bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversal of the cross‐bridge force‐generating transition by photogeneration of phosphate in rabbit psoas muscle fibres.
Authors: Dantzig J A , Goldman Y E , Millar N C , Lacktis J , Homsher E
Published: December 2014

1. Orthophosphate (P(i), 0.1‐2.0 mM) was photogenerated within the filament lattice of isometrically contracting glycerinated fibres of rabbit psoas muscle at 10 and 20 degrees C. The P(i) was produced by laser flash photolysis of the photolabile compound 1‐(2‐nitrophenyl)ethylphosphate (caged P(i)). Caged P(i) caused a depression of tension that was much smaller than that caused by P(i). 2. Photolysis of caged P(i) produced a decline in isometric force composed of four phases: phase I, a lag phase (e.g. 1‐4 ms at 10 degrees C) during which force did not change; phase II, an exponential decline by as much as 20% of the pre‐pulse force; phase III, a partial force recovery (0‐3% of the pre‐pulse force); and phase IV, a further slow (0.5‐3 s) decline to the steady value. Phases I, III and IV were largely independent of [P(i)] and are likely to be indirect effects caused by the caged P(i) photolysis. 3. Both the rate and amplitude of phase II depended markedly on [P(i)]. The amplitude of phase II was similar to the reduction of steady‐state force by P(i). The rate of phase II increased with increasing temperature and [P(i)]. At high [P(i)] the rate began to saturate, and approached limits of 123 s‐1 at 10 degrees C and 194 s‐1 at 20 degrees C. 4. The rate of phase II was independent of sarcomere overlap, while the amplitude was proportional to tension at partial filament overlap. A control experiment using caged ATP showed that phase II was not produced by the photolytic by‐products or the light pulse. The results suggest that phase II is associated with the force‐generating transition of the cross‐bridge cycle. 5. Sinusoidal length oscillations at 0.5 and 2 kHz were used to measure muscle stiffness during phase II. Stiffness declined in a single exponential phase, with the same time course as phase II of the tension transient. The change in stiffness was 83 +/‐ 6% (mean +/‐ S.E.M., n = 10, 0.5 kHz) of the change in tension when both signals were normalized to their pre‐flash values. 6. Analysis of the data shows that two steps are involved in force generation and P(i) release. The non‐force exerting AM‐ADP‐P(i) cross‐bridge state first isomerizes to form a force‐exerting cross‐bridge state (AM'‐ADP‐P(i)). P(i) is then released to form a second force‐generating state, AM'‐ADP.(ABSTRACT TRUNCATED AT 400 WORDS)
Two components of calcium‐activated potassium current in rat adrenal chromaffin cells.
Authors: Neely A , Lingle C J
Published: December 2014

1. The activation of calcium (Ca2+)‐dependent potassium (K+) currents in dissociated rat adrenal chromaffin cells was investigated using the dialysed cell recording technique. 2. Ca(2+)‐dependent K+ current was the major component of outward current at command potentials from ‐30 mV to about +50 mV. 3. Two components of Ca(2+)‐dependent outward current could be distinguished based on the voltage dependence of activation, the properties of tail currents following repolarization, and pharmacological properties. 4. One Ca(2+)‐dependent current was similar to an after‐hyperpolarization current (often termed IAHP) observed in other cell types. This current was largely blocked by 200 nM‐apamin or 200 microM‐curare, was associated with slow Ca(2+)‐dependent tail current, and exhibited little dependence on voltage. In cells with cytosolic Ca2+ buffered to 500 nM‐1 microM, curare‐sensitive current accounted for most of the membrane current at potentials negative to about ‐40 mV. 5. A second component of Ca(2+)‐activated K+ current exhibited voltage‐dependent activation, was completely blocked by 1 mM‐TEA, and turned off rapidly following repolarization. An unusual aspect of the TEA‐sensitive currents was that they appeared to inactivate under conditions of constant cytosolic Ca2+. 6. A novel observation during these experiments was a slow hump of outward current which appears to result from a non‐monotonic elevation in cytosolic Ca2+ during prolonged voltage jumps.
Effects of aortic pressure and vasoactive agents on the vascular resistance of the vasa vasorum in canine isolated thoracic aorta.
Authors: Ohhira A , Ohhashi T
Published: December 2014

1. We have developed a new preparation for continuously measuring changes in vascular resistance of the vasa vasorum of the canine isolated thoracic aorta perfused at a constant flow rate with Krebs‐bicarbonate solution. 2. An increase of more than 150 mmHg in aortic pressure caused a significant increase in the vascular resistance of the vasa vasorum. 3. 5‐Hydroxytryptamine (5‐HT), noradrenaline (NA), adrenaline and dopamine caused dose‐dependent increases in the vascular resistance of the vasa vasorum. The decreasing order of potency in the vasoconstrictor responses was as follows: 5‐HT >> NA = adrenaline >> dopamine. The 5‐HT‐ and adrenaline‐induced vasoconstrictor responses were inhibited by methysergide and by phentolamine plus propranolol, respectively. 4. Acetylcholine (ACh), isoprenaline (ISP), histamine (His), ATP, ADP and adenosine produced dose‐related decreases in the vascular resistance of aortic vasa vasorum perfused with the Krebs solution containing 10(‐5) M‐NA. The decreasing order of potency in the response was as follows: ACh = ISP > His >> adenosine = ATP = ADP. The ACh‐, ISP‐ and His‐induced vasodilator responses were antagonized by atropine, propranolol and famotidine, respectively. 5. The results suggest that the preparation described is useful for studying the regulation of vascular resistance of aortic vasa vasorum and that aortic pressure and vasoactive compounds may directly regulate the vascular resistance of the vasa vasorum in canine isolated thoracic aorta.
Transient hyperpolarization of non‐contracting muscle fibres in anaesthetized rats.
Authors: Kuiack S , McComas A
Published: December 2014

1. Following laminectomy, the L5 ventral roots of anaesthetized rats were split and approximately half of the nerve fibres were stimulated at 40 Hz. Resting membrane potentials were then measured in previously contracting and non‐contracting soleus muscle fibres. 2. In the non‐contracting soleus fibres there was a post‐tetanic increase in mean resting potential (from ‐82.2 +/‐ 7.1 (S.D.) to ‐91.6 +/‐ 8.7 mV) which was similar to that in contracting fibres (from ‐83.02 +/‐ 6.1 to ‐91.3 +/‐ 7.3 mV). In both types of fibres the hyperpolarizing responses (HRs) were evidently due to increased sodium pump activity since they could be abolished by the addition of ouabain (1 x 10(‐4) M) to the bathing fluid. 3. The beta‐adrenergic antagonist, propranolol, completely suppressed HRs in the non‐contracting fibres and produced moderate reductions in the contracting ones. The alpha‐adrenergic blocking agent, phentolamine, had no effect on the contracting fibres and only a modest, inhibitory, one on the non‐contracting fibres. 4. On the basis of the above drug actions it appeared that catecholamines were necessary for the full development of HRs in contracting and non‐contracting fibres; noradrenaline, released from intramuscular sympathetic nerve endings, may have been involved. 5. The increased sodium pump activity in the non‐contracting fibres would serve to moderate the rise in interstitial [K+] caused by K+ efflux from the contracting fibres. By preventing passive depolarization, due to the rise in interstitial [K+], the sodium pump would also maintain the availability of non‐contracting fibres for subsequent recruitment.
Equilibrium and kinetic study of glycine action on the N‐methyl‐D‐aspartate receptor in cultured mouse brain neurons.
Authors: Johnson J W , Ascher P
Published: December 2014

1. The characteristics of the activation of the N‐methyl‐D‐aspartate (NMDA) response by glycine were studied using whole‐cell and outside‐out patch clamp recording techniques. 2. Glycine concentration‐response (C‐R) curves were measured in the presence of 10 microM‐NMDA and fitted with the Hill equation modified to account for the response to NMDA observed in the absence of added glycine. The mean value of the apparent dissociation constant (KD) was 150 nM, and the mean value of the Hill coefficient (nH) was 1.1. When the KD was corrected for the concentration of contaminating glycine in nominally glycine‐free solutions, estimated assuming that there is no response in the absence of glycine, the value was 130 nM. 3. The question of how many glycine binding sites there are on each NMDA receptor‐channel complex was addressed by examining the curvature at the foot of the glycine C‐R curve. An equation that allowed estimation of both the concentration of contaminating glycine and of the value of nH was fitted to glycine C‐R data up to 50 nM. The mean value of nH was found to be 1.0, consistent with the idea that there is one glycine binding site. 4. The kinetics of the interaction of glycine with the NMDA receptor were measured by fitting single exponential curves to the current relaxation following a jump in glycine concentration in the presence of 10 microM‐NMDA. The plot of the inverse of the relaxation time constant as a function of glycine concentration after the concentration jump was linear. The association rate constant was estimated from these data as 1.2 x 10(7) M‐1 s‐1 and the dissociation rate as 1.0 s‐1. 5. Experiments were devised to allow the evaluation of the KD and dissociation rates of glycine in the absence of NMDA. They led to a value for KD of 80 nM, slightly but significantly lower than the value of 150 nM estimated in the presence of 10 microM‐NMDA. The glycine dissociation rate in the absence of NMDA was found to be 0.7 s‐1, not significantly different from that measured in the presence of 10 microM‐NMDA. 6. The results are consistent with a model of the NMDA receptor with a single glycine binding site. The characteristics of glycine binding are similar in the absence and the presence of 10 microM‐NMDA, although NMDA binding may cause a small increase in the glycine KD.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of maternal cold exposure on brown adipose tissue and thermogenesis in the neonatal lamb.
Authors: Symonds M E , Bryant M J , Clarke L , Darby C J , Lomax M A
Published: December 2014

1. This study examines the effect of chronic cold exposure during pregnancy, induced by winter shearing twin‐bearing ewes 4 weeks before predicted lambing date, on O2 consumption and CO2 production during non‐rapid‐eye‐movement (REM) sleep in lambs maintained for at least 1 h at warm (28‐18 degrees C) and cold (14‐5 degrees C) ambient temperatures at 1, 4, 14 and 30 days of age. This was combined with measurement of the thermogenic activity (GDP binding to uncoupling protein in mitochondrial preparations) of perirenal adipose tissue from lambs immediately after birth and at 33 days of age. 2. Lambs born from shorn (cold‐exposed) ewes were 15% heavier (P < 0.01) and possessed 21% (P < 0.01) more perirenal adipose tissue that contained 40% more protein and mitochondrial protein than unshorn (P < 0.05) controls. Total GDP binding in perirenal adipose tissue was 40% greater (P < 0.05) in lambs born from shorn ewes but there was no difference in lipid content of this tissue between the two groups. 3. At 1 day of age, lambs born from shorn ewes exhibited a 16% higher (P < 0.05) rate of O2 consumption (per kilogram bodyweight) at the warm temperature and a 40% greater metabolic response to the cold ambient temperature. All lambs born from shorn ewes responded to cold exposure without shivering (i.e. via non‐shivering thermogenesis) whilst shivering was measured in four out of seven lambs in the unshorn group. These differences had disappeared by 4 days of age as a result of a 25% increased (P < 0.01) rate of O2 consumption in the warm in lambs born from unshorn ewes and a 20% decrease (P < 0.05) in the response to the cold in lambs from shorn ewes. Shivering during cold exposure was measured in six out of nine lambs born from shorn ewes indicating a rapid alteration in thermoregulatory responses to cold during the first few days of life. 4. The levels of GDP binding and mitochondrial protein in perirenal adipose tissue fell by one‐third in both groups of lambs during the first 33 days of life whereas lipid content either increased or was unchanged. This indicated that brown adipose tissue (BAT) was developing the characteristics of white adipose tissue.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium current modulation in frog sympathetic neurones: L‐current is relatively insensitive to neurotransmitters.
Authors: Elmslie K S , Kammermeier P J , Jones S W
Published: December 2014

1. Neurotransmitters (noradrenaline, NA; chicken II luteinizing hormone‐releasing hormone, LHRH) and activators of G proteins (GTP‐gamma‐S and AlF3) partially inhibit calcium current in bullfrog sympathetic neruones. Activation of the remaining current is slowed and shifted to more positive voltages. 2. The N‐type calcium current appears to be the type modulated, since approximately 90% of peak current is blocked by omega‐conotoxin (omega CgTx) and modulation is not affected by nisoldipine. 3. Calcium current at relatively negative voltages (‐30 to ‐50 mV) is resistant to transmitter modulation. The current at such voltages is also resistant to omega CgTx, suggesting that it results from a different type of calcium channel. 4. The omega CgTx‐resistant current includes dihydropyridine (DHP)‐sensitive and DHP‐resistant components. The omega CgTx‐ and DHP‐resistant current is inhibited by transmitter agonist, but the DHP‐sensitive (L‐type) current is not. 5. In cells dialysed with a low concentration of calcium buffer (0.1 mM‐BAPTA), transmitters still inhibit N‐current incompletely. However, L‐current was partially inhibited (approximately 10%) by LHRH, NA and the muscarinic agonist oxotremorine‐M (OXO‐M).
Voltage‐dependent sodium and calcium currents in cultured parasympathetic neurones from rat intracardiac ganglia.
Authors: Xu Z J , Adams D J
Published: December 2014

1. Depolarization‐activated Na+ and Ca2+ currents underlying the rising phase of the action potential in mammalian parasympathetic ganglion cells were investigated in voltage‐clamped neurones dissociated from neonatal rat intracardiac ganglia and maintained in tissue culture. 2. A current component isolated by replacing intracellular K+ with Cs+ or arginine and adding 0.1 mM Cd2+ to the external solution was dependent on extracellular [Na+] and reversibly blocked in the presence of 300 nM tetrodotoxin (TTX). Peak amplitudes of Na+ currents elicited by step depolarization from a holding potential of ‐100 mV were 351 +/‐ 18 pA/pF (140 mM extracellular Na+). 3. The sodium current‐voltage (I‐V) curve exhibited a threshold for activation at ‐40 mV and reached a maximum at ‐10 mV. The Na+ conductance increased sigmoidally with increasing depolarization reaching half‐maximal activation at ‐25 mV, with a maximum slope corresponding to 7.5 mV per e‐fold change in conductance. 4. During a maintained depolarization, Na+ currents turned on and then decayed (inactivated) with an exponential time course. The time constant of inactivation was voltage dependent decreasing from 0.85 ms at ‐20 mV to 0.3 ms at +60 mV (23 degrees C). The steady‐state inactivation of the Na+ conductance was voltage‐dependent with half‐inactivation occurring at ‐61 mV and near‐complete inactivation at ‐20 mV. Recovery from inactivation also followed an exponential time course with a time constant that increased at depolarized membrane potentials. 5. A voltage‐ and Ca(2+)‐dependent current was isolated by replacement of intracellular K+ with either Cs+ or arginine and of extracellular Na+ with tetraethylammonium and the addition of TTX. Extracellular Ba2+ or Na+ (in the absence of external divalent cation) could substitute for Ca2+. Peak Ca2+ current increased with increasing extracellular [Ca2+] and above 10 mM (Kd approximately 4 mM) approached saturation. The peak Ca2+ current density was 45 +/‐ 4 pA/pF (2.5 mM‐extracellular Ca2+). 6. The Ca2+ I‐V relation exhibited a high threshold for activation (‐20 mV) and reached a maximum at +20 mV. Changing the holding potential from ‐100 to ‐40 mV did not alter the I‐V relationship. Peak Ca2+ conductance increased sigmoidally with increasing depolarization reaching half‐maximal activation at ‐4 mV, with a maximal slope of 4 mV per e‐fold change in Ca2+ conductance. 7. The kinetics of activation and inactivation of the Ca2+ current were voltage dependent and the time course of inactivation was fitted by the sum of two exponentials.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibitory synaptic currents in rat cerebellar Purkinje cells: modulation by postsynaptic depolarization.
Authors: Vincent P , Armstrong C M , Marty A
Published: December 2014

1. Synaptic currents were recorded in voltage‐clamped cerebellar Purkinje cells using the tight‐seal whole‐cell recording technique. Cells were dialysed with a CsCl solution and were held at ‐60 or ‐70 mV. Inhibitory interneurones (basket and stellate cells) were stimulated using an extracellular pipette positioned in the molecular layer. Blockers of excitatory glutamatergic synapses were included in the bath solution. 2. Evoked synaptic currents were observed after a latency of 3‐4 ms. The time course of synaptic currents could in most cases be fitted to a biexponential curve, with a rise time constant, tau on, of 1‐3 ms and a decay time constant, tau off, of 7‐13 ms. These currents were blocked by bicuculline. 3. The mean amplitude of evoked synaptic currents increased in discrete steps when the voltage applied to the stimulating pipette was increased. At each level, very prominent fluctuations of the amplitude were observed among trials. 4. Complex synaptic currents corresponding to repetitive activity of the presynaptic interneurone were occasionally observed, particularly with high intensity presynaptic stimulation. This repetitive activity could lead to bursts of synaptic currents lasting for several seconds. 5. Following a depolarizing voltage train in the postsynaptic Purkinje cell, the amplitude of evoked synaptic currents was first inhibited, and then potentiated. The inhibition was accompanied by a small but consistent increase in tau off and by no alteration in tau on. When using small intensity presynaptic stimuli, it was found that the probability of failures was greatly enhanced. The inhibitory phase lasted for about 1 min before giving way to potentiation. The potentiation returned to the control with a time to half‐decay of 12.9 +/‐ 0.9 min. 6. The present results give further evidence to a previously proposed hypothesis that the inhibition produced by Purkinje cell depolarization is mainly presynaptic. The longer lasting potentiation, on the other hand, has most probably a postsynaptic origin. Cerebellar Purkinje cells receive inhibitory GABAergic inputs from two classes of interneurones located in the molecular layer (reviewed in Palay & Chan‐Palay, 1974; Ito, 1984). Basket cells are closest to the Purkinje cell layer and address their inhibitory signal primarily to the soma and to the main dendrites. Stellate cells are more externally located and have contacts with the more distal part of the dendritic arborization of Purkinje cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanism of action of oxytocin in rat vagal neurones: induction of a sustained sodium‐dependent current.
Authors: Raggenbass M , Dreifuss J J
Published: December 2014

1. The mechanism of action of oxytocin on vagal neurones of the rat was studied using single‐electrode voltage‐clamp recordings from brainstem slices. The ionic basis of the oxytocin‐induced current was examined by changing the composition of the perfusion solution and by making use of channel blockers. 2. In neurones clamped at or near their resting potential, oxytocin generated a sustained, TTX‐insensitive inward current whose peak amplitude was concentration related. This current was detectable at 10 nM, was half‐maximal at about 100 nM and was maximal at micromolar concentrations of peptide. 3. The oxytocin current was inward over membrane potentials ranging from ‐110 to ‐20 mV and was voltage dependent, since it increased in magnitude as the membrane was depolarized from the resting potential toward less negative potentials. 4. Partial replacement of extracellular sodium by equimolar N‐methyl‐D‐glucamine reversibly attenuated or suppressed the oxytocin current. By contrast, substituting part of extracellular chloride or blocking calcium currents did not modify it. Increasing the transmembrane potassium gradient was also without effect and none of the potassium channel blockers TEA, 4‐amino pyridine (4‐AP), apamin, caesium or barium affected the oxytocin current. This current is thus at least in part carried by sodium. 5. The activation of the oxytocin current as a function of the membrane potential could be quantitatively simulated using a Boltzmann equation, suggesting that oxytocin acts by inducing the opening of a voltage‐dependent channel which can exist in either of two states, open or closed. 6. Lowering the extracellular calcium concentration from 2 to 0.1 mM, while keeping the magnesium concentration constant at 1 mM, enhanced the response to oxytocin. This low calcium‐induced potentiation of the oxytocin current was 1.4‐3‐fold and was reversible. 7. We conclude that oxytocin increases the excitability of vagal neurones by generating a persistent, voltage‐gated current which is sodium dependent, is insensitive to TTX and is modulated by divalent cations.
Membrane properties and synaptic responses of Golgi cells and stellate cells in the turtle cerebellum in vitro.
Authors: Midtgaard J
Published: December 2014

1. Intracellular recordings from anatomically identified Golgi cells and deep stellate cells were obtained in a slice preparation of the turtle cerebellar cortex. 2. Golgi cells and stellate cells had very similar firing patterns, which differed from those of Purkinje cells. In the interneurones, a short time constant and a high input resistance ensured a short response time. A pronounced spike after‐hyperpolarization (spike AHP) participated in the rapid repolarization following a depolarizing input. The active and passive membrane properties of the interneurones ensured a very tight temporal coupling between input and output. 3. TTX abolished both the action potentials and a subthreshold depolarizing response. The Na+ excitability was increased by addition of Mn2+ or Co2+ to block calcium channels, or by addition of potassium channel blockers. 4. Ca2+ spikes and a Ca2+ plateau could be evoked following addition of potassium channel blockers. A partly 4‐aminopyridine (4‐AP)‐sensitive transient hyperpolarization was found to control Ca2+ excitability in Golgi cells. It is suggested that this hyperpolarization is due to an A‐like conductance. 5. A strong anomalous rectification was activated just below spike threshold, and dominated the subthreshold membrane potential at time scales longer than ca 100 ms. The anomalous rectification was partly blocked by Cs+. 6. Temporal integration over time scales up to ca 25 s was provided by activity‐dependent adaptation in firing frequency and a long‐lasting after‐hyperpolarization (AHPL), which had both TTX‐sensitive, Ca(2+)‐independent, and Ca(2+)‐dependent components. 7. Spontaneous IPSPs and EPSPs were abundant. The IPSPs were abolished by bicuculline. EPSPs were easily evoked by parallel fibre stimulation, had a shorter time course than in Purkinje cells, and were suppressed by the spike AHP. 8. Due to a short response time and a relatively short overall time frame for temporal integration, cerebellar interneurones operate on a faster time scale than the Purkinje cells, the output neurones of the cerebellar cortex. 9. It is suggested that information from shared sources, e.g. the parallel fibres, is distributed onto dynamically different cellular populations based on differences in the intrinsic membrane properties of the postsynaptic neurones.
Ca(2+)‐activated and voltage‐gated K+ currents in smooth muscle cells isolated from human mesenteric arteries.
Authors: Smirnov S V , Aaronson P I
Published: December 2014

1. Smooth muscle cells were enzymatically isolated from arteries dissected from mesenteric fat removed from patients undergoing routine surgery. The whole‐cell patch clamp technique was used to characterize the potassium (K+) currents and passive electrical properties of these cells, using high‐K(+)‐containing pipette solutions with either 0.2 mM EGTA or 10 mM EGTA and 10 mM BAPTA. 2. Cell capacitance, which is proportional to membrane surface area, was normally distributed around a value of 46 pF, and independent of artery size between 0.4 and 3.6 mm. The mean membrane potential measured under current clamp was ‐44.1 +/‐ 1.9 mV (n = 52). 3. Cells dialysed with 0.2 mM EGTA in order to weakly buffer intracellular Ca2+ demonstrated a noisy outward current with an apparent threshold near ‐30 mV, upon which were superimposed spontaneous transient outward currents (STOCs). In the presence, but not the absence, of extracellular Ca2+, this current was potentiated if the holding potential was depolarized into the voltage range between ‐40 and +50 mV. This potentiation had a bell‐shaped potential dependency which reflected the activation of voltage‐gated Ca2+ channels in these cells. 4. The noisy current was blocked by externally applied tetraethylammonium (the dissociation constant, Kd = 0.85 mM), as were STOCs. This current was also reduced by about 40% by 8 nM charybdotoxin, and was transiently potentiated by 10 mM caffeine. The characteristics of this current therefore suggested that it was carried by large‐conductance Ca(2+)‐activated K+ channels. 5. Dialysis of human mesenteric arterial cells with 10 mM EGTA and 10 mM BATPA was not able to completely suppress the Ca(2+)‐activated current, and reduced by approximately 50% the amplitude of the outward current recorded at positive potentials. 6. Depolarization of strongly Ca(2+)‐buffered cells in the presence of 30 mM TEA to block Ca(2+)‐activated K+ channels revealed a residual outward current which had both transient and sustained components. These were blocked by 4‐aminopyridine (4‐AP) with a similar efficiency (Kd was 1.04 and 1.16 mM at +60 mV for transient and sustained current, respectively), but the voltage ranges over which they inactivated, and their rates of recovery from inactivation, were significantly different. 7. The transient and sustained currents had different sensitivities to external Ca2+ and Cd2+ ions. Ca2+ (5 mM) significantly reduced the amplitude and shifted the voltage dependency of inactivation of the transient but not the sustained component of the outward current. Cd2+ (0.2 mM) reduced the transient current by about 30% without affecting the sustained component amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)
Detection of slow movements imposed at the elbow during active flexion in man.
Authors: Taylor J L , McCloskey D I
Published: December 2014

1. Subjects' ability to detect movements imposed at the elbow during active flexion was measured. Movements of three different angular velocities (0.04, 0.4 and 4.4 deg/s) were applied to the arm while subjects maintained one of two force levels of active flexion. The threshold magnitudes for detection of the direction of imposed movement were found. 2. All thresholds were very small. At the lowest velocity of movement the average threshold was 0.13 deg and no subject had a threshold of greater than 0.3 deg. This contrasts with thresholds of over 2 deg measured in a previous study when the muscles about the joint were relaxed. Thresholds decreased further with increasing velocity of movement. 3. No difference was found between the two levels of contraction of the elbow flexors. However, extension (stretch of the contracting muscle) and flexion thresholds were calculated separately, and smaller extensions than flexions could be detected. 4. These findings indicate that conscious detection of imposed movements is greatly enhanced during active muscle contraction. Movements which cause unloading of the contracting agonist, as well as movements which result in stretch, are more easily detected than when the muscle is contracting. The discussion focuses on possible mechanisms for this enhancement.
A physiological study of vestibular and prepositus hypoglossi neurones projecting to the abducens nucleus in the alert cat.
Authors: Escudero M , de la Cruz R R , Delgado‐García J M
Published: December 2014

1. Vestibular and prepositus hypoglossi (PH) neurones projecting to the abducens (ABD) nucleus were recorded in the alert cat. Their discharge characteristics were analysed to ascertain the origin of the horizontal eye position signal present in ABD neurones. 2. Neurones were classified according to: their location with respect to the ABD nucleus; their antidromic activation from the ABD nucleus; the synaptic field potential they induced in the ABD nucleus with the spike‐triggered averaging technique; and their activity during spontaneous and vestibularly induced eye movements. 3. Vestibular neurones projecting to the ABD nucleus were located in the rostral medial vestibular nucleus. They were excitatory on the contralateral and inhibitory on the ipsilateral ABD neurones. Both types of premotor vestibular neurone showed a firing rate weakly related to eye position, increasing for eye fixations in the contralateral on‐direction, and decreasing with ipsilateral fixation. Position sensitivity during eye fixations was (means +/‐ S.D.) 1.8 +/‐ 0.9 spikes s‐1 deg‐1 for excitatory neurones and 2.2 +/‐ 1.3 spikes s‐1 deg‐1 for inhibitory neurones. Firing rate exhibited a high variability during eye fixations. Their responses during saccades in the off‐direction were characterized by a pause that, although less defined, was occasionally present during saccades in the on‐direction. Eye velocity sensitivity during spontaneous saccades in the on‐direction was 0.17 +/‐ 0.15 spikes s‐1 deg‐1 s‐1 for excitatory neurones and 0.15 +/‐ 0.07 spikes s‐1 deg‐1 s‐1 for inhibitory vestibular neurones. During sinusoidal head stimulation at 0.2 Hz, vestibular neurones showed a type I discharge rate with a phase lead over eye position of 86.0 +/‐ 14.1 deg for excitatory and 80.2 +/‐ 12.5 deg for inhibitory neurones. Position sensitivity during vestibular stimulation did not differ significantly from values obtained for spontaneous eye movements. However, the velocity sensitivity of premotor vestibular neurones during head rotation was significantly higher (1.6 +/‐ 0.2 spikes s‐1 deg‐1 s‐1 for excitatory and 1.5 +/‐ 0.3 spikes s‐1 deg‐1 s‐1 for inhibitory neurones) than during spontaneous eye movements. 4. PH neurones projecting to the ABD nucleus were located in the rostral one‐third of the nucleus. These neurones were excitatory on the ipsilateral and inhibitory on the contralateral ABD nucleus. Their firing rates were correlated mainly with eye position, increasing for abducting eye positions of the ipsilateral eye and decreasing with adduction movements.(ABSTRACT TRUNCATED AT 400 WORDS)
Comparison of ionic currents from interstitial cells and smooth muscle cells of canine colon.
Authors: Lee H K , Sanders K M
Published: December 2014

1. Voltage‐dependent ionic currents of isolated interstitial cells were characterized using the whole‐cell voltage clamp technique, and compared with currents recorded from circular muscle cells. Both cell types were isolated from the submucosal pacemaking region in the canine distal colon. 2. Upon depolarization, interstitial cells and smooth muscle cells generated transient inward, followed by slowly inactivating outward, currents. 3. After blocking inward current and much of the Ca(2+)‐dependent outward current, interstitial cells displayed voltage‐dependent outward current that rapidly activated, reached a peak, and then inactivated. This current was resistant to 4‐aminopyridine(4‐AP; 1 mM). Smooth muscle cells expressed a similar current but it was reduced by about 40% at a test potential of +20 mV by 4‐AP (1 mM). 4. The inactivation characteristics of the voltage‐dependent outward currents of interstitial cells and smooth muscle cells were compared. The outward current of interstitial cells inactivated at more negative potentials; half‐inactivation occurred at ‐53 mV, whereas half‐inactivation occurred at ‐20 mV in smooth muscle cells. 5. Inward currents were not strikingly different in the two cell types when dialysing pipettes were used. When the perforated patch technique (using Amphotericin‐B) was used, a negatively activating inward current was observed in interstitial cells that had a resolution threshold of ‐70 to ‐60 mV. This current peaked at ‐10 mV. Inward currents in smooth muscle cells were resolved at test potentials positive to ‐50 mV and peaked at 0 to +10 mV. 6. When interstitial cells were held at ‐40 mV, inward current could not be resolved with test depolarization negative to ‐30 mV. From this holding potential, peak amplitude was reduced by 85% with test depolarizations to ‐10 mV. Holding smooth muscle cells at ‐40 mV also reduced inward current, but the peak current in these cells was reduced by only 39% at 0 mV. 7. Ni2+ partially inhibited peak inward current in interstitial cells and abolished a ‘hump’ in the I‐V curve that occurred at negative potentials. In dialysed cells where this ‘hump’ was not apparent, addition of nifedipine unmasked a ‘hump’. The presence of both nifedipine and Ni2+ abolished inward current. 8. A portion of the inward current in smooth muscle cells was sustained and persisted for the duration of test pulses. Very little sustained inward current was observed in interstitial cells. 9. The time course of inactivation of inward current in interstitial cells was fitted with two exponentials.(ABSTRACT TRUNCATED AT 400 WORDS)
Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment.
Authors: Nielsen B , Hales J R , Strange S , Christensen N J , Warberg J , Saltin B
Published: December 2014

1. Heat acclimation was induced in eight subjects by asking them to exercise until exhaustion at 60% of maximum oxygen consumption rate (VO2) for 9‐12 consecutive days at an ambient temperature of 40 degrees C, with 10% relative humidity (RH). Five control subjects exercised similarly in a cool environment, 20 degrees C, for 90 min for 9‐12 days; of these, three were exposed to exercise at 40 degrees C on the first and last day. 2. Acclimation had occurred as seen by the increased average endurance from 48 min to 80 min, the lower rate of rise in the heart rate (HR) and core temperature and the increased sweating. 3. Cardiac output increased significantly from the first to the final heat exposure from 19.6 to 21.4 l min‐1; this was possibly due to an increased plasma volume and stroke volume. 4. The mechanism for the increased plasma volume may be an isosmotic volume expansion caused by influx of protein to the vascular compartment, and a sodium retention induced by a significant increase in aldosterone. 5. The exhaustion coincided with, or was elicited when, core temperature reached 39.7 +/‐ 0.15 degrees C; with progressing acclimation processes it took progressively longer to reach this level. However, at this point we found no reduction in cardiac output, muscle (leg) blood flow, no changes in substrate utilization or availability, and no recognized accumulated ‘fatigue’ substances. 6. It is concluded that the high core temperature per se, and not circulatory failure, is the critical factor for the exhaustion during exercise in heat stress.
Membrane properties and synaptic potentials of three types of neurone in rat lateral amygdala.
Authors: Sugita S , Tanaka E , North R A
Published: December 2014

1. Intracellular recordings were made from the lateral nucleus of the amygdala in tissue slices cut from rat brain and maintained in vitro. 2. Three types of neurones were distinguished according to the after‐potential that followed an action potential. Type 1 cells (44%, n = 225) had depolarizing after‐potentials, resulting from a calcium‐dependent chloride conductance. Type 2 cells (48%) had long‐lasting (> 250 ms) hyperpolarizing after‐potentials and type 3 cells (8%) had shorter hyperpolarizing after‐potentials. The average resting potentials of the three cell types were ‐78, ‐69 and ‐62 mV respectively. Intracellular labelling with biocytin showed that type 1 cells were pyramidal neurones; type 2 and type 3 cells were non‐pyramidal. 3. Experiments with receptor antagonists identified synaptic potentials mediated by excitatory amino acids and by GABA (acting at GABAA receptors) in all three cell types. A longer duration inhibitory synaptic potential resulting from activation of GABAB receptors was present in type 1 (pyramidal) and type 2 cells. 4. Cholecystokinin (100 nM to 1 microM) depolarized type 2 and type 3 cells but had no effect on type 1 (pyramidal) cells. Baclofen (1‐3 microM) hyperpolarized type 1 and type 2, but not type 3 cells. [Met5]enkephalin (1‐10 microM) hyperpolarized only type 2 cells. 5. It is concluded that the lateral nucleus of the amygdala contains pyramidal neurones and two types of non‐pyramidal neurone; these can be differentiated by membrane properties, synaptic inputs and sensitivities to transmitters.
The role of the motor cortex in the control of accuracy of locomotor movements in the cat.
Authors: Beloozerova I N , Sirota M G
Published: December 2014

1. The impulse activity of single neurones in the motor cortex (MC) was recorded extracellularly, using movable varnish‐insulated tungsten microelectrodes, in six adult, freely moving cats. Neuronal activity was recorded while the cats walked on a flat floor, as they stepped over a series of barriers, and as they walked on the flat rungs of a horizontal ladder. The mean discharge rate (mR) and the depth of frequency modulation (dM) in each cell were estimated over 10‐100 steps. 2. The activity of ninety‐eight MC cells (Including thirteen pyramidal tract neurones (PTNs)) was recorded during stepping over barriers 25 cm apart. The mR in 66% and the dM in 61% of these cells changed by more than 20% during locomotion with barriers compared to locomotion on the flat (an increase was more often the case). 3. The activity of nine cells was recorded during stepping over barriers 12 cm apart, and the activity of twenty‐seven cells (including five PTNs) during walking with barriers only 6 cm apart. The mR in 67% and in 59% of the cells, respectively, and the dM in 56% and in 67% of the cells, respectively, were greater in these locomotor tasks than during locomotion on the flat. 4. The activity of twenty cells was recorded during walking and compared in experiments with different distances between barriers. The mR in 50% and the dM in 75% of the neurones progressively increased when the distance between successive barriers was diminished. 5. The discharge rates of thirteen cells were compared in two different locomotor tasks: (i) when the cat stepped over barriers requiring hyperflexion of the limbs and (ii) when it walked on the flat with loads attached to the distal forelimbs causing a hyperactivity of flexor muscles. The activity of nine cells was different during stepping over the barriers compared to locomotion with loadings on the forelimbs. 6. The activity of 108 cells (twenty‐four PTNs) was recorded during walking along a horizontal ladder with flat rungs. The mR of 61% and the dM of 72% of cells changed by more than 20% during locomotion on the ladder compared with that on the flat (most often they increased). 7. The position of the peak rate relative to the step cycle did not differ in the majority of cells (in 78‐91% depending on the task) during locomotion on the flat, with the barriers or on the ladder.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses to sympathetic nerve stimulation of the sinus venosus of the toad.
Authors: Bramich N J , Brock J A , Edwards F R , Hirst G D
Published: December 2014

1. The changes in membrane potential produced by sympathetic nerve stimulation were recorded from sinus venosus preparations of the toad, Bufo marinus, in which beating had been prevented by the dihydropyridine calcium antagonist, nifedipine. 2. Supramaximal sympathetic stimuli initiated long‐lasting excitatory junction potentials which started with the same latencies, some 1 to 2 s, as did sympathetic tachycardias recorded from beating preparations. 3. Brief trains of stimuli increased the amplitude of excitatory junction potentials and shortened their latency of onset. Similarly when excitatory junction potentials were facilitated their latency of onset was shortened. 4. The time courses of excitatory junction potentials were prolonged by cooling the preparation but unchanged when the neuronal uptake of catecholamines was inhibited. 5. In arrested preparations, beta‐adrenoceptor activation causes a hyperpolarization, as did the inhibition of phosphodiesterases or the activation of adenylate cyclase. This contrasts with the depolarization produced by sympathetic nerve stimulation which could be mimicked by the rapid application of either adrenaline or noradrenaline but not by beta‐adrenoceptor activation, phosphodiesterase inhibition or by adenylate cyclase activation. 6. The results are discussed in relation to the idea that neuronally released adrenaline activates a set of adrenoceptors which are linked to a set of channels by a pathway that does not involve cyclic AMP.
Lactate and H+ effluxes from human skeletal muscles during intense, dynamic exercise.
Authors: Bangsbo J , Johansen L , Graham T , Saltin B
Published: December 2014

1. Lactate and H+ efflux from skeletal muscles were studied with the one‐legged knee extension model under conditions in which blood flow, arterial lactate and the muscle‐blood lactate concentration gradient were altered. Subjects exercised one leg twice to exhaustion (EX1, EX2), separated by a 10 min recovery and a period of intense intermittent exercise. After 1 h of recovery the exercise protocol was repeated with the other leg. Low‐intensity exercise was performed with one leg during the recovery periods, while the other leg was passive during its recovery periods. 2. Prior to, and immediately after, EX1 and EX2 and then 3 and 10 min after EX1, a biopsy was taken from the vastus lateralis of the exercised leg for lactate, pH, muscle water and fibre‐type determinations. Measurements of leg blood flow and venous‐arterial differences for lactate (whole blood and plasma), pH, partial pressure of CO2 (PCO2), haemoglobin, saturation and base excess (BE) were performed at the end of exercise and regularly during the recovery period after EX1. 3. The lactate release was linearly related (r = 0.96; P < 0.05) to the muscle lactate gradient over a range of muscle lactate from 0 to 45 mmol (kg wet wt)‐1. The muscle lactate transport was evaluated from the net femoral venous‐arterial differences (V‐Adiff) for lactate. This rose with increases in the muscle lactate gradients, but as the gradient reached higher levels the V‐Adiff lactate responded less than at smaller gradients. Thus, the lactate transport over the muscle membrane appears to be partly saturated at high muscle lactate concentrations. 4. The percentage of slow twitch (%ST) fibres was inversely related to the muscle lactate gradient, but it was not correlated to the lactate release at the end of the exercises. In spite of a significantly higher blood flow during active recovery, the lactate release was the same whether the leg was resting or performed low‐intensity exercise in the recovery periods. In several other conditions the muscle lactate and H+ gradients would have predicted that the V‐Adiff lactate would have been greater than it actually was. Thus, a variety of factors affect muscle lactate transport, including arterial lactate concentration, muscle perfusion, muscle contraction pattern and muscle morphology. 5. The muscle and femoral venous pH declined during EX1 to 6.73 and 7.14‐7.15, respectively, and they increased to resting levels during 10 min of either passive or active recovery.(ABSTRACT TRUNCATED AT 400 WORDS)
Heterogeneity of synaptic glutamate receptors on CA3 stratum radiatum interneurones of rat hippocampus.
Authors: McBain C J , Dingledine R
Published: December 2014

1. Whole‐cell recordings were made from interneurons located within CA3 stratum radiatum of neonate rat hippocampal slices. All experiments were performed in the continued presence of tetrodotoxin (1 microM) and bicuculline (5 microM) to permit the isolation of spontaneous miniature excitatory synaptic currents (mEPSCs). 2. Two distinct populations of interneurones were identified based on current‐voltage relations of kainate and the kinetic properties of spontaneous mEPSCs. These cell types were classified as type I and type II interneurones. 3. The I‐V relation of kainate in type I cells was linear or modestly outwardly rectifying. Currents reversed polarity close to 0 mV. The kainate I‐V relationship in type II interneurones was strongly inwardly rectifying with little or no outward current passed at potentials up to +50 mV. 4. Spontaneous mEPSCs were observed at a low frequency. At ‐70 mV mEPSCs received by type I interneurones had fast rise times (approximately 1 ms) and decay time constants (approximately 5 ms) and were mediated by alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid (AMPA) receptors. Miniature EPSCs on type I interneurones reversed polarity at approximately 0 mV. At +50 mV the kinetics of the mEPSCs on type I interneurones were slowed and comprised both AMPA and N‐methyl‐D‐aspartate (NMDA) receptor‐mediated components as revealed by their sensitivity to 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and D‐2‐amino‐5‐phosphonovaleric acid (D‐APV). 5. The kinetics of spontaneous mEPSCs on type II cells were slower than their type I counterparts at ‐70 mV. Spontaneous mEPSCs received by type II interneurones showed extreme inward rectification with no cells possessing fast events at +50 mV. In a few cells slowly rising and slowly falling spontaneous mEPSCs were observed at positive holding potentials. These events were abolished by D‐APV and were therefore mediated solely by NMDA receptor activation. 6. Type I or type II interneurones filled with Lucifer Yellow or biocytin possessed similar morphologies. Both cell types were typically large triangular cells with three to six branching dendrites often possessing varicosities. The dendrites of these interneurones arborized throughout strata radiatum, pyramidale, oriens and the molecular layer of the dentate gyrus. 7. In the majority of interneurones (both type I and II) the rise times of individual mEPSCs were correlated with their half‐width and decay time constant, suggesting that the shape of the mEPSC is in part determined by the dendritic origin of the synaptic input.(ABSTRACT TRUNCATED AT 400 WORDS)