactate caused an influx of water. Simultaneous acidification of the retinal solution from pH 7.4 to 6.4 enhanced the effect. The influx of water could proceed against osmotic gradients elicited by mannitol. 6. The interdependence of the fluxes of H+, lactate and H2O can be described as cotransport: the fluxes had a fixed ratio of about 109 mmol of lactic acid per litre of water, the flux of one species was able to energize the flux of the other two, and the fluxes exhibited saturation for increasing driving forces. 7. The Gibbs equation gives an accurate quantitative description of these coupled fluxes.
The influence of muscle spindle discharge on the human H reflex and the monosynaptic reflex in the cat.
Authors: Wood S A , Gregory J E , Proske U
Published: December 2014

1. Experiments were carried out to test the effect of changes in spindle resting discharge on the size of monosynaptic reflexes in the cat and on the H reflex in humans. Resting discharge was altered by contracting the triceps surae muscle at longer (hold‐long) or shorter (hold‐short) lengths than that at which the reflex was tested. 2. The reflex in the cat was larger after hold‐long than after hold‐short conditioning, and the difference, after an initial decline, was well maintained. For the human H reflex a similar pattern was observed except that 15 s after muscle conditioning the difference in reflex size had disappeared. 3. Monosynaptic reflex depression immediately after hold‐long conditioning, when most of the muscle spindles are silent, was attributed to the high level of spindle discharge during the immediately preceding hold‐long period. The time course of this inhibition was too long to be accounted for by presynaptic inhibition. 4. In the cat heteronymous muscle conditioning was used to test whether presynaptic inhibition could be responsible for reflex depression using the synergist muscle pair lateral gastrocnemius‐soleus and medial gastrocnemius. Conditioning one of the pair did not affect the reflex in the other, the opposite result to that expected with presynaptic inhibition. A similar experiment in which the triceps H reflex in human subjects was facilitated by a quadriceps volley gave the same result. 5. Thus this study presents evidence that monosynaptic reflexes are depressed by the on‐going discharge of muscle spindles in the homonymous muscle, but that this depression does not appear to involve "classical' presynaptic inhibition.
Heat‐evoked vasodilatation in human hairy skin: axon reflexes due to low‐level activity of nociceptive afferents.
Authors: Magerl W , Treede R D
Published: December 2014

1. Spreading vasodilatation of the axon reflex type was evoked by contact heat stimulation of the hairy skin in the human forearm (13.3 cm2 stimulus area) and was detected by laser Doppler flowmetry at 8, 19 and 30 mm distance. 2. From a base temperature of 35 degrees C, rapidly rising short heat stimuli (4 degrees C s‐1, 2 s plateau) elicited vasodilatation at an average threshold of 39.4 degrees C. For slowly rising sustained heat stimuli (64 s duration) the average threshold was 39.6 degrees C (n.s.) Laser Doppler flowmetry revealed a rapid onset within about 4 s, a long duration of several minutes beyond the end of the stimulus, and a rapid spread of vasodilatation to remote skin areas. These characteristics are typical for vasodilatation by an axon reflex of nociceptive afferents. 3. Axon reflex thresholds matched the lower range of C fibre nociceptor heat thresholds. Thermal stimuli that were adjusted to elicit about half‐maximal phasic responses in warm fibres (steps from 30 to 35 degrees C), but were below the range of C fibre nociceptor thresholds, did not cause any vasodilatation. 4. Pain thresholds were higher than axon reflex thresholds for both rapidly and slowly rising heat stimuli and strongly depended on the stimulus pattern (40.1 degrees C for rapidly rising stimuli and > 43 degrees C for slowly rising stimuli). This observation is consistent with recent reports that the phasic response of nociceptive afferents is essential to overcome the summation requirements at central synapses. 5. In conclusion, axon reflex vasodilatation in response to heat stimuli in the hairy skin of humans is elicited by activation of heat‐sensitive nociceptors, even in the absence of a conscious perception of heat pain. The dissociation of pain and vasodilatation thresholds supports the concept of two operating ranges of primary nociceptive afferents. Warm fibres do not contribute to axon reflex vasodilatation in the hairy skin of the human forearm. Release of vasoactive peptides by nociceptive primary afferents may also contribute to local heat‐evoked vasodilatation at temperatures above 40 degrees C.
Muscarinic and nicotinic receptors raise intracellular Ca2+ levels in rat carotid body type I cells.
Authors: Dasso L L , Buckler K J , Vaughan-Jones R D
Published: December 2014

1. The effects of cholinergic agonists upon intracellular free Ca2+ levels ([Ca2+]i) have been studied in enzymically isolated rat carotid body single type I cells, using indo‐1. 2. Acetylcholine (ACh) dose‐dependently increased [Ca2+]i in 55% of cells studied (EC50 = 13 microM). These [Ca2+]i rises were partially inhibited by atropine or mecamylamine. 3. Specific nicotinic and muscarinic agonists also elevated [Ca2+]i in a dose‐dependent manner (nicotine, EC50 = 15 microM; methacholine, EC50 = 20 microM). 4. While the majority of the ACh‐sensitive cells responded to both classes of cholinergic agonist, 29% responded exclusively to nicotinic stimulation and 9% responded exclusively to muscarinic stimulation. 5. In the presence of nicotinic agonists, Ca2+i responses were transient. In the presence of muscarinic agonists, Ca2+i responses consisted of an initial rise, which then declined to a lower plateau level. 6. Nicotinic responses were rapidly abolished in Ca(2+)‐free medium, suggesting that they are dependent on Ca2+ influx. 7. The plateau component of the muscarinic‐activated response was also abolished in Ca(2+)‐free conditions. The rapid initial [Ca2+]i rise, however, could still be evoked after several minutes in Ca(2+)‐free medium. Muscarine also increased Mn2+ quenching of intracellular fura‐2 fluorescence. These data suggest that the full muscarinic response depends on both Ca2+ release from intracellular stores and Ca2+o influx. 8. The results indicate that, in rat carotid body type I cells, both nicotinic and muscarinic acetylcholine receptors increase [Ca2+]i, but achieve this via different mechanisms. ACh may therefore play a role in carotid body function by modulating Ca2+i in the chemosensory type I cells.
Evidence for uncoupling of oxygen and glucose utilization during neuronal activation in rat striatum.
Authors: Lowry J P , Fillenz M
Published: December 2014

1. Changes in regional cerebral blood flow (rCBF), tissue oxygen and extracellular glucose were measured during neuronal activation, using implanted electrodes in the striatum of freely moving rats. 2. There was a parallel increase in rCBF and oxygen in response to neuronal activation. 3. During the neuronal activation there was a decrease in extracellular glucose; following neuronal activation there was a slow rise in extracellular glucose which took 30 min to return to basal levels. 4. The implications of the different time courses of these changes are discussed.
The role of inward Na(+)‐Ca2+ exchange current in the ferret ventricular action potential.
Authors: Janvier N C , Harrison S M , Boyett M R
Published: December 2014

1. Inward Na(+)‐Ca2+ exchange current (iNaCa) was either blocked in ferret ventricular cells by replacing extracellular Na+ with Li+ or substantially reduced by the almost complete elimination of the Ca2+ transient by buffering intracellular Ca2+ with the acetoxymethyl ester form of BAPTA (BAPTA AM). 2. During square wave voltage clamp pulses to 0 mV, replacing extracellular Na+ with Li+ or buffering intracellular Ca2+ with BAPTA AM resulted in the loss of a transient inward current. This current was increased by the application of isoprenaline (expected to increase the underlying Ca2+ transient) and displayed the voltage‐dependent characteristics of inward iNaCa. 3. Replacing extracellular Na+ with Li+ or buffering intracellular Ca2+ caused a significant shortening of the action potential (at ‐65 mV, 44 +/‐ 2% with Li+ and 20 +/‐ 2% with BAPTA AM). The shortening can be explained by changes in iNaCa. 4. The action potential clamp technique was used to measure the BAPTA‐sensitive current (putative iNaCa) and the Ca2+ current (ica; measured using nifedipine) during the action potential. Under control conditions, the inward BAPTA‐sensitive current makes approximately the same contribution as iCa during much of the action potential plateau. These results suggest an important role for inward iNaCa in the ferret ventricular action potential.
Intracortical facilitation and inhibition after transcranial magnetic stimulation in conscious humans.
Authors: Nakamura H , Kitagawa H , Kawaguchi Y , Tsuji H
Published: December 2014

1. Changes in excitability of the motor cortex induced by a transcranial magnetic stimulation (TMS) were examined by simultaneous recording of the evoked corticospinal volley and the compound surface electromyographic (EMG) response in the biceps brachii following paired‐pulse TMS in five conscious subjects. The effects of a varying interstimulus interval (ISI) and a conditioning stimulus intensity were also investigated. 2. A submotor threshold conditioning stimulus inhibited the test responses at ISIs of 2‐5 ms. A supramotor threshold conditioning stimulus inhibited the test responses at ISIs of 100‐200 ms. Both of these inhibitions were prominent in late I waves. 3. There was a facilitation of the test responses at an ISI of 25 ms that was prominent in late I waves. The facilitation evoked by the supramotor threshold conditioning stimulus was more prominent than that evoked by the submotor threshold conditioning stimulus. 4. It is concluded that single TMS induced the triphasic changes of the motor cortex excitability in conscious humans that resulted in changes in EMG responses following paired TMS.
Conditional dendritic oscillators in a lobster mechanoreceptor neurone.
Authors: Combes D , Simmers J , Moulins M
Published: December 2014

1. Intra‐ and extracellular recordings were made from in vitro preparations of the lobster (Homarus gammarus) stomatogastric nervous system to study the nature and origin of pacemaker‐like activity in a primary mechanoreceptor neurone, the anterior gastric receptor (AGR), whose two bilateral stretch‐sensitive dendrites ramify in the tendon of powerstroke muscle GM1 of the gastric mill system. 2. Although the AGR is known to be autoactive, we report here that in 20% of our preparations, rather than autogenic tonic discharge, the receptor fired spontaneously in discrete bursts comprising three to ten action potentials and repeating at cycle frequencies of 0.5‐2.5 Hz in the absence of mechanical stimulation. Intrasomatic recordings revealed that such rhythmic bursting was driven by slow oscillations in membrane potential, the frequency of which was voltage sensitive and dependent upon the level of stretch applied to the receptor terminals of the AGR. 3. Autoactive bursting of the AGR originated from an endogenous oscillatory mechanism in the sensory dendrites themselves, since (i) during both steady, repetitive firing and bursting, somatic and axonal impulses were always preceded 1:1 by dendritic action potentials, (ii) hyperpolarizing the AGR cell body to block triggering of axonal impulses revealed attenuated somatic spikes that continued to originate from the two peripheral dendrites, (iii) the timing of burst firing could be phase reset by brief electrical stimulation of either dendrite, and (iv) spontaneous bursting continued to be expressed by an AGR dendrite after physical isolation from the GM1 muscle and the stomatogastric nervous system. 4. Although a given AGR in vitro could switch spontaneously from dendritic bursting to tonic firing and vice versa, exogenous application of micromolar (or less) concentrations of the neuropeptide F1 (TNRNFLRFamide) to the dendritic membrane could rapidly and reversibly switch the receptor firing pattern from repetitive firing to the bursting mode. Exposure of the somatic and axonal membrane of the AGR to F1 was without effect, as were applications of other neuroactive substances such as serotonin, octopamine and proctolin. 5. We conclude that, as for many oscillatory neurones of the central nervous system, the intrinsic activity pattern of this peripheral sensory neurone may be dynamically conferred by extrinsic modulatory influences, presumably according to computational demands. Moreover, the ability of the AGR to behave as an endogenous burster imparts considerable integrative complexity since, in this activity mode, sensory coding not only occurs through the frequency modulation of on‐going dendritic bursts but also via changes in the duration of individual bursts and their inherent spike frequencies.
Pore mutations in Shaker K+ channels distinguish between the sites of tetraethylammonium blockade and C‐type inactivation.
Authors: Molina A , Castellano A G , López-Barneo J
Published: December 2014

1. We have studied the effect of external K+ and tetraethylammonium (TEA) on several mutants of Shaker B K+ channels with amino acid substitutions in the pore which alter TEA affinity and the rate of C‐type inactivation. In all channels studied high external K+ makes C‐type inactivation slower. 2. In the wild‐type channel, TEA blockade is voltage dependent and produces slowing of the inactivation time course. However, in the double mutant channel (T449Y, D447E) TEA blockade, although of higher affinity, is voltage independent and does not affect the rate of C‐type inactivation. 3. Mutants with a charged amino acid at position 449 (T449K and T449E) are resistant to TEA block. In these channels, C‐type inactivation is also unaffected by TEA. 4. These results indicate that the sites where TEA blocks and competes with C‐type inactivation can be segregated. To modulate inactivation, TEA must enter deeply into the channel mouth. These results suggest that C‐type inactivation is not due to a large molecular rearrangement in the outer channel vestibule, but it is essentially produced by a conformational change restricted to a local site in the pore.
Cytoplasmic calcium buffers in intact human red cells.
Authors: Tiffert T , Lew V L
Published: December 2014

1. Precise knowledge of the cytoplasmic Ca2+ buffering behaviour in intact human red cells is essential for the characterization of their [Ca2+]i‐dependent functions. This was investigated by using a refined method and experimental protocols which allowed continuity in the estimates of [Ca2+]i, from nanomolar to millimolar concentrations, in the presence and absence of external Ca2+ chelators. 2. The study was carried out in human red cells whose plasma membrane Ca2+ pump was inhibited either by depleting the cells of ATP or by adding vanadate to the cell suspension. Cytoplasmic Ca2+ buffering was analysed from plots of total cell calcium content vs. ionized cytoplasmic Ca2+ concentration ([CaT]i vs. [Ca2+]i) obtained from measurements of the equilibrium distribution of 45Ca2+ at different external Ca2+ concentrations ([Ca2+]o), in conditions known to clamp cell volume and pH. The equilibrium distribution of 45Ca2+ was induced by the divalent cation ionophore A23187. 3. The results showed the following. (i) The known red cell Ca2+ buffer represented by alpha, with a large capacity and low Ca2+ affinity, was the main cytoplasmic Ca2+ binding agent. (ii) The value of alpha was remarkably constant; the means for each of four donors ranged from 0.33 to 0.35, with a combined value of all independent measurements of 0.34 +/‐ 0.01 (mean +/‐ S.E.M., n = 16). This contrasts with the variability previously reported. (iii) There was an additional Ca2+ buffering complex with a low capacity (approximately 80 micromol (340 g Hb)(‐1)) and intermediate Ca2+ affinity (apparent dissociation constant, K(D,app) approximately 4‐50 microM) whose possible identity is discussed. (iv) The cell content of putative Ca2+ buffers with submicromolar Ca2+ dissociation constants was below the detection limit of the methods used here (less than 2 micromol (340 g Hb)(‐1)). 4. Vanadate (1 mM) inhibited the Vmax of the Ca2+ pump in inosine‐fed cells by 99.7%. The cytoplasmic Ca2+ buffering behaviour in these cells was similar to that found in ATP‐depleted cells.
Excitability changes in human cutaneous afferents induced by prolonged repetitive axonal activity.
Authors: Kiernan M C , Mogyoros I , Hales J P , Gracies J M , Burke D
Published: December 2014

1. The present study was undertaken to document the excitability changes produced by prolonged high‐frequency trains of impulses in cutaneous afferents of six human subjects. 2. Trains of supramaximal stimuli at 200 Hz for 2 min or less produced a prolonged depression in excitability, consistent with activation of the electrogenic Na+‐K+ pump. Trains of longer duration resulted in an initial period of hyperexcitability which, with 10 min trains, was associated with the sensation of paraesthesiae in all subjects. This transient hyperexcitability gradually gave way to a long‐lasting period of hypoexcitability. 3. The excitability changes were reproducible, and were accompanied by corresponding changes in supernormality, refractoriness, strength‐duration time constant and rheobase current, suggesting that the changes in axonal excitability reflected a change in membrane potential. 4. The transient increase in excitability that follows tetanic trains of 10 min had qualitatively similar effects on cutaneous axons as ischaemia or application of a depolarizing current. The post‐tetanic changes in the supernormal period of sensory axons were those expected from the changes in excitability, without evidence of a gross distortion in its time course, as has been previously demonstrated in a hyperstimulated human motor axon. 5. It is concluded that the post‐tetanic hyperexcitability of human sensory axons is probably driven by increased K+ accumulation in the restricted diffusion space under the myelin sheath, much as in motor axons, the differences in behaviour of sensory and motor axons being explicable by greater inward rectification in sensory axons.
Dual effects of tetracaine on spontaneous calcium release in rat ventricular myocytes.
Authors: Györke S , Lukyanenko V , Györke I
Published: December 2014

1. Confocal microfluorometry was used to study the effects of tetracaine on spontaneous Ca2+ release from the sarcoplasmic reticulum (SR) in isolated rat ventricular myocytes. 2. At low concentrations (0.25‐1.25 mM), tetracaine caused an initial inhibition of spontaneous release events (Ca2+ sparks) and Ca2+ waves, which was followed by a gradual increase in Ca2+ release activity. The frequency and magnitude of sparks were first decreased and then increased with respect to control levels. At high concentrations (> 1.25 mM), tetracaine abolished all forms of spontaneous release. 3. Exposure of the myocytes to tetracaine resulted in a gradual increase in the SR Ca2+ load as indexed by changes in the magnitude of caffeine‐induced Ca2+ transients. 4. In cardiac SR Ca(2+)‐release channels incorporated into lipid bilayers, tetracaine (> 0.25 mM) induced a steady inhibition of channel activity. Addition of millimolar Ca2+ to the luminal side of the channel caused an increase in channel open probability under control conditions as well as in the presence of various concentrations of tetracaine. 5. We conclude that the primary effect of tetracaine on SR Ca(2+)‐release channels is inhibition of channel activity both in vitro and in situ. The ability of tetracaine to reduce spark magnitude suggests that these events are not due to activation of single channels or non‐reducible clusters of channels and, therefore, supports the multichannel origin of sparks. We propose that the paradoxical late potentiation of release by submaximal concentrations of tetracaine is caused by a gradual increase in SR Ca2+ load and subsequent activation of the Ca(2+)‐release channels by Ca2+ inside the SR.
Ca(2+)‐activated K+ channels in rat otic ganglion cells: role of Ca2+ entry via Ca2+ channels and nicotinic receptors.
Authors: Callister R J , Keast J R , Sah P
Published: December 2014

1. Intracellular recordings were made from neurones in the rat otic ganglion in vitro in order to investigate their morphological, physiological and synaptic properties. We took advantage of the simple structure of these cells to test for a possible role of calcium influx via nicotinic acetylcholine receptors during synaptic transmission. 2. Cells filled with biocytin comprised a homogeneous population with ovoid somata and sparse dendritic trees. Neurones had resting membrane potentials of ‐53 +/‐ 0.7 mV (n = 69), input resistances of 112 +/‐ 7 M omega, and membrane time constants of 14 +/‐ 0.9 ms (n = 60). Upon depolarization, all cells fired overshooting action potentials which were followed by an apamin‐sensitive after‐hyperpolarization (AHP). In response to a prolonged current injection, all neurones fired tonically. 3. The repolarization phase of action potentials had a calcium component which was mediated by N‐type calcium channels. Application of omega‐conotoxin abolished both the repolarizing hump and the after‐hyperpolarization suggesting that calcium influx via N‐type channels activates SK‐type calcium‐activated potassium channels which underlie the AHP. 4. The majority (70%) of neurones received innervation from a single preganglionic fibre which generated a suprathreshold excitatory postsynaptic potential mediated by nicotinic acetylcholine receptors. The other 30% of neurones also had one or more subthreshold nicotinic inputs. 5. Calcium influx via synaptic nicotinic receptors contributed to the AHP current, indicating that this calcium has access to the calcium‐activated potassium channels and therefore plays a role in regulating cell excitability.
Human body‐segment tilts induced by galvanic stimulation: a vestibularly driven balance protection mechanism.
Authors: Day B L , Séverac Cauquil A , Bartolomei L , Pastor M A , Lyon I N
Published: December 2014

1. We have studied the effects of changes in posture on the motor response to galvanic vestibular stimulation (GVS). The purpose of the experiments was to investigate whether the function of the GVS‐evoked response is to stabilize the body or the head in space. Subjects faced forwards with eyes closed standing with various stance widths and sitting. In all cases the GVS‐evoked response consisted of a sway of the body towards the anodal ear. 2. In the first set of experiments the response was measured from changes in (i) electromyographic activity of hip and ankle muscles, (ii) the lateral ground reaction force, and (iii) lateral motion of the body at the level of the neck (C7). For all measurements the response became smaller as the feet were placed further apart. 3. In the second set of experiments we measured the GVS‐evoked tilts of the head, torso and pelvis. The basic response consisted of a tilt in space (anodal ear down) of all three segments. The head tilted more than the trunk and the trunk tilted more than the pelvis producing a leaning and bending of the body towards the anodal ear. This change in posture was sustained for the duration of the stimulus. 4. The tilt of all three segments was reduced by increasing the stance width. This was due to a reduction in evoked tilt of the pelvis, the bending of the upper body remaining relatively unchanged. Changing from a standing to a sitting posture produced additional reductions in tilt by reducing the degree of upper body bending. 5. The results indicate that the response is organized to stabilize the body rather than the head in space. We suggest that GVS produces a vestibular input akin to that experienced on an inclined support surface and that the function of the response is to counter any threat to balance by keeping the centre of mass of the body within safe limits.
Axial Wall Conduction in Pulsating Laminar Flow in a Microtube
Authors: Mishra Parthasarathi , Moharana Manoj Kumar
Published: December 2014

A two-dimensional numerical analysis is carried out to understand the effect of pulsation on the axial wall conduction in simultaneously developing single phase laminar flow in a microtube with constant heat flux boundary condition imposed on its outer surface and while the cross-sectional solid faces exposed to the surrounding are kept adiabatic. Water is used as the working fluid and enters the microtube at 300K with a slug velocity that varying with time sinusoidally, thus causing pulsating flows in the microtube. The inlet velocity thus consists of a fixed component and a fluctuating component which varies sinusoidally with time. For this simulation conductivity ratio is considered at a wide range (ksf 2.26–703) while the thickness ratio (δsf), amplitude (A), and flow rate (Re) remain constant. To understand effect of pulsation, frequency of oscillation (f) is changed by taking four different Womersley numbers (1.414, 2, 2.45, and 3.163). Based on the numerical simulation, it is concluded that for a particular pulsation frequency (Wo) there exists an optimum value of ksf at which overall Nusselt number (Nu) is maximum. Effect of pulsation frequency on heat transfer is found to be very small. Heat transfer is found to be increasing at lower thermal conductive microtube wall material (or ksf) while it is decreasing at higher ksf compared to steady flow in microtube. Existing studies do indicate that pulsation (i) increases heat transfer (ii) decreases heat transfer, or (iii) no effect. The researchers actually failed to observe the present overall trend as none of the existing studies considered a widely varying thermal conductive wall material.
How do plasma-generated OH radicals react with biofilm components? Insights from atomic scale simulations
Authors: Khosravian Narjes , Bogaerts Annemie , Huygh Stijn , Yusupov Maksudbek , Neyts Erik C.
Published: December 2014

The application of nonthermal atmospheric pressure plasma is emerging as an alternative and efficient technique for the inactivation of bacterial biofilms. In this study, reactive molecular dynamics simulations were used to examine the reaction mechanisms of hydroxyl radicals, as key reactive oxygen plasma species in biological systems, with several organic molecules (i.e., alkane, alcohol, carboxylic acid, and amine), as prototypical components of biomolecules in the biofilm. Our results demonstrate that organic molecules containing hydroxyl and carboxyl groups may act as trapping agents for the OH radicals. Moreover, the impact of OH radicals on N-acetyl-glucosamine, as constituent component of staphylococcus epidermidis biofilms, was investigated. The results show how impacts of OH radicals lead to hydrogen abstraction and subsequent molecular damage. This study thus provides new data on the reaction mechanisms of plasma species, and particularly the OH radicals, with fundamental components of bacterial biofilms.
Abiotrophia defectiva endocarditis
Authors: Pinkney Jodian Amor , Nagassar Rajeev Peeyush , Roye-Green Karen Judith , Ferguson Trevor
Published: December 2014

A previously healthy 27-year-old Jamaican man presented to the University Hospital of the West Indies with recurrent joint pain, remitting and relapsing fever, and shortness of breath. He was subsequently found to haveAbiotrophia defectivaendocarditis. This was the first time this organism had been isolated at our institution. Despite culture directed antibiotics, his clinical course was quite severe with mitral regurgitation and congestive cardiac failure requiring mitral valve replacement. He recovered well postoperatively and is currently being followed at our outpatient cardiology clinic. This report highlights the severe presentation and often poor outcome associated withA. defectivaendocarditis and stresses that the outcome may be improved by early and appropriate surgical intervention.