bluuebunny/crossref_metadata_2025 huggingface dataset:
Permeation and block of N‐methyl‐D‐aspartic acid receptor channels by divalent cations in mouse cultured central neurones.
Authors: Mayer M L , Westbrook G L
Published: December 2014

1. Spinal cord and hippocampal neurones in cell culture were voltage clamped using the tight‐seal, whole‐cell recording technique. The concentration of sodium and a series of divalent cations in the extracellular media was varied to study permeation through excitatory amino acid receptor channels activated by the selective agonists N‐methyl‐D‐aspartic acid (NMDA), kainic acid and quisqualic acid. 2. On raising the extracellular calcium concentration, with [Na+]o held constant at 105 mM, the reversal potential of responses to NMDA shifted in the depolarizing direction. This shift was adequately described by the extended constant‐field equation over the range 0.3‐50 mM‐calcium. Using ionic activity coefficients we calculate a value of PCa/PNa = 10.6. Under the same experimental conditions the reversal potential of responses to kainic and quisqualic acids was much less affected by raising the calcium concentration, such that PCa/PNa = 0.15. A depolarizing shift of the NMDA reversal potential was also recorded during application of 20 mM‐barium, strontium or manganese, suggesting permeation of these ions. The permeability sequence was Ca2+ greater than Ba2+ greater than Sr2+ much greater than Mn2+. No depolarizing shift of the NMDA reversal potential occurred during application of 20 mM‐cobalt, magnesium or nickel. 3. In experiments in which the extracellular Na+ concentration was varied the extended constant‐field equation was adequate in predicting shifts of the NMDA reversal potential recorded on varying [Na+]o over the range 50‐150 mM, but failed to accurately predict the reversal potential of responses to NMDA with 10 mM‐[Ca2+]o and only 10 or 20 mM‐[Na+]o. These results imply an apparent increase in PCa/PNa on lowering [Na+]o and may result from interaction of permeant ions within the channel. 4. Barium and to a lesser extent calcium, but not strontium (all 20 mM), reduced the slope conductance of responses to NMDA recorded within +/‐ 15 mV of the reversal potential; over this limited range of membrane potential the current‐voltage relationship remained linear in the presence of each of these ions. In contrast manganese produced a strong, voltage‐dependent block of responses to NMDA, similar to that produced by magnesium, such that even close to the reversal potential the NMDA current‐voltage relationship was highly non‐linear. Thus manganese both permeates and blocks the NMDA receptor channel. 5. Raising the extracellular calcium concentration, from 0.1 to 5 mM, had two effects on the conductance mechanism activated by NMDA.(ABSTRACT TRUNCATED AT 400 WORDS)
Vagally mediated gastric motor and emetic reflexes evoked by stimulation of the antral mucosa in anaesthetized ferrets.
Authors: Andrews P L , Wood K L
Published: December 2014

1. In the urethane‐anaesthetized ferret chemical (NaCl, NaOH or HCl) or mechanical (stroking) stimulation of the gastric antral mucosa evoked a decrease in corpus pressure and inhibition of contractions in the presence of guanethidine, adrenalectomy and sectioned greater splanchnic nerves. 2. The fall in corpus pressure was present following administration of atropine but was abolished by vagotomy. 3. Preliminary evidence, using 100 mM‐NaOH as the stimulus, is presented that the effects on corpus motility are due to simultaneous activation of the vagal efferents supplying the intramural non‐adrenergic non‐cholinergic inhibitory neurones and inhibition of those supplying the intramural cholinergic neurones. 4. The possible roles of this antro‐corpus vago‐vagal reflex in the regulation of gastric emptying and in the prodromal phase of vomiting are discussed.
Activation heat in rabbit cardiac muscle.
Authors: Gibbs C L , Loiselle D S , Wendt I R
Published: December 2014

1. Activation heat was estimated myothermically in right ventricular papillary muscles of rabbits using several different methods. 2. Gradual pre‐shortening of muscles to a length (lmin) where no active force development took place upon stimulation led to relatively low estimates of activation heat (1.59 +/‐ 0.26‐2.06 +/‐ 0.57 mJ g‐1 blotted wet weight, mean +/‐ S.E.M., n = 10). 3. Quick releases applied during the latency period, before force development, from lmax to various muscle lengths allowed a heat‐stress relation to be established. The zero‐stress intercept of this relation estimated the activation heat to be 3.27 +/‐ 0.40 mJ g‐1; this was close to the experimentally measured value of 3.46 +/‐ 0.39 mJ g‐1 (mean +/‐ S.E.M., n = 23) found by quick release from lmax to lmin. 4. The magnitude of the activation heat measured by the quick‐release technique is dependent upon the extracellular Ca2+ concentration and there is good correlation between activation heat magnitude and peak developed stress. 5. In agreement with expectations based on the aequorin data of Allen & Kurihara (1982) a prolonged period of time spent at a short length is shown to depress the subsequently determined activation heat. 6. Hyperosmotic solutions (2.5 x normal) only abolished active stress development at low stimulus rates (0.2 Hz) and the activation heat measured at lmax under these conditions was 2.03 +/‐ 0.12 mJ g‐1 (mean +/‐ S.E.M., n = 6). This value was significantly lower than the latency release estimate of activation heat in the same preparations (2.93 +/‐ 0.39 mJ g‐1). 7. The latency release method of estimating activation heat results in activation heat values that account for approximately 30% of total active energy flux per contraction; a fraction comparable to that found in skeletal muscle. Calculations based on the data suggest that, under our experimental conditions, total Ca2+ release per beat lies between 50 and 100 nmol g‐1 wet weight which would produce less than half‐maximal myofibrillar ATPase activity when allowance is made for the passive Ca2+‐buffering capacity of the myocardial cell.
Activation of ion channels in the frog end‐plate by high concentrations of acetylcholine.
Authors: Colquhoun D , Ogden D C
Published: December 2014

1. The equilibrium relationship between acetylcholine (ACh) concentration and response (fraction of channels open), corrected for the effects of desensitization, has been estimated by single‐ion‐channel recording at the adult frog skeletal neuromuscular junction. At high ACh concentration channel openings occur in well‐defined clusters separated by long desensitized intervals. The response, po, was estimated as the proportion of time for which a single channel was open during a cluster. 2. At negative membrane potential (‐120 mV) po reached a maximum value of 0.9 at 100 microM‐ACh and was half‐maximum at 15 microM with a Hill slope of 1.6 at this point. At concentrations higher than 200 microM‐ACh, po declined as a result of open‐channel block by free ACh itself. 3. At positive membrane potentials (+100 mV) there was little channel block by ACh; po reached a maximum value of 0.41 at 500 microM‐ACh, with half‐maximum activation at 50 microM and Hill slope of 1.2 at this point. 4. Particular mechanisms for channel activation by ACh were fitted to the data by the method of least squares. Fits were fully determinate only if the two binding sites for ACh were assumed to be equivalent with no co‐operativity in the ACh binding reactions. At negative potential the microscopic equilibrium constant for binding was K1 = K2 = 77 microM and the equilibrium constant for channel opening (opening/closing rates, beta/alpha) was 32. At positive potential the affinity was slightly higher, K = 32 microM, which confirms the view that the binding sites for ACh are outside the membrane electric field. The equilibrium constant for channel opening was reduced to 0.7 mainly as a result of the much shorter open lifetime (increased closing rate alpha) at positive potentials. 5. The data were also fitted well by very high values of beta/alpha together with a high degree of negative co‐operativity or non‐equivalence in ACh binding affinity (K2 much greater than K1). A good fit could also be obtained with moderate positive co‐operativity combined with non‐equivalence of the binding sites. 6. A mechanism that postulates a receptor with two independent gating subunits provided a poor fit to the data at negative potential. 7. The rate constants for channel opening and ACh dissociation were estimated by constraining the fitted parameters so that the burst length for channel opening was equal to its observed value at low concentrations of ACh.(ABSTRACT TRUNCATED AT 400 WORDS)
Two long‐lasting central respiratory responses following acute hypoxia in glomectomized cats.
Authors: Gallman E A , Millhorn D E
Published: December 2014

1. Central respiratory response to acute (10 min) hypoxia, as measured by phrenic nerve activity, was determined in peripheral chemo‐denervated cats. 2. Hypoxia was induced by ventilating cats for 10 min at reduced inspired oxygen levels (inspired O2 fraction, FI,O2 = 0.06‐0.15). The degree of hypoxaemia was determined from an arterial blood sample and ranged from 'severe' (arterial O2 pressure, Pa,O2 less than 26 Torr) to 'mild' (Pa,O2 greater than 35 Torr). The respiratory response was monitored for 1 h following return to ventilation with 100% oxygen. 3. The results confirmed the finding of prolonged (greater than 60 min) inhibition of respiration upon return to hyperoxic conditions following severe hypoxia, as reported previously (Millhorn, Eldridge, Kiley & Waldrop, 1984). A new finding was a long‐lasting (greater than 60 min) facilitation of respiration following exposure to less severe (Pa,O2 greater than 35 Torr) hypoxia. 4. Medullary extracellular fluid pH was measured in six cats. Changes in pH could not explain either the prolonged inhibition following severe hypoxia or the long‐lasting facilitation observed following mild hypoxia. 5. Ablation studies were performed in order to determine the locations of the neuronal substrates for the inhibitory and facilitatory mechanisms. The results of this series of experiments indicate that the mesencephalon is necessary for activation of the inhibitory mechanism, while the facilitatory mechanism requires the presence of higher brain structures, notably the diencephalon. 6. Following removal of the diencephalon, the inhibitory response was seen following even mild hypoxic insults, i.e. those shown to produce facilitation in animals with intact brains. In the absence of the mesencephalon, neither prolonged inhibition nor prolonged facilitation could be produced following hypoxia. 7. It is proposed that there are two centrally mediated long‐lasting responses to acute hypoxia. Facilitation is seen following mild hypoxia. Inhibition is more likely following severe hypoxia. However, both mechanisms appear to be triggered simultaneously and the output of the central respiratory controller reflects the influence of each.
Effects of visual and non‐visual mechanisms on the vestibulo‐ocular reflex during pseudo‐random head movements in man.
Authors: Barnes G R , Eason R D
Published: December 2014

1. The behaviour of the vestibulo‐ocular reflex (VOR) in man was examined using pseudo‐random and sinusoidal whole‐body angular‐motion stimuli applied about the yaw axis by a servo‐controlled turn‐table. 2. The VOR response was assessed in four conditions; during fixation on a head‐fixed target (HFT); during attempted fixation in the dark of an imagined head‐fixed (IHFT) or earth‐fixed target (IEFT) and in darkness (DRK) whilst performing an auditory discrimination task. 3. When the pseudo‐random stimulus was composed of four sinusoids, the three lowest frequencies (0.11, 0.24 and 0.37 Hz) were maintained constant whilst the highest frequency (F4) was varied from 0.39 to 2.08 Hz. In darkness (DRK condition) and when imagining a head‐fixed target (IHFT condition) the gain of slow‐phase eye velocity was not significantly affected by the frequency of the highest‐frequency component, although there were significant changes in the phase for the IHFT condition. 4. During fixation of a real head‐fixed target (HFT condition), both the gain and phase of eye velocity were significantly modified by the frequency (F4) of the highest‐frequency component. When F4 was 0.39 Hz, all frequency components had a low gain (mean 0.05), but as F4 was increased there was a significant (P less than 0.001) increase in gain for all three low‐frequency components which reached a maximum (mean 0.17) when F4 was 2.08 Hz. However, the gain for the highest frequency component always remained comparable to that obtained in response to a single discrete sinusoid of the same frequency. 5. When the stimulus was composed of only two sinusoids a similar increase in gain of the lower‐frequency (0.22 Hz) component was observed in the head‐fixed target condition as the frequency of the higher‐frequency component was increased from 0.39 to 2.78 Hz. However, VOR gain was not significantly modified by the frequency of the higher‐frequency component when subjects imagined a head‐fixed or earth‐fixed target in darkness. 6. The findings indicate that high levels of VOR suppression can be achieved in the head‐fixed target condition with pseudo‐random stimuli when all frequency components are below 0.4 Hz. But if the highest‐frequency component rises above 0.8 Hz, optimum suppression is confined to the highest‐frequency component, whilst suppression of the low‐frequency components is significantly reduced.(ABSTRACT TRUNCATED AT 400 WORDS)
Barium‐induced automatic activity in isolated ventricular myocytes from guinea‐pig hearts.
Authors: Hirano Y , Hiraoka M
Published: December 2014

1. A suction‐pipette whole‐cell clamp technique was applied to single ventricular myocytes isolated from guinea‐pig hearts, in order to investigate the ionic mechanism underlying Ba2+‐induced automatic activity. 2. The application of 0.1 mM or less Ba2+ to the myocytes caused a depolarization of the resting membrane potential without inducing spontaneous activity. The stimulated action potential showed a prolonged repolarization phase followed by an after‐hyperpolarization. 3. Concentrations of Ba2+ of 0.2 mM or greater produced further depolarization of the resting membrane potential and induced spontaneous activity. Spontaneous activity developed from the slow diastolic depolarization preceded by after‐hyperpolarizations of spontaneous or stimulated action potentials. 4. Under voltage‐clamp conditions, a decaying outward or inward current in response to hyperpolarizing clamp steps from depolarized potentials appeared in the presence of Ba2+. The Ba2+‐induced current decay showed a faster time course with increasing hyperpolarizing clamp pulses and reversed its polarity at around ‐90 mV, the presumed equilibrium potential for K+ (EK). In the late current‐voltage (I‐V) relation, Ba2+ almost eliminated the inward‐rectifying property. These effects on the cardiac membrane are consistent with a time‐ and voltage‐dependent blocking action of Ba2+ on inward‐rectifying K+ currents as reported for other excitable tissues. 5. The concentration‐ and voltage‐dependence of the steady‐state block of the inward rectifying K+ current (IK1) was fitted by a simple model assuming 1:1 binding of Ba2+ to a site within the membrane. The apparent dissociation constant at the holding potential of 0 mV (K(0] was 0.3 mM, and the parameter for the membrane potential dependence of Ba2+ blockade (mu) was approximately 0.5. 6. A computer model of the ventricular action potential proposed by Beeler & Reuter (1977) was modified, based on the recent experiments using single cardiac myocytes. The modifications include (1) the current‐voltage relationship of IK1, (2) time courses of activation and inactivation of the Ca2+ current (ICa), (3) the activation voltage range for the delayed outward K+ current (IK). 7. The time‐ and voltage‐dependent blocking action of Ba2+ on IK1, including the experimentally determined values for K(0) and mu, were incorporated into the modified version of the action potential model. The computer model reproduced an after‐hyperpolarization at doses of Ba2+ lower than 0.1 mM and automatic activity at doses higher than 0.15 mM.(ABSTRACT TRUNCATED AT 400 WORDS)
Cerebro‐cerebellar projections from the lateral suprasylvian visual area in the cat.
Authors: Kato N , Kawaguchi S , Miyata H
Published: December 2014

1. A projection from the medial bank of the lateral suprasylvian visual area, one of the targets of the cerebello‐cerebral projection, back to the cerebellar cortex was demonstrated electrophysiologically in the cat. The anatomical pathways underlying this projection were investigated using orthograde and retrograde transport of wheatgerm‐agglutinin‐conjugated horseradish peroxidase (WGA‐HRP). 2. Responses were recorded in the cerebellar cortex on stimulation of the medial bank of the lateral suprasylvian area, and were compared with those evoked by stimulation of the motor cortex and the crown part of the parietal association cortex. 3. Responses induced by stimulation of the lateral suprasylvian area were shown to consist of early mossy and late climbing fibre responses. The mossy fibre response was evoked, at a latency of 2‐3 ms, predominantly in the lateral part of the contralateral cerebellar cortex (mainly, crus I, crus II, dorsal paraflocculus and paramedian lobule) and the posterior part of the vermis (mainly, lobules VII and VIII). Climbing fibre responses were elicited with the preceding mossy fibre responses and were elicited at a much longer latency than the motor cortex‐induced climbing fibre response. 4. The orthograde and retrograde HRP studies suggested that the mossy fibre response is mediated by the pontine grey whereas the climbing fibre response is conveyed indirectly to the inferior olive which sends the climbing fibres to the cerebellar cortex. After WGA‐HRP injections into both the medial bank of the lateral suprasylvian area and the cerebellar responsive area, orthogradely labelled terminals of cortico‐pontine projection fibres and retrogradely labelled ponto‐cerebellar neurones were found in the pontine grey, where distributions of the two kinds of labelling overlapped. On the other hand, retrograde neuronal labelling alone was found in the inferior olive, implying that the climbing fibre responses evoked from the lateral suprasylvian area were relayed via indirect cortico‐olivary pathways.
Potassium currents in rat type II alveolar epithelial cells.
Authors: DeCoursey T E , Jacobs E R , Silver M R
Published: December 2014

1. Type II alveolar epithelial cells isolated from adult rats and grown in primary culture were studied using the whole‐cell configuration of the gigohm‐seal voltage clamp technique. 2. The average specific capacitance of type II cells was 2.5 microF/cm2, suggesting that type II cell membranes in vitro are irregular, with an actual area more than twice the apparent area. 3. Most type II cells have time‐ and voltage‐dependent outward currents carried by potassium ions. Potassium currents activate with a sigmoid time course upon membrane depolarization, and inactivate during maintained depolarization. The average maximum whole‐cell K+ conductance was 1.6 nS. 4. Two distinct types of K+‐selective channels underlie outward currents in type II cells. Most cells have currents resembling delayed rectifier K+ currents in skeletal muscle, nerve and immune cells. A few cells had a different type of K+ conductance which is more sensitive to block by tetraethylammonium ions, has faster 'tail currents', and activates at more positive potentials. 5. In some experiments, individual type II cells were identified by staining with phosphine, a fluorescent dye which is concentrated in lamellar bodies. Both types of K+ channels were seen in type II cells identified with this dye. 6. Phosphine added to the bathing solution reversibly reduced K+ currents and shifted K+ channel activation to more positive potentials. Excitation of phosphine to fluoresce reduced irreversibly K+ currents in type II cells. The usefulness of phosphine as a means of identifying cells for study is discussed.
Age and the transmittance of the human crystalline lens.
Authors: Weale R A
Published: December 2014

1. Conflicting data both on the transmission of the human crystalline lens in the ultra‐violet part of the spectrum and on its variation with age necessitate a re‐examination of the subject. 2. Twenty‐four excised lenses in the age range of 0‐85 years were studied with a Perkin‐Elmer spectrophotometer between 327 and 700 nm. 3. Some lenses were homogenized and the homogenates were similarly examined. 4. A systematic increase in absorbance with age was observed both in the visible and the ultra‐violet parts of the spectrum. 5. An exponential function describes the data, facilitating comparison with, and prediction of, other values. 6. The absorbance of homogenized material was found to be predictable from that of intact lenses, and does not support the notion that mechanical trauma may account for high values in earlier studies.
Coupling of active sodium transport to oxidative metabolism in the rabbit distal colon.
Authors: Durand J , Durand‐Arczynska W , Wankmiller D
Published: December 2014

1. Active transepithelial Na+ transport (Ji) and O2 consumption (Jr) were measured simultaneously in rabbit distal colon, under standard (control) incubation conditions and after various manoeuvres, known to inhibit Na+ transport. 2. The determination of Jr was complicated by the presence of fluctuations of the PO2 in the incubation solution and by spontaneous variations of the tissue respiration, which usually declined slowly with time. 3. The control values of Ji and Jr after 2 h incubation were 55 +/‐ 4 nequiv min‐1 cm‐2 and 16 +/‐ 1 nmol O2 min‐1 cm‐2, respectively (n = 44). The electrical resistance was 386 +/‐ 23 omega cm2; it was stable over 6 h. 4. Ji was reduced to a very low level with either amiloride, ouabain or Na+ substitution with choline. In all instances, Jr decreased concomitantly by 15‐30%. 5. A plot of the change in Jr versus the change in Ji gave a straight line for all situations, i.e. for the spontaneous decline of Na+ transport and respiration and for the effects of the inhibitors. 6. The linearity between Jr and Ji allows for the determination of a stoichiometric ratio. It is of similar magnitude, when calculated either with the data of spontaneous variations or with those obtained by the action of any inhibitor tested. It is 15‐20 Na+ ions per O2 molecule, a value close to that reported previously for amphibian epithelia and also close to the maximum theoretical value of 18 Na+ ions per O2 molecule.
The effects of metabolic acidosis on renal function of fetal sheep.
Authors: Kesby G J , Lumbers E R
Published: December 2014

1. The effects of I.V. infusions of 6.7‐19.3 mmol hydrochloric acid/kg on fetal renal function were studied in fourteen chronically catheterized fetal sheep aged 121‐143 days. Infusion of acid caused arterial pH and plasma bicarbonate levels to fall (P less than 0.0005, P less than 0.001). These remained low for the next 3 h. Plasma chloride levels increased (P less than 0.0005). There were no other changes in plasma electrolytes nor in plasma osmolality. 2. Fetal glomerular filtration rate did not change; the fractional reabsorptions of sodium, chloride and phosphate all decreased (P less than 0.005). Initially urine volume did not change but urinary osmolality increased (P less than 0.0005). Fetal urinary pH fell abruptly, titratable acid excretion increased, urinary ammonium excretion increased (P less than 0.0005) but urinary bicarbonate excretion remained unchanged. Thus, net acid excretion increased significantly (P less than 0.0005). 3. Twenty‐six hours after infusion of acid, fetal arterial pH, bicarbonate levels, urinary pH, titratable acid and ammonium excretion were no different from control. Net acid excretion was still increased (P less than 0.05), urine flow rate was less (P less than 0.01) and urinary osmolality still increased (P less than 0.05). 4. There were no differences in arterial blood gases nor in pH of four fetuses which died during or shortly after infusion of acid. However, prior to acid infusion they were already excreting significantly greater amounts of phosphate (P less than 0.01), ammonium and titratable acid (P less than 0.02). Thus the fetal kidney responds to a metabolic acidosis by excreting more acid and by generating more bicarbonate, but this response is limited.
Slow excitatory postsynaptic currents mediated by N‐methyl‐D‐aspartate receptors on cultured mouse central neurones.
Authors: Forsythe I D , Westbrook G L
Published: December 2014

1. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked between pairs of cultured neurones from either hippocampus or spinal cord were examined using the tight‐seal whole‐cell recording technique. 2. Using the selective N‐methyl‐D‐aspartate (NMDA)‐receptor antagonist, 2‐amino‐5‐phosphonovaleric acid (APV), two components of the EPSP could be resolved in cultures from both brain regions. The APV‐sensitive (slow) component had the same latency, but a much slower time‐to‐peak and longer duration than the APV‐resistant (fast) component. Other NMDA antagonists such as ketamine also selectively blocked the slow component of the EPSP. 3. In Mg2+‐free medium, the dual‐component EPSP had a duration lasting up to 500 ms, greatly exceeding the membrane time constant of the postsynaptic neurone, suggesting that persistent activation of NMDA receptors was responsible for the long duration of the APV‐sensitive component. 4. Under voltage clamp the excitatory postsynaptic currents (EPSCs) also showed fast and slow components, both of which had a reversal potential near 0 mV in physiological saline. The synaptic current could be fitted with a sum of two exponentials with a decay time constant for the slow EPSC near 80 ms. The slow current contributed approximately 50% of the total charge transfer during the EPSC. 5. In Mg2+‐containing medium, the peak of the fast component was voltage insensitive, whereas the synaptic current measured at a latency of 10‐50 ms was voltage dependent with a region of negative slope conductance at membrane potentials hyperpolarized to ‐30 mV. 6. Raising [Ca2+]o from 1 to 20 mM resulted in a shift of the reversal potential of the APV‐sensitive component from near 0 mV to + 10 mV, but the reversal potential of the fast component remained near 0 mV. This suggests that conductances with different ionic permeability underlie the two components of the EPSC and that the slow component is highly permeable to Ca2+ as well as to monovalent cations. 7. Our results demonstrate that two functionally distinct excitatory amino acid receptor channels are simultaneously activated by transmitter release from a single presynaptic neurone. The conductance mechanism underlying the slow component of the EPSP displays the voltage dependence and Ca2+ permeability expected for NMDA‐receptor channels. We suggest that the available conductance generating the slow EPSP may be sufficient, even at low firing rates, to influence excitability on both a short‐term and more long‐lasting basis.
Effect of theophylline on the apical sodium and chloride permeabilities of amphibian skin.
Authors: Katz U , Van Driessche W
Published: December 2014

1. The effects of theophylline (1 mmol/l) on the sodium transport (short‐circuit current, Isc) and transepithelial conductance (Gtotal) through toad (Bufo viridis) and frog (Rana temporaria and Rana esculenta) skin were investigated. 2. In toad skin incubated with nitrate Ringer solution on the apical side, theophylline induced an increase in Isc similar to that in frog skin bathed with chloride Ringer solution. 3. The increase in Isc could be attributed to recruitment of sodium channels, without affecting the single‐channel current. 4. Chloride‐bathed toad skin responded to theophylline with a large increase in transepithelial conductance, in addition to the increased Isc. 5. Chloride replacement by nitrate eliminated the effect of theophylline on the conductance increase, but the Isc response was even larger. 6. The results are discussed in relation to the localization of the cellular chloride pathway to the mitochondria‐rich cells.
Origin of the specific H reflex facilitation preceding a voluntary movement in man.
Authors: Riedo R , Rüegg D G
Published: December 2014

1. In a reaction time situation, the monosynaptic spinal reflex (H reflex) is facilitated before the onset of an electromyographic (EMG) response. The aim of the present investigation was to test if the facilitation can be attributed either to a subliminal depolarization of motoneurones or to an increase of the excitatory effect of the afferent volley reaching the motoneurones. 2. At the onset of an acoustic warning signal, human subjects were required to concentrate on a reaction time task and, in addition, to initiate a steady isometric plantar flexion of medium intensity in both feet. In response to a following visual stimulus, they carried out a ballistic plantar flexion randomly with the right or left foot. At different times after the visual reaction signal, H reflexes were elicited bilaterally. 3. The facilitation of the H reflex was similar in the presence and absence of a steady activation. In addition, the facilitations were similar in absolute amplitude and duration when the stimuli evoking the H reflexes were at threshold intensities, or at an intensity which produced control H reflexes of 60% maximum amplitude. 4. In a second series of experiments, no H reflexes were elicited but the strength of the steady plantar flexion was varied. Premotor time, i.e. the interval between the onset of the visual stimulus and the EMG response, and reaction time, i.e. the interval between the onset of the visual stimulus and the mechanical response, were computed. Neither parameter depended significantly on the intensity of steady flexion and they were the same with steady flexion as without. 5. The rectified EMG records and the torque records were aligned by the end of premotor time. Three‐dimensional displays of average activity as a function of time and steady activation level were computed. No activation before premotor and reaction time was detected which could have been related to the H reflex facilitation. 6. The present results suggest that all motoneurones, in particular those being activated during the voluntary contraction, can contribute to the H reflex facilitation before movement onset and that the basis of this facilitation is an enhanced excitatory effect of the afferent volley elicited by the H reflex stimulus. Mechanisms leading to the facilitation could be removal of presynaptic inhibition at I a terminals or facilitation of interneurones intercalated in polysynaptic components of the reflex pathways.
Effect of Ca2+ channel blockers on K+ contractures in twitch fibres of the frog (Rana pipiens).
Authors: Gamboa-Aldeco R , Huerta M , Stefani E
Published: December 2014

1. The effects of Ca2+ channel blockers (nifedipine, nitrendipine and diltiazem) were tested on K+ contractures in single muscle fibres of the frog, Rana pipiens. 2. Nifedipine (1 microM) reduced the area under K+ contractures to 24 +/‐ 9% (4) (100 mM‐K+) and 34 +/‐ 24% (4) (190 mM‐K+). Nitrendipine (0.1 microM) reduced the area to 30 +/‐ 10% (4) (120 mM‐K+). The blockade of the contractures was reversible. 3. Diltiazem (1 microM) shortened the first 190 mM‐K+ contracture without affecting the peak amplitude. The first contractures, performed at 15‐20 min after the removal of diltiazem, were greatly reduced to 29 +/‐ 14% (4). This effect was reversed after three to five contractures in the absence of the drug. Similar results were obtained with 60 and 100 mM‐K+. 4. The resting potential in control saline and after a brief exposure to 120 mM‐K+ was not affected by the dihydropyridines and diltiazem. 5. Slow and fast Ca2+ currents were not modified by 1 microM‐diltiazem at any stimulation rate or with pre‐pulse depolarizations. Diltiazem (50 microM) did not affect the fast Ca2+ current and reduced the slow one to 48 +/‐ 10% (4). 7. The reduction of K+ contractures by Ca2+ channel blocking agents was not related to a blockade of Ca2+ currents. This can be tentatively explained by interactions of these compounds on membranes sites which regulate the coupling between membrane depolarization and contraction.
Inhibition of chloride self‐exchange with stilbene disulphonates in depolarized skeletal muscle of Rana temporaria.
Authors: Skydsgaard J M
Published: December 2014

1. The inhibition of 36Cl efflux with stilbene disulphonates, SD, has been studied under conditions of chloride equilibrium in depolarized fibre bundles from frog semitendinosi. The chosen probes were the aminoreactive derivative SITS and the derivative DNDS with no aminoreactive group. SD were added to the medium during 36Cl efflux allowing the estimation of fractional inhibition after a single 36Cl loading. 2. Both probes inhibited chloride self‐exchange reversibly within the pH range 5.5‐9.5 under study. 3. At SD concentrations above the half‐inhibition concentration the inhibition reached a steady level with a time lag equal to that required for extracellular fluid change. The time constant for reversibility upon the removal of SD increased with decreasing pH, but rapid reversibility always appeared upon an increase of pH to 7.2. These findings suggest that SD may enter the membrane at low pH, but that the inhibitory action is confined to superficial membrane sites. 4. The inhibitory power of both probes showed a pronounced pH dependence, pK approximately 7. The half‐inhibition concentration increased about 6‐7 times when pH was lowered one unit from the pK value. 5. The apparent affinity of SITS to the transport system was about 5 times higher than that of DNDS. The apparent dissociation constants at neutral pH were 8.5 x 10(‐5) M (SITS) and 4.5 x 10(‐4) M (DNDS). Both probes showed a maximal inhibition close to 100% at neutral pH and approximately 85% at pH 5.5. 6. The inhibition depended on the chloride concentration in a way consistent with competitive inhibition in both neutral and acid media. 7. The results are consistent with the classical model of anion transport in frog muscle, suggesting that SD and chloride may compete for binding to a site with increasing anion affinity upon protonation; the results do not, however, exclude that the conductive and the non‐conductive chloride transport modes in frog muscle are mediated by separate SD‐sensitive transport pathways.
Excretion of para‐aminohippurate in the isolated perfused rat kidney: net secretion and net reabsorption.
Authors: MacDougall M L , Wiegmann T B
Published: December 2014

1. The excretion of para‐aminohippurate (PAH) in the isolated perfused rat kidney was examined over a wide range of perfusate PAH concentrations (15 microM to 6 mM). PAH excretion increased steadily over the range of perfusate concentrations, reaching a maximal excretion rate of 3.28 mumol/min at a free‐PAH concentration of 6 mM. 2. Tubular transport of PAH was evaluated from the difference between ultrafiltered PAH and excreted PAH. Net PAH secretion was observed at low perfusate free PAH concentrations. Net PAH transport was zero at a perfusate free PAH concentration of 2.1 mM. Above this level there was progressive net reabsorption. 3. Probenecid (2.5 mM) decreased PAH secretion to 18% of the initial value at 129 microM‐free PAH (P less than 0.05). Probenecid had no effect on net reabsorption of PAH at high perfusate levels of the anion. 4. Alanine (5 mM) decreased net PAH secretion by 50% at low free PAH concentrations (P less than 0.05) and decreased net PAH reabsorption by 50% at at a free PAH concentration of 6 mM (P less than 0.05). These effects could not be related to effects of PAH, probenecid or alanine on glomerular filtration rate (GFR), vascular resistance or electrolyte excretion. 5. The results confirm the existence and integrity of the proximal tubular organic anion secretory system in the isolated kidney. In addition, net PAH reabsorption occurs at high perfusate levels.
Human muscle fatigue: frequency dependence of excitation and force generation.
Authors: Cooper R G , Edwards R H , Gibson H , Stokes M J
Published: December 2014

1. Human adductor pollicis was fatigued using intermittent trains of programmed stimulation at 1, 10, 20, 50, 100 and 1 Hz, during activity with and without circulatory occlusion, to investigate the relationships between force generation, excitation and maximal relaxation rate (MRR). 2. The relationship between force generation and excitation was markedly dependent on stimulation frequency. Force loss was greatest at low frequencies, with little reduction in excitation, but as frequency increased force was well maintained despite marked loss of excitation. 3. Changes in MRR during activity and recovery were independent of stimulation frequency. 4. Marked increases of force at 1 Hz (pre‐tetanic) and 10 Hz occurred, with little reduction in excitation, during activity with and without circulatory occlusion. This may be due to post‐tetanic potentiation in addition to slowing of relaxation (MRR). 5. At high frequency a 'safety factor' may thus operate to maintain force, despite obvious loss of excitation, while at low frequencies there may be marked potentiation of force, despite unchanged excitation. These mechanisms could permit resistance to fatigue with muscle function remaining optimal over a range of conditions.
Filtration coefficient and osmotic reflection coefficient to albumin in rabbit submandibular gland capillaries.
Authors: Gamble J , Smaje L H , Spencer P D
Published: December 2014

1. The isolated perfused submandibular salivary gland of the rabbit has been used in order to make estimates of the filtration coefficient (Kf) and reflection coefficient (sigma d) of the capillary wall to albumin. 2. An isogravimetric preparation was used and in paired experiments the value for Kf obtained in glands perfused with albumin‐Krebs solution, 0.96 +/‐ 0.086 (mean +/‐ S.E. of mean) ml min‐1 mmHg‐1 100 g‐1, was not significantly different from that in blood‐perfused glands, 0.90 +/‐ 0.15. 3. On analysing the data for reflection coefficient, it was concluded that the above values underestimated Kf by about 30%; using corrected values for Kf, osmotic reflection coefficients were determined from the weight changes following a sudden change in the oncotic pressure of the perfusate. The value for sigma d to albumin lay between 0.79 and 1.0, the lower value being obtained after the Kf correction. 4. The high hydraulic conductivity, combined with sieving properties comparable to those in continuous capillaries, is consistent with other data on fenestrated capillaries. 5. Finally, it was observed that, while the Kf value calculated from the initial flux rate was similar whether measured during fluid efflux from or influx into the microvasculature, on returning to the initial conditions after raising osmotic pressure, efflux was now more rapid than influx. This phenomenon is discussed in relation to readjustment of Starling forces and the possible existence of an asymmetric double membrane in the capillary, interstitium system and cells of the salivary gland.
Mechanism of contracture on cooling of caffeine‐treated frog skeletal muscle fibres.
Authors: Horiuti K
Published: December 2014

1. In order to clarify the mechanism of contracture on cooling of caffeine‐treated intact muscle fibres, the temperature dependence of a calcium (Ca2+) release mechanism, 'Ca2+‐induced Ca2+ release', of the sarcoplasmic reticulum (SR) was examined in skinned frog muscle fibres. 2. Skinned fibres in a solution containing 1.2 mM‐caffeine and 0.7 mM‐EGTA (Mg2+, 1.5 mM, Mg‐ATP, 3.5 mM, pH 7), contracted on cooling (from 22 to 2 degrees C) due to Ca2+ release from the SR. 3. The rate of Ca2+ release from skinned fibre SR in a medium which contained Ca2+ ions (with 10 mM‐EGTA) and no ATP salts, was determined under various conditions using the 'caffeine method.' 4. In the absence of Mg2+ ions, adenine nucleotides and caffeine, the rates at room temperature (21‐22 degrees C) were 3‐4 times greater than those at a lower temperature (1.5‐3 degrees C), at any concentrations of Ca2+ ions external to the SR. 5. In the presence of Mg2+ ions (1.5 mM) and beta,gamma‐methylene ATP (1 mM), the effect of temperature on the rates disappeared in Ca2+‐containing media, although the effect remained in Ca2+‐free medium. 6. When caffeine (1.2 mM), which is a potentiator of the Ca2+‐induced Ca2+ release, was added to the test medium with Mg2+ and beta,gamma‐methylene ATP, the resulting potentiating effect was several times greater than that at lower temperature. 7. In order to examine the temperature dependence of the Ca2+ pump activity of the SR, the initial rate of Ca2+ uptake by the empty SR was determined under various conditions in the presence of Mg2+ ions (1.5 mM) and Mg‐ATP (3.5 mM). The Q10 of the pump activity was around 2.0 at the Ca2+ ion concentrations examined (less than 10(‐6) M). 8. A numerical model based on the results obtained, together with some reasonable assumptions, suggested that both suppression of the Ca2+ pump and enhancement of the Ca2+ release contribute to the cooling contracture of caffeinized fibres.
Thin filament regulation of shortening velocity in rat skinned skeletal muscle: effects of osmotic compression.
Authors: Metzger J M , Moss R L
Published: December 2014

1. Maximum shortening velocity (Vmax) was examined in skinned single fibres from rat slow‐twitch soleus muscles at various degrees of Ca2+ activation of the thin filament, in the presence and absence of osmotic compression induced by 5% dextran. 2. At maximal levels of Ca2+ activation, Vmax remained constant as the extent of shortening was varied, with values averaging 1.43 +/‐ 0.05 muscle lengths/s (mean + S.E.M., n = 13). When thin filament activation was reduced by lowering the concentration of Ca2+, unloaded shortening consisted of an initial high‐velocity phase for extents of shortening in the range 20‐80 nm/half‐sarcomere, and a subsequent low‐velocity phase for greater extents of shortening. 3. In the absence of dextran, Vmax in the high‐velocity phase of shortening was relatively invariant over a wide range of activation; however, at very low levels of activation, yielding tensions less than 5% of the peak value. Vmax declined precipitously. In contrast, fibres compressed radially with dextran to diameters comparable to those of intact fibres demonstrated a marked decrease in Vmax in the high‐velocity phase when thin filament activation was varied over a wide range. These findings are consistent with the idea that cross‐bridges in the expanded filament lattice of skinned fibres do not bear as great an axial compressive force as in intact fibres (Goldman & Simmons, 1986; Goldman, 1987) but instead buckle as the fibre shortens. 4. The value of Vmax in the low‐velocity phase of shortening decreased as thin filament activation was reduced in both control and osmotically compressed fibres. The low‐velocity phase, which occurred only at reduced levels of thin filament activation, may be a manifestation of a population of slowly dissociating crossbridges which with shortening become negatively strained and oppose contraction.
Synaptic rearrangements and alterations in motor unit properties in neonatal rat extensor digitorum longus muscle.
Authors: Balice-Gordon R J , Thompson W J
Published: December 2014

1. We have used in vitro intracellular recordings and measurements of the contractile properties of single motor units to examine the changes in muscle innervation occurring during the post‐natal development of a fast‐twitch muscle in the hindlimb of the rat, the extensor digitorum longus (EDL). 2. Intracellular recordings of end‐plate potentials evoked in response to graded stimulation of the nerve supply to the muscle indicate that during the first day after birth, each muscle fibre receives synaptic input from at least two motoneurones and that some muscle fibres receive as many as six such inputs. With subsequent development, most of this polyneuronal innervation is eliminated: the first singly innervated fibres are encountered on day 3; by day 18 fewer than 5% of the fibres remain polyneuronally innervated. These results show that there are quantitative differences in post‐natal synapse elimination in EDL compared to its well‐studied counterpart, the soleus. Although the great majority of fibres in both muscles become singly innervated at about 18 days, the first singly innervated fibres appear at least a week earlier in the EDL. None the less, synapses are lost from EDL at about half the rate they are lost from soleus. 3. The number of motor units, determined by counting the number of twitch increments produced by graded stimulation of ventral root filaments teased to contain only a few EDL motor axons, remains unchanged from an average of forty‐one from post‐natal day 1 to day 17. In addition, the number of muscle fibres counted in muscle cross‐sections stained with an anti‐myosin antibody increases less than 10% from birth to adulthood. Therefore, synapse elimination in EDL occurs with a largely constant population of muscle fibres as well as motoneurones. 4. Measurements of tensions generated by single motor units indicate that the average size of a motor unit declines from 6.8% of the muscle fibres at day 1 to 2.3% at 17 days. This result indicates that each motoneurone, on average, comes to innervate threefold fewer muscle fibres. Motor units derived from each of the spinal segments innervating the muscle undergo equivalent reductions in motor unit size, indicating that there is no segmental disproportion to synapse elimination in this muscle. At all ages, there is a large diversity of motor unit sizes in the muscle. Synapse elimination therefore appears to maintain rather than decrease this diversity.(ABSTRACT TRUNCATED AT 400 WORDS)
Sensory input to cells of origin of uncrossed spinocerebellar tract located below Clarke's column in the cat.
Authors: Aoyama M , Hongo T , Kudo N
Published: December 2014

1. Sensory inputs to and locations of uncrossed spinocerebellar tract neurones in the lower lumbar cord were studied in chloralose‐anaesthetized cats. 2. Neurones with axons ascending in the ipsilateral thoracic funiculi and projecting to the cerebellum were found mainly dorsal to the central canal (laminae V and VI) in the L5‐L6 segments, i.e. at levels caudal to Clarke's column. Axons considered to originate from these cells were located in the dorsal half of the lateral funiculus at the level of L2, intermingled with axons of the dorsal spinocerebellar tract originating at the levels of Clarke's column. 3. Synaptic actions of primary afferents on neurones with antidromic invasion following stimuli applied to ipsilateral thoracic funiculi or to the cerebellum were investigated using intracellular or extracellular recording in the caudal lumbar segments. 4. Monosynaptic excitatory effects were evoked by electrical stimulation of group I muscle afferents of the hindlimb ipsilateral to the cell body. The majority of neurones received monosynaptic excitation from two or more muscles, predominantly extensors. They were frequently co‐excited by group Ia muscle spindle and group Ib tendon organ afferents. 5. Volleys in cutaneous afferents produced excitation with short central latencies. In addition to the monosynaptic and disynaptic excitation from low‐threshold cutaneous afferents, there were indications of monosynaptic effects from slightly slower conducting fibres. The majority of these neurones also received monosynaptic excitation from group I muscle afferents. Neurones with cutaneous input tended to be located more dorsally compared with those responding only to muscle afferents. 6. Volleys in joint afferents produced monosynaptic excitatory postsynaptic potentials (EPSPs) in the neurones with EPSPs from group I or group I and cutaneous afferents. 7. Some neurones were disynaptically inhibited from group I muscle afferents. Convergence of monosynaptic group I excitation and disynaptic group I inhibition occurred in varieties of patterns. 8. Polysynaptic excitation, inhibition or mixed effects of both were evoked from ipsilateral cutaneous afferents and high‐threshold muscle and joint afferents, whereas effects from the controlateral afferents were feeble.(ABSTRACT TRUNCATED AT 400 WORDS)