bluuebunny/crossref_metadata_2025 huggingface dataset:
The actions of presynaptic snake toxins on membrane currents of mouse motor nerve terminals.
Authors: Dreyer F , Penner R
Published: December 2014

1. The m. triangularis sterni of the mouse was used to investigate the actions of dendrotoxin, beta‐bungarotoxin, crotoxin, taipoxin, bee venom phospholipase A2, aprotinin and apamin on presynaptic currents which flow inside the perineural sheath of nerve bundles upon nerve stimulation. 2. Neither the fast K+ current (IK,f) nor the Ca2+‐dependent K+ current IK(Ca) (unmasked after blockade of IK,f by 3,4‐diaminopyridine) was affected by the neurotoxins and drugs mentioned. 3. Inhibition of both IK,f and IK(Ca) by tetraethylammonium (30 mM) prolonged presynaptic depolarization owing to Ca2+ influx through fast and slow Ca2+ channels. Additional application of dendrotoxin, beta‐bungarotoxin, crotoxin or taipoxin in the nanomolar range caused further prolongation of Ca2+ influx, presumably due to blockade of slowly activating K+ current (IK,s). Onset of toxin effects was immediate and could not be reversed by washing for 60 min. 4. Similar prolongation of slow Ca2+ current was effected by 3,4‐diaminopyridine, whereas addition of apamin, aprotinin or phospholipase A2 left the signals unchanged. 5. These data indicate that facilitatory actions of dendrotoxin, beta‐bungarotoxin, taipoxin and crotoxin are mediated by an increase of Ca2+ entry into nerve terminals. The actions of these toxins are discussed in terms of a blockade of presynaptic K+ channels with slow activation kinetics.
Regulation of ion permeability in frog brain venules. Significance of calcium, cyclic nucleotides and protein kinase C.
Authors: Olesen S P
Published: December 2014

1. The effect on ionic permeability of frog brain endothelium of various second messengers was studied by a technique based on continuous recording of the electrical resistance of the venular endothelium in vivo. 2. Augmentation of the cytosolic Ca2+ concentration in endothelial cells induced with the ionophores ETH 1001 and A23187 increased ion permeability significantly as reflected in the reduced electrical resistance. 3. The electrical resistance fell reversibly within 1‐2 s after administration of Ca2+‐activating agents. The maximal effect was a reduction to about 0.70 times the pre‐experimental resistance value. The resistance decrease was similar to that induced by several inflammatory mediators (Olesen & Crone, 1986). 4. Administration of the following agents did not change the electrical wall resistance: 8‐bromo‐cyclic AMP, dibutyryl‐cyclic AMP, forskolin, 8‐bromo‐cyclic GMP, dibutyryl‐cyclic GMP, sodium nitroprusside, phorbol myristate acetate (a protein kinase C stimulator). Changes in cytosolic Mg2+ did not affect permeability. 5. Ca2+ may be an important cytosolic signal in the endothelial cell, acting as an intracellular mediator for several permeability‐augmenting substances.
Effect of albumin on the osmotic pressure exerted by myoglobin across capillary walls in frog mesentery.
Authors: Curry F E , Michel C C , Phillips M E
Published: December 2014

1. Individual capillaries in mesenteries of pithed frogs were perfused sequentially with two frog Ringer solutions containing myoglobin at a concentration of 70 mg/ml. The first perfusate solution contained bovine serum albumin at a concentration of 10 mg/ml. The second perfusate contained no albumin. The modified Landis micro‐occlusion technique (Michel, Mason, Curry & Tooke, 1974) was used to measure the capillary hydraulic conductivity and the effective osmotic pressure of the myoglobin solution across the capillary wall under conditions where the transcapillary concentration difference was established by steady‐state ultrafiltration. 2. In six capillaries the effective osmotic pressure of the myoglobin solution at 20‐22 degrees C was 15.9 +/‐ 2.2 (S.E. of mean) cmH2O when albumin was in the perfusate and 10.1 +/‐ 1.1 cmH2O after albumin was removed from the perfusate. 3. The hydraulic conductivity of the capillary wall increased from a mean value of 6.5 +/‐ 1.4 X 10(‐7) cm/(s cmH2O) when albumin was in the perfusate to 15.6 +/‐ 3.8 X 10(‐7) cm/(s cmH2O) during perfusion with Ringer solution containing myoglobin alone. 4. Control experiments to measure steady‐state filtration rates at pressures 10‐30 cmH2O were carried out to check the assumption in the method that the reduction in the measured osmotic pressure of myoglobin was the result of changes in the properties of the molecular sieve within the capillary wall and was not simply the result of solute accumulation on the tissue side of the capillary wall. 5. The measured reduction in the effective osmotic pressure of myoglobin when albumin was removed from the perfusate does not conform to the hypothesis (Crone, 1984) that the tight segment of the intercellular junction is the principal molecular filter for myoglobin in the wall of frog mesenteric capillaries. 6. Our results do conform to the hypothesis that a network of fibrous molecules, reinforced by adsorbed albumin, forms the principal molecular filter at the capillary wall in frog mesenteric capillaries.
Evidence supporting a role for endogenous vasopressin in fever suppression in the rat.
Authors: Cooper K E , Naylor A M , Veale W L
Published: December 2014

1. Infusion of human purified interleukin‐1 into a lateral cerebral ventricle of the rat evoked a rise in core temperature which was abolished by heating the interleukin‐1. 2. When the intracerebroventricular infusion of interleukin‐1 was preceded by a bilateral injection of saline into the ventral septal area, the resulting febrile response was not different from that induced by interleukin‐1 alone. However, when the vasopressin V1 antagonist, d(CH2)5Tyr(Me)AVP, was injected into the ventral septal area prior to interleukin‐1, a fever was evoked which was significantly greater in magnitude and duration. This enhancement of fever by the V1 antagonist was dose related. 3. Injection of either saline or the V1 antagonist into the ventral septal area, in the absence of interleukin‐1, did not evoke any consistent alteration in the core temperature of the rats. 4. The vasopressin V2 antagonist, d(CH2)5‐D‐ValVAVP, was injected into the ventral septal area to determine the effect of another vasopressin analogue on the fever evoked by interleukin‐1. The V2 antagonist did not alter the time course of interleukin‐1‐induced fever or alter core temperature in the afebrile rat. 5. These data are consistent with the hypothesis that endogenous vasopressin, released in the ventral septal area, may be involved in limiting fever. In addition, these results indicate that the central receptor mediating the antipyretic action of vasopressin may resemble the V1 subtype of peripheral vasopressin receptor.
Calcium‐dependent potassium conductance in guinea‐pig olfactory cortex neurones in vitro.
Authors: Constanti A , Sim J A
Published: December 2014

1. Guinea‐pig olfactory cortex neurones in vitro (23‐25 degrees C) were voltage clamped by means of a single‐micro‐electrode sample‐and‐hold technique. 2. Under current clamp at the resting potential (approximately ‐80 mV), brief depolarizing stimuli evoked trains of action potentials with little visible after‐potential. However, in 90% of recorded cells held at membrane potentials between ‐70 and ‐45 mV, depolarizing current pulses evoked a slow after‐hyperpolarization (a.h.p.) (approximately 8 mV) lasting several seconds and accompanied by an increase in input conductance. 3. The outward membrane current underlying the a.h.p. was revealed either by switching rapidly to voltage clamp at the end of a spike train ('hybrid' clamp) or by applying brief depolarizing commands from potentials between ‐60 to ‐45 mV. The tail current showed a distinct rising phase (time to peak approximately 1 s) and exponential decay (tau approximately 3 s) and was suppressed by removal of external Ca2+, or adding Co2+ (1‐2 mM), Cd2+ (200 microM) or Mg2+ (6 mM). The a.h.p. current reversal potential was ‐96 mV in 3 mM‐K+ medium. 4. Low concentrations (1‐2 microM) of muscarine, carbachol, oxotremorine or the muscarinic ganglion stimulant, McN‐A‐343 (1‐10 microM) reduced the a.h.p. current and leak conductance and induced a steady inward current, without affecting M‐current (IM) relaxations. IM inhibition generally required higher (greater than 10 microM) agonist concentrations, although oxotremorine remained ineffective at up to 50 microM. 5. The a.h.p. current was reduced by noradrenaline and tetraethylammonium (TEA), but not by apamin or tubocurarine. Apart from TEA, these agents had no effect on IM. 6. Addition of tetrodotoxin (TTX, 1 microM) or removing external Na+ depressed the a.h.p. current amplitude recorded under voltage clamp. The residual tail current could be further reduced by adding Cd2+ or muscarinic agonists. 7. Repolarizing tail currents induced following positive voltage commands consisted mainly of IM and slow a.h.p. current with little evidence of a 'fast' Ca2+‐activated K+ current (IC). 8. It is concluded that the slow a.h.p. current that underlies the post‐burst after‐hyperpolarization of olfactory neurones, is a Ca2+‐dependent K+ current distinct from IM. It is suggested that the cholinergic modulation of this current (rather than IM) may provide a more subtle control of cell excitability in cortical neurones.
The effect of membrane potential on the mammalian sodium‐potassium pump reconstituted into phospholipid vesicles.
Authors: Goldshlegger R , Karlish S J , Rephaeli A , Stein W D
Published: December 2014

1. We have studied effects of electrical diffusion potentials on active Na+‐K+ exchange in phospholipid vesicles reconstituted with pig kidney Na+, K+‐ATPase. 2. Diffusion potentials, negative inside, were established using outwardly directed K+ gradients plus valinomycin or Li+ gradients plus a Li+ ionophore, AS701. Measurement of fluorescence changes of the carbocyanine dye DiS‐C3‐(5) showed that the ionophores generated potentials of the expected orientation and of sufficient stability for their effects on active transport to be assessed. Measurement of rates of passive 22Na+ fluxes, over a wide range of diffusion potentials, were consistent with the quantitative predictions of the constant‐field flux equation. This result demonstrates that values of diffusion potentials calculated from the Nernst or constant‐field equation are accurate. 3. In some conditions, the inside‐negative potential (‐130 to ‐180 mV) accelerated the rate of ATP‐dependent Na+‐K+ exchange on inside‐out‐oriented pumps, compared to 'control' without the ionophores. Reduction in the size of the diffusion potentials by addition to the medium of Li+ with AS701 or Cs+ with the valinomycin progressively annulled the acceleratory effects, consistent with these being true effects of a change in membrane potentials. 4. At saturating cytoplasmic Na+ and ATP concentrations, the diffusion potential accelerated ATP‐dependent Na+‐K+ exchange by up to about 30% compared to control but this effect disappeared at rate‐limiting ATP concentrations (approximately 1 microM). 5. Using prior knowledge of rate‐limiting steps, we interpret this finding to mean that the conformational transition E2(2K)‐‐‐‐E12K associated with transport of two K+ ions is voltage insensitive while E1P(3Na)‐‐‐‐E2P3Na associated with transport of three Na+ ions is voltage sensitive. The simplest explanation is that the net charge in the transport domain of the protein when no ions, 2K+ or 3Na+ are bound is ‐2, 0 and +1 respectively. 6. The accelerating effect of the negative‐inside diffusion potential on Na+‐K+ exchange is greater at limitingly low cytoplasmic Na+ concentrations than at saturating cytoplasmic Na+ concentrations. Cytoplasmic Na+ activation curves show that the diffusion potential increases the apparent cytoplasmic Na+ affinity and reduces the sigmoidicity of cytoplasmic Na+ activation. 7. A kinetic analysis reveals that this effect on apparent affinity is due to an increase in intrinsic Na+ binding and occurs in addition to the effect on a transport rate constant.(ABSTRACT TRUNCATED AT 400 WORDS)
Purinergic inhibition in the small intestinal myenteric plexus of the guinea‐pig.
Authors: Palmer J M , Wood J D , Zafirov D H
Published: December 2014

1. The actions of adenosine on electrical behaviour of myenteric neurones were investigated with intracellular recording methods in guinea‐pig small intestine. 2. The actions of adenosine were: membrane hyperpolarization, decreased input resistance, enhancement of post‐spike hyperpolarizing potentials and suppression of excitability. These effects were observed exclusively in AH/type 2 myenteric neurones. 3. The presence of adenosine in the micromolar range of concentrations prevented or suppressed excitatory responses to forskolin. It also aborted the effects of forskolin when added in combination with this activator of adenylate cyclase. 4. Adenosine (100 microM) did not affect the excitatory actions of intracellularly injected cyclic AMP, membrane‐permeant analogues of cyclic AMP, inhibitors of cyclic nucleotide phosphodiesterase or elevation of Mg2+ and reduction of Ca2+ in the bathing medium. 5. The results suggest that the mechanism of the inhibitory action of adenosine is suppression of the catalytic activity of adenylate cyclase and consequent reduction of intraneuronal levels of cyclic AMP.
Transduction of aminergic and peptidergic signals in enteric neurones of the guinea‐pig.
Authors: Palmer J M , Wood J D , Zafirov D H
Published: December 2014

1. The biogenic amines 5‐hydroxytryptamine (5‐HT) and histamine, and the peptides bombesin, gastrin‐releasing peptide (GRP), vasoactive intestinal peptide (VIP), cholecystokinin (CCK), substance P and calcitonin gene‐related peptide (CGRP) each mimicked slow synaptic excitation (slow e.p.s.p.) when applied to myenteric neurones of the guinea‐pig small intestine. 2. Stimulation of the catalytic activity of adenylate cyclase by forskolin and intraneuronal elevation of cyclic 3',5'‐adenosine monophosphate (cyclic AMP) also mimicked the slow e.p.s.p. and the actions of the aminergic and peptidergic messengers. 3. Adenosine prevented stimulation of adenylate cyclase by forskolin and abolished the slow e.p.s.p.‐like actions of forskolin. 4. Exposure of the neurones to adenosine prior to or during application of bombesin, GRP, VIP, CCK or histamine blocked the actions of these substances. 5. Pre‐treatment with adenosine did not suppress the slow e.p.s.p.‐like actions of substance P, CGRP or 5‐HT. 6. The results suggest that signal transduction for bombesin, GRP, VIP, CCK and histamine involves stimulation of adenylate cyclase and second messenger function of cyclic AMP. Transduction mechanisms for 5‐HT, substance P and CGRP appear not to involve second messenger function of cyclic AMP.
Activation of cat motor units by paired stimuli at short intervals.
Authors: Horcholle-Bossavit G , Jami L , Petit J , Scott J J
Published: December 2014

1. In adult cats, paired stimulations at short intervals were applied in ventral root filaments to single motor axons innervating the peroneus tertius muscle. Paired impulses were recorded from the muscle nerve simultaneously with the electrical and mechanical responses of the muscle portion of the motor unit (muscle unit). The interstimulus interval was gradually reduced in order to determine the minimum compatible with a full activation of the muscle unit by the second impulse. 2. For motor units of all physiological types, this minimum stimulus interval was the shortest interval allowing initiation and conduction of two impulses in the axon, that is, the absolute refractory period for conduction. Its duration ranged between 0.58 and 0.88 ms, displaying no correlation with the axonal conduction velocity. 3. The amount of tension enhancement produced by paired stimulations at the shortest interval varied with the type of the motor unit: it was largest for fast‐fatigable units, intermediate for fast‐resistant units and smallest for slow units. 4. Paired impulses elicited by paired stimulations at the shortest possible interval arrived near the muscle at a longer interval because the second impulse was conducted at a slower velocity. The minimum interval between arrival of impulses at the muscle depended on conduction velocity and on conduction distance. 5. In motor axons to peroneus tertius, paired impulses leaving the spinal cord at a mean interval of 0.78 ms arrived near the muscle separated by a mean interval of 1.90 ms. Since such an interval always allowed full activation of the muscle unit by the second impulse, this interval is longer than the refractory period of motor units in this muscle.
Inhibitory interactions in the human vision system revealed in pattern‐evoked potentials.
Authors: Burr D C , Morrone M C
Published: December 2014

1. Visual evoked potentials (v.e.p.s) were recorded from human adults to investigate orientation‐specific neural interactions. The stimuli were the sum of two gratings, sinusoidally modulated in space and time at different frequencies. Recordings were made for one grating (test) alone, and with another superimposed grating (mask), oriented parallel or orthogonal to the test. The amplitude and phase of the v.e.p.s at twice the test modulation frequency (second harmonic) was measured as a function of test contrast to produce contrast‐response curves. 2. Orthogonal masks attenuated considerably the amplitude of v.e.p.s. The attenuation at any given contrast was approximately proportional, or multiplicative, lowering the slope of the contrast‐response curve, without affecting significantly the extrapolated threshold. Parallel masks also attenuated v.e.p. amplitudes but in a different way, leaving the slope of the contrast‐response curves unchanged, while elevating threshold. 3. The attenuation by orthogonal masks occurred over a wide range of test spatial frequencies, from 0.8 to 8 cycles/deg. For any given test spatial frequency, the most effective masks were those of spatial frequency similar to or lower than the test. Masks of spatial frequency 1.5 octaves higher than the test did not attenuate v.e.p. amplitudes. 4. The mask temporal frequency for maximal attenuation of v.e.p. amplitude was around 12 Hz, with stationary masks having little effect. 5. Under most conditions, the phase of the second harmonic of the v.e.p., increased with increasing contrast (phase advance). Superimposition of a parallel mask abolished phase advance, while orthogonal masks increased it. 6. Comparisons with single cortical unit and evoked potential recordings in cats suggest that the attenuation by orthogonal masks reflects intracortical inhibitory interactions between cell populations of different orientation preference.
Multiple actions of substance P that regulate the functional properties of acetylcholine receptors of clonal rat PC12 cells.
Authors: Boyd N D , Leeman S E
Published: December 2014

1. The effects of substance P (SP) on each of the kinetic components of reversible desensitization (measured at 4 degrees C) and also on irreversible deactivation (measured at 22 degrees C) of the nicotinic acetylcholine receptor on PC12 cells were examined by 22Na+ influx measurements of the functional state of the receptor. 2. In the absence of agonists, SP converts the acetylcholine receptors in a time‐ and concentration‐dependent manner, to a state that is not responsive to agonist. Upon removal of the peptide, this effect was reversible and the kinetics of the recovery of the permeability response were analysed to provide further characterization of the non‐responsive state. Following exposure of cells to SP (10 microM) for 3 or more min, recovery was by a first‐order process (time constant, t1/2 = 2.1 min), the same value, within experimental error, as that observed for recovery measured after the initial rapid phase of agonist‐mediated desensitization. 3. In the presence of agonist, SP caused a strong enhancement of both the rate and extent of agonist‐mediated desensitization. This effect was observed even at concentrations of peptide which produced only a small extent of desensitization when incubated alone. For 500 microM‐carbamylcholine, the equilibrium level of desensitization (approximately 85% loss of the permeability response) was achieved at 4 degrees C in about 20 min by a biphasic process, while in the presence of 1.0 microM‐SP, complete (100%) desensitization occurred by a single rapid exponential phase characterized by a t1/2 of 20 s. 4. The concentration of carbamylcholine required to produce half‐maximal desensitization at equilibrium, Kdes, was 94 microM and was reduced by 6‐fold in the presence of 0.3 microM‐SP. 5. A mechanistic model is presented in which the receptor is viewed as existing in a dynamic conformational equilibrium between an activatable state Rc and the initial desensitized state Rd. It is proposed that SP binds preferentially to the Rd state and thus can allosterically (1) stabilize the receptor in the absence of agonist in that state, and (2) enhance, in an even lower concentration range, both the rate and extent of agonist‐mediated stabilization of the receptor in the Rd state. 6. The second, slower component of agonist‐mediated desensitization is, in contrast, inhibited by SP. This desensitization step appears to involve a covalent modification of the initial desensitized state (Rd) and is dependent on Ca2+. SP may exert this inhibitory effect by limiting the access of Ca2+ to an intracellular site of action.(ABSTRACT TRUNCATED AT 400 WORDS)
The labile respiratory activity of ribcage muscles of the rat during sleep.
Authors: Megirian D , Pollard M J , Sherrey J H
Published: December 2014

1. Sleep‐waking states of chronically implanted rats were identified polygraphically while recording the integrated electromyogram (e.m.g.) of extrinsic (scalenus medius and levator costae) and intrinsic (external and internal interosseous intercostal and parasternal) muscles of the thoracic cage. Rats breathed air, air enriched in CO2 (5%) or air deficient in O2 (10% O2 in N2) and were free to adopt any desired posture. 2. In non‐rapid eye movement (non‐r.e.m.) sleep, the scalenus medius and intercostal muscles of the cephalic spaces were always inspiratory; intercostal muscles of the mid‐thoracic spaces were commonly expiratory while the more caudal ones were only occasionally expiratory. Expiratory activity, when present in quiet wakefulness, extended for a variable period of time into non‐r.e.m. sleep and always disappeared in r.e.m. sleep regardless of the ribcage muscle under study. 3. Inspiratory activity, when present in non‐r.e.m. sleep, was unaffected, partially attenuated or abolished at entry into r.e.m. sleep. The peak integrated e.m.g. activity of ribcage muscles was measured as a function of posture, gas mixture breathed and ribcage site: (a) the greater the degree of curled‐up posture, the greater the respiratory activity of scalenus medius, an effect augmented by CO2 but depressed by hypoxia, and (b) the more caudally placed ribcage muscles exhibited respiratory activity which was essentially unaffected by posture and gas mixture inspired. 4. The presence or absence of tonic activity in ribcage respiratory muscles during non‐r.e.m. sleep was unrelated to posture. When tonic activity was present, it always disappeared in r.e.m. sleep. When expiratory activity was present in non‐r.e.m. sleep, it too always disappeared in r.e.m. sleep. Inspiratory activity present in non‐r.e.m. sleep was variably affected at entry into r.e.m. sleep; it was unchanged, partially attenuated or abolished. 5. It is concluded that thoracic cage muscles exhibit marked variability in their respiratory activity depending on posture, sleep‐waking states and gas mixture breathed. It is postulated that the presence of tonic and/or expiratory activity in ribcage muscles during non‐r.e.m. sleep reflects an increase in functional residual capacity (F.R.C.).
Predictive velocity estimation in the pursuit reflex response to pseudo‐random and step displacement stimuli in man.
Authors: Barnes G R , Donnelly S F , Eason R D
Published: December 2014

1. Eye movements have been recorded in man in response to various forms of continuous and discontinuous target motions in the horizontal plane in an attempt to establish the mechanisms of prediction in the pursuit reflex. 2. In an initial experiment the target motion was composed of four sinusoids, each of peak velocity +/‐ 3.3 deg/s. The three lowest frequencies (0.11, 0.24 and 0.37 Hz) remained constant whereas the highest frequency (F4) was varied from 0.39 to 2.08 Hz. When F4 was 0.39 Hz, all frequency components had a high level of eye velocity gain (mean 0.92) but as F4 was increased there was a significant (P less than 0.001) decline in gain for all three low frequencies which reached a minimum (mean 0.53) when F4 was 1.56 Hz. However, the gain for F4 always remained at a high level, comparable to that evoked by a discrete frequency sinusoid of the same frequency. 3. When the highest‐frequency sinusoid was replaced by a square wave of identical amplitude a similar decline in gain for the low frequencies was observed. Eye velocity exhibited a quasi‐sinusoidal modulation at the frequency of the square wave even though the rapid steps did not constitute a suitable stimulus to the visual velocity feed‐back mechanisms. 4. When only two sinusoids were mixed to form the pursuit stimulus a similar break‐down in gain of the lower‐frequency component was observed which reached a minimum (mean gain 0.58) when F2 was between 1 and 2 Hz. This implies that the predictability of stimulus motion is dependent, not on the complexity of the stimulus, but on its highest‐frequency component. 5. Presentation of square‐wave target displacements alone confirmed that smooth eye movements could be evoked by such a stimulus. Eye velocity was at a maximum between 1.0 and 1.5 Hz and was predictive of ensuing target displacement. Responses to staircase step sequences of varying duration indicated that prediction was based on an assessment of the duration of the preceding sequence. 6. Tachistoscopic presentation of targets during low‐frequency sinusoidal oscillation indicated that illumination of the target for very short periods (10‐320 ms) as few as two times per cycle during minimum velocity phases enhanced the perception of continuous movement. A predictive eye movement was evoked with a high level of peak velocity which then decayed until the subsequent exposure of the target.(ABSTRACT TRUNCATED AT 400 WORDS)
Tetrodotoxin‐resistant sodium current of rat nodose neurones: monovalent cation selectivity and divalent cation block.
Authors: Ikeda S R , Schofield G G
Published: December 2014

1. Monovalent cation selectivity and divalent cation sensitivity of the tetrodotoxin (TTX)‐resistant Na+ current in dissociated adult rat nodose ganglion neurones were investigated using the whole‐cell patch‐clamp technique. 2. The TTX‐resistant Na+ current was isolated using ion substitution and pharmacological agents. Under these conditions, the current reversal potential shifted 52 mV per tenfold change in external [Na+]. 3. Inorganic and organic monovalent cation permeability ratios (Px/PNa) were determined from changes in reversal potential and the Goldman‐Hodgkin‐Katz equation. The Px/PNa values determined by the former method were HONH3+, 1.38; Li+, 1.00; H2NNH3+, 0.66; NH4+, 0.28; CH3NH3+, less than 0.13; K+, less than 0.13; Rb+, less than 0.12; Cs+, less than 0.10; (CH3)4N+, less than 0.10. The values determined by either method agreed within 10%. 4. The effects of Cd2+, Co2+, Mn2+ and Ni2+ on the TTX‐resistant Na+ current were analysed from peak‐conductance values. These ions shifted the activation of the current to more positive potentials and decreased the maximal conductance. At 3 mM concentrations, Cd2+, Ni2+, Co2+ and Mn2+ decreased the maximal conductance 64.6, 50.7, 25.0 and 20.3%, respectively. 5. The results indicate that: (a) the monovalent cation selectivity of the TTX‐resistant Na+ current is similar to that of the TTX‐sensitive Na+ current in other tissues; and (b) the TTX‐resistant Na+ current is less sensitive to divalent cations than the Ca2+ current in these neurones. These observations suggest that the structure determining the monovalent cation permeability of the TTX‐resistant Na+ current is similar to that of the TTX‐sensitive Na+ current in other tissues, and that the channels carrying the TTX‐resistant Na+ current are distinct from those responsible for the Ca2+ current.
Heterotopic activation of A delta and C fibres triggers inhibition of trigeminal and spinal convergent neurones in the rat.
Authors: Bouhassira D , Le Bars D , Villanueva L
Published: December 2014

1. Extracellular recordings were made from fourteen non‐noxious only and nineteen convergent neurones in trigeminal nucleus caudalis of halothane‐anaesthetized rats. All the neurones studied were excited by the continuous micro‐electrophoretic ejection of an excitatory amino acid, DL‐homocysteic acid (DLH), with mean currents of 38.0 +/‐ 7.2 and 39.8 + 6.5 nA producing steady discharges of 35.0 +/‐ 3.3 and 31.8 +/‐ 1.3 spikes/s from the non‐noxious only and convergent neurones respectively. 2. The repeated percutaneous application (100 trials; 0.66 Hz) of single square‐wave stimuli (10 mA; 2 ms) to the tail always induced a biphasic depression of the activity of the convergent, but never of the non‐noxious only, neurones. Both the early and late components of this inhibition occurred at shorter latencies when the base rather than the tip of the tail was stimulated. Differences in latencies from the two sites of stimulation (100 mm apart) were used to estimate the conduction velocities of the peripheral fibres which were triggering the inhibitions. 3. The cumulated results showed that, for the onset of the earlier component of the inhibition, the mean difference between the latencies from the two sites of stimulation was 13.6 +/‐ 1.9 ms, corresponding to a peripheral conduction velocity of 7.3 +/‐ 0.3 m/s, which is in the A delta‐fibre range. For the onset of the late component of inhibition, the mean difference was 147.7 +/‐ 14.9 ms, corresponding to a peripheral conduction velocity of 0.68 +/‐ 0.07 m/s, which is in the C‐fibre range. 4. When currents of different intensities were applied percutaneously to the two stimulation sites, the thresholds for obtaining the A delta component were in the range 0.25‐0.5 mA whereas the C component appeared with currents 1‐2 mA. A clear relationship between current intensity and magnitude of inhibition was observed in the 0.25‐2 mA range for the A delta component and in the 1‐5 mA range for the C component. 5. In an additional series of experiments recordings were made from eleven convergent neurones in the dorsal horn of the lumbar spinal cord. By using essentially the same experimental procedure the effects of repetitive application (100 trials, 0.66 Hz) of percutaneous electrical stimuli (1 or 10 mA, 2 ms) applied to the muzzle, were studied on the steady discharges (42.3 +/‐ 5.4 spikes/s) induced by DLH. The application of the 10 mA stimuli induced a biphasic depression of activity, whereas only an early component was observed following 1 mA stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Single calcium‐activated potassium channels recorded from cultured rat sympathetic neurones.
Authors: Smart T G
Published: December 2014

1. The properties of single Ca2+‐activated K+ channels in cultured rat superior cervical ganglionic neurones were studied in cell‐attached and excised patches using the patch‐clamp technique. 2. In cell‐attached patches using an external K+ concentration ([K+]o) of 150 mM, approximately equal to the internal [K+], the channel slope conductance was approximately 200 pS and independent of membrane voltage between ‐50 and +50 mV. Using [K+]o of 4.7 mM (providing a near physiological K+ gradient), the I‐V relationship was non‐linear with a slope conductance of approximately 120 pS at 0 mV. 3. The channel was selective for K+ over Cs+ and Na+ which were impermeant from either side of the membrane. Both Na+ and Cs+ also blocked the movement of K+ through the channel. Cs+ was active on either side of the membrane, whereas Na+ apparently blocked the channel only when applied to the cytoplasmic side. 4. The channel was activated by increasing the Ca2+ concentration on the inside of the membrane ([Ca2+]i). The channel was virtually inactive when [Ca2+]i = 0.01 microM. Depolarizing the patch at a constant [Ca2+]i usually further increased the opening probability. 5. The gating properties of the channel were studied using cell‐attached patches. At potentials more negative than the resting membrane potential, the open‐time distribution was described by a single exponential. On depolarization, two exponentials were required. The closed‐time distribution was fitted by three exponentials. 6. Depolarization of the patch caused the long mean open lifetime to increase whilst the short mean open and closed lifetimes were unaffected. Both the intermediate and long mean closed lifetimes decreased with depolarization from ‐60 to +60 mV. 7. In cell‐attached patches, the long mean open lifetimes were usually smaller than those observed in excised patches at depolarized potentials (greater than 0 mV). 8. A fourth closed state, possibly representing an inactivated form of the channel, was infrequently observed. A 50% substate of the full single‐channel current was also observed occasionally. This substate was always associated with openings to the full current state. 9. The channel was blockable by external tetraethylammonium (25 microM‐1 mM), Ba2+ (1‐10 mM), and quinine (10‐200 microM). External d‐tubocurarine (25‐100 microM) also blocked this IC channel. However it was insensitive to apamin (100‐300 nM), muscarine (10 microM) and 4‐aminopyridine (1‐3 mM). The channel was also blocked by internal tetraethylammonium (5‐10 mM) or Ba2+ (0.3‐1 mM).(ABSTRACT TRUNCATED AT 400 WORDS)
Heterogeneity of amino acid transport in horse erythrocytes: a detailed kinetic analysis of inherited transport variation.
Authors: Fincham D A , Mason D K , Paterson J Y , Young J D
Published: December 2014

1. Thoroughbred horses were divisible into five distinct amino acid transport subgroups on the basis of their erythrocyte permeability to L‐alanine, measured uptake rates ranging from 5 to 625 mumol l cells‐1 h‐1 (0.2 mM‐extracellular L‐alanine, 37 degrees C). 2. Erythrocytes from animals belonging to the lowest L‐alanine permeability subgroup (5‐15 mumol l cells‐1 h‐1) (transport‐deficient type) exhibited slow nonsaturable transport of this amino acid. In contrast, cells from horses of the four transport‐positive subgroups possessed additional high‐affinity (apparent L‐alanine Km (Michaelis constant) congruent to 0.3 mM) and/or low‐affinity (apparent L‐alanine Km congruent to 13 mM) Na+‐independent transport routes selective for L‐neutral amino acids of intermediate size. The two transporters, designated systems asc1 and asc2, respectively, also possessed a significant affinity for dibasic amino acids. 3. Amino acid transport activity in horse erythrocytes behaved as if controlled by three co‐dominant alleles (s, h and l), where s is a silent allele, and h and l code for the functional presence of systems asc1 and asc2, respectively. 4. At physiological temperature, system asc1 operated preferentially in an exchange mode. In contrast, system asc2 did not participate in exchange reactions at 37 degrees C, but did exhibit significant trans‐acceleration at 25 degrees C. 5. Reduction of the incubation temperature also resulted in dramatic decreases in apparent Km and Vmax for L‐alanine uptake by system asc2, whereas the effects of temperature on system asc1 were much less marked. At 5 degrees C the two transporters exhibited equivalent kinetic constants for L‐alanine influx. L‐Alanine uptake by transport‐deficient cells was relatively insensitive to temperature. Influx by this route may represent the ground‐state permeability of the lipid bilayer. 6. The effects of low temperature on system asc2 suggest a preferential impairment of the mobility of the unloaded carrier relative to that of the loaded transporter. Similarly, the different kinetic properties of systems asc1 and asc2 at physiological temperature are attributed to a difference in the mobilities of the empty carriers, this difference being minimized at 5 degrees C.
Activation patterns of embryonic chick lumbosacral motoneurones following large spinal cord reversals.
Authors: Vogel M W
Published: December 2014

1. Embryonic chick motoneurones were caused to innervate inappropriate hindlimb muscles by rotating the presumptive lumbosacral region of the neural tube in stage 15‐16 embryos which is prior to the outgrowth of motoneurone axons. 2. The activation patterns of motoneurones in control and spinal cord reversal embryos were analysed from electromyographic (e.m.g.) recordings of stage 36 limb muscles during evoked movement sequences in an isolated spinal cord‐limb preparation. Histograms representing the frequency of activation were constructed for each muscle. The muscle's pattern of activation was classified as flexor‐like or extensor‐like and compared to the activation patterns of control muscles. 3. A series of control operations was performed in which the prospective lumbosacral region of the neural tube was removed and replaced in its original orientation. Muscles in these embryos were innervated by their normal motoneurone pools and they were activated normally, indicating that the neural tube operation per se does not alter the activation pattern of motoneurones. Furthermore, some muscles (twelve out of sixty‐one) in spinal cord reversal embryos had normal activation patterns and appeared to be innervated by their original motoneurones. Based on these results and the result of a previous study (Landmesser & O'Donovan, 1984 b), it is concluded that motoneurones in reversed spinal cords are activated in a manner appropriate for their original identity. 4. The majority of muscles (thirty‐three out of sixty‐one) in large spinal cord reversal embryos were activated during an appropriate phase of the kicking cycle. Of the remaining muscles, 16% were activated inappropriately (i.e. extensor muscles were activated as flexors, and vice versa), and 30% had a novel 'mixed' flexor‐ and extensor‐like activation pattern. However, the activation pattern of most muscles differed markedly from that of any other control muscles regardless of whether the muscle was activated appropriately or inappropriately as a flexor or extensor. The abnormal activation patterns are a likely consequence of the diffuse distribution of inappropriate motoneurones projecting to foreign muscles in embryos with large spinal cord reversals. Since it is likely that motoneurones are still activated according to their original identity, the activation patterns of individual foreign motor units projecting to a muscle sum in e.m.g. recordings to produce a novel abnormal activation pattern.(ABSTRACT TRUNCATED AT 400 WORDS)
Action of noradrenaline on single smooth muscle cells freshly dispersed from the rat anococcygeus muscle.
Authors: Byrne N G , Large W A
Published: December 2014

1. Membrane responses were recorded using a standard patch pipette technique in isolated cells freshly dispersed from the rat anococcygeus muscle. Using the whole‐cell mode of recording, the ionophoretic application of noradrenaline evoked depolarization (current clamp) and inward current (voltage clamp) at membrane potentials of ‐50 to ‐60 mV. 2. The inward current to noradrenaline was reversibly blocked by low concentrations of phentolamine indicating that the response is mediated by alpha‐adrenoceptors. The inward current was associated with a conductance increase. 3. The ionic mechanism of the inward current was investigated in potassium‐free solutions. Alteration of the chloride equilibrium potential produced similar changes in the reversal potential of the noradrenaline‐induced current and it is concluded that noradrenaline opens chloride‐selective channels. 4. The noradrenaline‐activated chord conductance was increased by depolarization. From a holding potential of ‐50 mV depolarizing voltage steps in the presence of noradrenaline produced relaxations and the time constants of these relaxations at ‐50 and +30 mV were respectively 89 and 166 ms. 5. The calcium ionophore A23187 and caffeine applied in the bathing solution also induced an increase in chloride conductance. 6. It is concluded that in isolated cells of the rat anococcygeus muscle the depolarization to noradrenaline is mediated by an increase in membrane chloride conductance.
Assessing changes in presynaptic inhibition of I a fibres: a study in man and the cat.
Authors: Hultborn H , Meunier S , Morin C , Pierrot‐Deseilligny E
Published: December 2014

1. A method to assess changes in presynaptic inhibition of I a afferent terminals in man is proposed. The soleus H reflex was facilitated by a heteronymous I a volley from quadriceps and the amount of reflex facilitation was used to estimate the size of the conditioning I a excitatory post‐synaptic potential (e.p.s.p.). It is argued that the size of this e.p.s.p. as measured by the resulting amount of reflex facilitation reflects the amount of presynaptic inhibition on the corresponding I a fibres. A decrease in the reflex facilitation may then be ascribed to an increase in presynaptic inhibition of the I a fibres mediating the conditioning volley. 2. That the heteronymous I a facilitation from quadriceps to soleus is caused by a purely monosynaptic e.p.s.p. is a prerequisite for the validity of the method. Experimental evidence is therefore given in an Appendix that in man the earliest part (first 0.5 ms) of this heteronymous I a facilitation is mediated through a monosynaptic pathway. Evidence is also given that this earliest facilitation is not yet contaminated by any polysynaptic effects from I a or I b afferents. 3. The validity of the method was established in animal experiments in which presynaptic inhibition of I a fibres and post‐synaptic events in motoneurones could be assessed by direct tests. It was found that the amount of test reflex facilitation produced by a conditioning I a volley was decreased when I a fibres were subjected to presynaptic inhibition but remained unchanged when the motoneurone pool in which the test reflex was elicited received pure post‐synaptic inhibition. 4. In man, presynaptic inhibition of I a fibres was evoked by a short‐lasting (three shocks at 200 Hz) vibration applied to the tibialis anterior tendon. Such a vibratory burst reduced the efficiency of the heteronymous I a volley in facilitating the soleus H reflex. By contrast, during a pure post‐synaptic inhibition of soleus motoneurones the efficiency of the conditioning volley in facilitating the test reflex remained unchanged. It is therefore argued that the amount of heteronymous I a facilitation can indeed be used to assess the amount of ongoing presynaptic inhibition exerted onto heteronymous I a fibres from the quadriceps muscle to soleus motoneurones. 5. The short‐lasting tibialis anterior vibration used here evoked a long‐lasting (300‐500 ms) depression of soleus and quadriceps H reflexes.(ABSTRACT TRUNCATED AT 400 WORDS)
Spectral sensitivity of cones of the monkey Macaca fascicularis.
Authors: Baylor D A , Nunn B J , Schnapf J L
Published: December 2014

1. Spectral sensitivities of cones in the retina of cynomolgus monkeys were determined by recording photocurrents from single outer segments with a suction electrode. 2. The amplitude and shape of the response to a flash depended upon the number of photons absorbed but not the wave‐length, so that the 'Principle of Univariance' was obeyed. 3. Spectra were obtained from five 'blue', twenty 'green', and sixteen 'red' cones. The wave‐lengths of maximum sensitivity were approximately 430, 531 and 561 nm, respectively. 4. The spectra of the three types of cones had similar shapes when plotted on a log wave number scale, and were fitted by an empirical expression. 5. There was no evidence for the existence of subclasses of cones with different spectral sensitivities. Within a class, the positions of the individual spectra on the wave‐length axis showed a standard deviation of less than 1.5 nm. 6. Psychophysical results on human colour matching (Stiles & Burch, 1955; Stiles & Burch, 1959) were well predicted from the spectral sensitivities of the monkey cones. After correction for pre‐retinal absorption and pigment self‐screening, the spectra of the red and green cones matched the respective pi 5 and pi 4 mechanisms of Stiles (1953, 1959).
Reflex excitability of human soleus motoneurones during voluntary shortening or lengthening contractions.
Authors: Romanò C , Schieppati M
Published: December 2014

1. We investigated the possibility that increase or decrease in the monosynaptic reflex excitability of the soleus muscle in man might play a role in matching the muscle mechanical output to the voluntary command aimed at performing isotonic contractions or relaxations, at various velocities. 2. Rectified and integrated electromyographic activity (e.m.g.) and the H reflex of soleus were measured during plantar flexions against a constant load (shortening contractions) or dorsal flexions resisting the load (lengthening contraction), performed without activation of pretibial muscles. 3. At the same ankle joint angle, integrated e.m.g. was larger during shortening contractions than during lengthening contractions. During shortening contractions, integrated e.m.g. increased as a function of the velocity of plantar flexion. During lengthening contractions, integrated e.m.g. decreased as a function of dorsal flexion and angular velocity and nearly disappeared in the last part of the most rapid lengthening contractions. 4. During shortening contractions, the H reflex increased beyond the extent expected for the level of e.m.g. activity; during lengthening contractions, reduction of the H reflex below control values at rest occurred in spite of background e.m.g. activity. 5. When the level of e.m.g. activity was kept constant, the above changes in H reflex were larger in both directions as a function of the velocity of the movement. 6. Passive rotation in the dorsal direction contributed to the inhibition observed during lengthening contractions. 7. It is suggested that these changes in the excitability of the H reflex, probably presynaptic in origin, serve the purpose of appropriately modulating the rate and extent of motoneurone recruitment during shortening and lengthening contractions. This allows the foot to follow a constant‐velocity path in spite of the perturbing effects of the spindle afferent inputs and of the muscle characteristics described by the force‐‐length and force‐‐velocity diagrams.
The effects of post‐exercise glucose and alanine ingestion on plasma carnitine and ketosis in humans.
Authors: Carlin J I , Olson E B , Peters H A , Reddan W G
Published: December 2014

1. Several studies have hypothesized that alanine decreases plasma ketone body levels by increasing availability of oxaloacetate, thus allowing acetyl groups to enter the tricarboxylic acid cycle and releasing co‐enzyme A (CoA). 2. Four, fasted adult males exercised at 50% of their maximal oxygen consumption for 1.5 h, then ingested 100 g of either glucose or alanine 2 h into recovery. 3. Post‐exercise ketosis had developed at 2 h into recovery, as shown by a significantly elevated concentration of beta‐hydroxybutyrate in the plasma. At this time plasma free fatty acids were elevated above resting levels while plasma free carnitine concentrations had fallen below resting values. 4. After either alanine or glucose ingestion beta‐hydroxybutyrate concentrations fell to the same extent. After the alanine load free carnitine increased above that seen in the glucose trial. Following either alanine or glucose ingestion free fatty acid levels fell; they remained at resting levels in the alanine trial but decreased below rest in the glucose trial. 5. We assume that plasma carnitine concentrations largely reflect the hepatic carnitine pools; therefore, elevations in the plasma free carnitine are probably the result of an increased utilization of acetyl CoA. The significant elevation in plasma free carnitine concentration found after alanine ingestion is consistent with the hypothesis that alanine increases the oxidation of acetyl CoA by providing oxaloacetate for the tricarboxylic acid cycle.