bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of sympathetic nervous system activation on the tonic vibration reflex in rabbit jaw closing muscles.
Authors: Grassi C , Deriu F , Passatore M
Published: December 2014

1. In precollicular decerebrate rabbits we investigated the effect of sympathetic stimulation, at frequencies within the physiological range, on the tonic vibration reflex (TVR) elicited in jaw closing muscles by small amplitude vibrations applied to the mandible (15‐50 microns, 150‐180 Hz). The EMG activity was recorded bilaterally from masseter muscle and the force developed by the reflex was measured through an isometric transducer connected with the mandibular symphysis. 2. Unilateral stimulation of the peripheral stump of the cervical sympathetic by the TVR, and a marked decrease or disappearance of the ipsilateral EMG activity. No significant changes were detected in the EMG contralateral to the stimulated nerve. Bilateral CSN stimulation reduced by 60‐90% the force reflexly produced by the jaw closing muscles and strongly decreased or suppressed EMG activity on both sides. This effect was often preceded by a transient TVR enhancement, very variable in amplitude and duration, which was concomitant with the modest increase in pulmonary ventilation induced by the sympathetic stimulation. 3. During bilateral CSN stimulation, an increase in the vibration amplitude by a factor of 1.5‐2.5 was sufficient to restore the TVR reduced by sympathetic stimulation. 4. The depressant action exerted by sympathetic activation on the TVR is mediated by alpha‐adrenergic receptors, since it was almost completely abolished by the I.V. administration of either phentolamine or prazosin, this last drug being a selective antagonist of alpha 1‐adrenoceptors. The sympathetically induced decrease in the TVR was not mimicked by manoeuvres producing a large and sudden reduction or abolition of the blood flow to jaw muscles, such as unilateral or bilateral occlusion of the common carotid artery. 5. The effect of sympathetic stimulation was not significantly modified after denervation of the inferior dental arch and/or anaesthesia of the temporomandibular joint, i.e. after having reduced the afferent input from those receptors, potentially affected by CSN stimulation, which can elicit either a jaw opening reflex or a decrease in the activity of the jaw elevator muscle motoneurons. 6. These data suggest that, when the sympathetic nervous system is activated under physiological conditions, there is a marked depression of the stretch reflex which is independent of vasomotor changes and is probably due to a decrease in sensitivity of muscle spindle afferents.
Two phosphatase sites on the Ca2+ channel affecting different kinetic functions.
Authors: Ono K , Fozzard H A
Published: December 2014

1. Changes in dihydropyridine‐sensitive (L‐type) Ca2+ channel kinetics were studied after prolongation of intrinsic phosphorylated time by the phosphatase inhibitor okadaic acid (OA) in cell‐attached patches made from single isolated rabbit ventricular myocytes, using barium as the charge carrier. 2. At low concentrations (0.001‐1 microM), OA decreased the number of sweeps without openings, while open duration was not changed. However, when cells were pretreated by a membrane‐permeant cyclic AMP, 0.1 microM OA induced long‐lasting channel openings as well. 3. At high concentrations (10‐750 microM), OA additionally induced long‐lasting openings, resulting in open time distributions that were best fitted by two exponentials. 4. The durations of an available state (TS) and an unavailable state (TF) were estimated by the numbers of non‐blank sweeps per run and blank sweeps per run by applying repetitive 45 ms steps at 2 Hz to 0 mV from holding potentials of ‐80 mV. TS was well fitted by an exponential curve, of which the time constant was increased from 0.67 to 1.60 sweeps by 0.1 microM OA, while TF was 0.347 sweeps and remained unchanged. 5. OA activated brief openings and long‐lasting, wide openings in a concentration‐dependent manner. Namely, we find different dose‐response relationships for the two kinetic effects of increased opening probability (mode 1) and prolongation of opening (mode 2). This behaviour suggests that there are at least two modulatory phosphorylation sites that are dephosphorylated by different phosphatases.
Differential expression of sodium channels in acutely isolated myelinating and non‐myelinating Schwann cells of rabbits.
Authors: Chiu S Y
Published: December 2014

1. Single channel recordings were made of voltage‐sensitive sodium channels in outside‐out patches excised from the cell body region of Schwann cells. The cells were freshly isolated from sciatic nerves of 10‐week‐old rabbits and both myelinating and non‐myelinating Schwann cells were visually identified for recordings. 2. Sodium channel activities were observed in approximately 75% of patches (n = 41) obtained from cell bodies of non‐myelinating Schwann cells. In contrast, sodium channels were not observed in patches (n = 78) obtained from cell bodies of myelinating Schwann cells. 3. Transection of the sciatic nerves and allowing Wallerian degeneration to occur for 5‐11 days in vivo prior to recording resulted in the appearance of sodium channel activities in approximately 30% of the patches (n = 33) obtained from the cell body of the myelinating cells. 4. It is interesting that although immunocytochemical and saxitoxin binding experiments indicate the clear presence of sodium channels in the plasmalemma of myelinating Schwann cells (both at the cell body and at the paranodal region), the present study suggests that these channels are absent from the soma region of normal myelinating Schwann cells.
Long‐term modulation of the exercise ventilatory response in goats.
Authors: Martin P A , Mitchell G S
Published: December 2014

1. To test the hypothesis that repeated associations of exercise and increased respiratory dead space elicit mechanisms that augment future ventilatory responses to exercise alone, experiments were conducted on normal adult goats familiarized with experimental procedures. 2. Measurements of ventilation, arterial blood gases and CO2 production were made at rest, during mild steady‐state exercise (4 km h‐1; 5% grade) and with increased dead space at rest in seven goats before and after training. In Series I experiments, training consisted of fourteen to twenty exercise trials explicitly paired with increased dead space (0.8 l) over 2 days. Increased dead space predominantly represents a CO2 chemoreceptor stimulus with only mild hypoxic stimulation. Post‐training measurements were made 1‐6 h and 1 week after training was completed. 3. The same goats repeated a slightly modified protocol several months later (Series II; 6 trials per day for 4 days) to determine if responses were both repeatable and reversible, and to investigate training effects on dynamic ventilatory responses at the onset of exercise. 4. In Series I experiments, resting minute ventilation and breathing frequency were elevated 1‐6 h post‐training compared to baseline (44 and 74% respectively), whereas resting tidal volume decreased (14%). One week post‐training, resting values had returned to baseline. Series II training had no significant effects on resting measurements. 5. Relative to baseline, arterial partial pressure of CO2 (Pa,CO2) values decreased significantly more from rest to exercise 1‐6 h post‐training in both Series I (2.7 +/‐ 0.2 vs. 1.8 +/‐ 0.9 mmHg) and Series II (3.4 +/‐ 0.6 vs. 2.0 +/‐ 0.6 mmHg). The exercise ventilatory response increased 25‐28% 1‐6 h post‐training (both series), largely due to a greater exercise frequency response, but returned to baseline 1 week post‐training. Training had no effect on ventilatory responses to CO2 at rest, suggesting that decreases in CO2 chemoreceptor responsiveness did not cause the greater exercise ventilatory response. Model estimates indicate that the net feedforward exercise ventilatory stimulus was increased 40‐50% by training. 6. Training had no discernable effects on ventilatory dynamics at the onset of exercise. However, post‐training differences in Pa,CO2 regulation and ventilation were established early in exercise, prior to steady state. 7. Collectively, these experiments suggest a previously unsuspected degree of repeatable and reversible plasticity in the control system subserving the exercise ventilatory response. Such plasticity may contribute to the development of normal exercise hyperpnoea and to adaptive responses of the ventilatory control system in adult animals.
Task‐related changes in the effect of magnetic brain stimulation on spinal neurones in man.
Authors: Nielsen J , Petersen N , Deuschl G , Ballegaard M
Published: December 2014

1. The effect of magnetic stimulation of the human motor cortex on the excitability of soleus, tibialis anterior and flexor carpi radialis motoneurones was investigated by H reflex testing in ten healthy subjects. 2. At rest, an early facilitation of the flexor capri radialis and tibialis anterior H reflexes was always seen, whereas a similar early facilitation of the soleus H reflex was seen in only two out of seven subjects. For all three motoneuronal pools the facilitation was curtailed 1‐5 ms later by an inhibition which lasted for another 3‐4 ms. In five subjects an inhibition without any evidence of an earlier facilitation was seen for the soleus H reflex. 3. The intensity of the magnetic stimulation was subsequently decreased so that it had no effect on the H reflex at rest. When the subject then performed a voluntary agonist contraction a facilitatory effect with an early onset and a duration of 20‐25 ms was observed for all three muscles. When the subject performed a voluntary antagonist contraction an inhibition was seen for the soleus H reflex with an onset 1‐3 ms later than the facilitation. This is interpreted as resulting from the excitation by the magnetic stimulus of corticospinal neurones voluntarily activated in relation to the given motor task. 4. The initial part of the facilitation was significantly smaller during co‐contraction of both agonists and antagonists than during isolated agonist contraction. 5. Whereas the early part of the facilitation always occurred during plantarflexion when the H reflex was conditioned by magnetic stimulation, this was never the case when it was conditioned by electrical stimulation of the cortex with the stimulus regimes used in these experiments. 6. It is suggested that the early part of the facilitation observed during agonist contraction is caused by activation of cortico‐motoneuronal cells projecting to the agonist motoneuronal pool and that the inhibition observed during antagonist contraction is caused by activation of corticospinal cells projecting both to the antagonist motoneuronal pool and Ia inhibitory interneurones to the agonist motoneuronal pool. The smaller size of the earliest part of the facilitation observed during co‐contraction in relation to agonist contraction suggests a different cortical control of the two tasks.
Interstitial glucose and lactate balance in human skeletal muscle and adipose tissue studied by microdialysis.
Authors: Rosdahl H , Ungerstedt U , Jorfeldt L , Henriksson J
Published: December 2014

1. Microdialysis was used to gain insight into the substrate exchanges in the interstitial space of skeletal muscle and adipose tissue. Probes were inserted in the quadriceps femoris muscle and para‐umbilical subcutaneous adipose tissue of thirteen subjects and microdialysis was performed at different flow rates (1‐4 microliters min‐1) and during changes in tissue blood flow. 2. When ethanol (5 mM) is included in the perfusion solution, the ethanol clearance from the probe is a measure of tissue blood flow. Blood flow changes induced by adenosine or vasopressin perfusion, by exercise or by circulatory occlusion resulted in ethanol clearance values of 69‐139% of the basal level. The ethanol clearance was higher in skeletal muscle than in adipose tissue (32‐62%, P < 0.001), a difference compatible with a higher blood flow in muscle tissue. 3. The fraction of the interstitial glucose concentration that was recovered with the microdialysis was similar in skeletal muscle (the absolute values being 1.70 +/‐ 0.14 mM at 1 microliter min‐1 and 0.59 +/‐ 0.05 mM at 4 microliters min‐1) and adipose tissue (1.89 +/‐ 0.20 mM at 1 microliter min‐1; 0.54 +/‐ 0.05 mM at 4 microliters min‐1) and correlated inversely with the tissue ethanol clearance, both in the basal state and during changes in tissue blood flow (muscle: r = ‐0.56 to ‐0.67; adipose tissue r = ‐0.72 to ‐0.95). Coefficients of variation were 6‐8% (glucose) and 11‐16% (lactate) and were similar during isometric exercise. The reproducibility of the technique (comparison of two contralateral probes; perfusion flow rate 4 microliters min‐1) was 5.3‐8.3% (ethanol) and 23.9‐20.8% (glucose) in muscle (n = 6) and adipose tissue (n = 4) respectively. 4. The skeletal muscle dialysate lactate concentration (1 microliter min‐1: 1.16 +/‐ 0.2 mM) was higher than in adipose tissue (0.76 +/‐ 0.08 mM, P < 0.05), where the absolute amount of lactate that could be removed from the tissue (at 4 microliters min‐1) was only half of that in skeletal muscle (0.8 +/‐ 0.11 vs. 1.76 +/‐ 0.23 nmol min‐1, P < 0.05). The dialysate lactate level was not affected in either tissue by large changes in the interstitial glucose concentration indicating that in neither tissue is blood glucose a significant source of lactate formation. 5. The blood flow effects on the dialysate glucose concentration are the likely consequence of probe glucose drainage artificially shifting the balance between the supply and consumption of interstitial glucose.(ABSTRACT TRUNCATED AT 400 WORDS)
Activation and inactivation of the bursting potassium channel from fused Torpedo synaptosomes.
Authors: Edry‐Schiller J , Rahamimoff R
Published: December 2014

1. The voltage dependence of the bursting potassium channel in fused synaptosomes from Torpedo electric organ was studied in vitro, using the inside‐out and the cell‐attached configurations of the patch clamp technique. 2. The patch of membrane was held at various holding potentials (‐140 to ‐50 mV) and then stepped to test potentials (‐50 to +40 mV) for periods ranging from 5 to 300 ms. Each potential step was repeated 200‐600 times. After subtraction of the capacitative transients and the leakage currents, an ensemble‐averaged current was obtained. This ensemble current showed a marked activation upon depolarization, followed by an inactivation. 3. The activation of the bursting potassium channel is markedly dependent on the voltage step. Activation was detected at voltages positive to ‐50 mV. The peak of the ensemble current increases with the degree of depolarization, while the time to the peak decreases. With progressively larger depolarization, there is a shortening in the delay between the onset of the voltage step and the opening of the bursting potassium channels. 4. The inactivation phase of the ensemble current could be described adequately in most of the experiments, as a single exponential decay to a steady‐state inactivation level. The time constant of inactivation was not markedly voltage dependent. 5. Single channel analysis of the inactivation reveals that it is due to a reduction in the number of channel openings and not due to changes in single channel current amplitude or channel mean open time along the pulse. 6. The holding potential has a marked effect on the peak amplitude of the ensemble current, indicating that hyperpolarization removes inactivation and depolarization induces it. The peak amplitude vs. voltage relation was fitted by the Boltzmann equation. The half‐maximal inactivation was ‐105.2 +/‐ 5.8 mV (mean +/‐ S.E.M.), suggesting that at the resting potential a substantial fraction of the bursting potassium channels is in an inactivated state. 7. Two‐pulse experiments show that the recovery from inactivation is a slow process which lasts well over 1 s. 8. High‐frequency stimulation (20‐66.7 Hz) by 5 ms pulses produces a progressive decline in the peak ensemble current amplitude. The decline is larger at higher stimulation frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)
Stable co‐expression of calcium channel alpha 1, beta and alpha 2/delta subunits in a somatic cell line.
Authors: Welling A , Bosse E , Cavalié A , Bottlender R , Ludwig A , Nastainczyk W , Flockerzi V , Hofmann F
Published: December 2014

1. The high‐voltage‐activated L‐type calcium channel is a multi‐protein complex of alpha 1, alpha 2/delta, beta and gamma subunits. The alpha 1 subunit contains the voltage‐dependent calcium‐conducting pore. Chinese hamster ovary (CHO) cells were stably transfected with the complementary DNA of the alpha 1, beta and alpha 2/delta subunits. These subunits were not detected in wild‐type CHO cells. 2. The alpha 1 (CaCh2b) subunit itself directed the expression of functional calcium channels which bound calcium channel blockers and showed voltage‐dependent activation and inactivation. 3. The co‐expression of the alpha 1 subunit with the beta subunit (CaB1 gene) enhanced the density of the dihydropyridine binding sites 2‐ to 3‐fold and increased dihydropyridine‐sensitive barium inward currents (IBa) up to 3.5‐fold from ‐13.3 microA/cm2 (alpha 1 subunit) to ‐46.7 microA/cm2 (alpha 1 and beta subunits). 4. Co‐expression of the beta subunit did not change the sensitivity of IBa towards dihydropyridines, but accelerated current activation and inactivation and shifted the half‐maximal steady‐state activation and inactivation to slightly more hyperpolarizing potentials. 5. The co‐expression of the alpha 2/delta subunit together with alpha 1 and beta subunits accelerated the inactivation kinetics of the channel without a major effect on the other parameters. 6. These results indicate that the beta and alpha 2/delta subunit interact with the alpha 1 subunit and modulate thereby the properties of the alpha 1 subunit‐dependent inward current.
Photocurrents in retinal rods of pigeons (Columba livia): kinetics and spectral sensitivity.
Authors: Palacios A G , Goldsmith T H
Published: December 2014

1. Membrane photocurrents were recorded from outer segments of isolated retinal rods of pigeons (Columba livia), the first such measurements on the photoreceptors of a bird. The amplitude of the response to 20 ms flashes of narrow wavelength bands of light increases linearly with intensity at low photon fluxes and saturates at higher intensities. The maximum (saturating) photocurrent observed in forty‐nine rod cells was 50 pA. Larger responses with less variability in the intensity for half‐maximal responses were observed when the physiological saline contained 20 mM bicarbonate (in addition to Hepes buffer). 2. The dependence of peak amplitude on intensity is well fitted by an exponential function; it is usually less well fitted by the Michaelis‐Menten (Naka‐Rushton) equation. 3. In the presence of bicarbonate, the average sensitivity of pigeon rods to dim flashes was 0.56 pA photon‐1 microns ‐2. The effective collecting area per photon was 1.8 microns 2. About 83 +/‐ 26 (mean +/‐ S.D.) photoisomerizations were required for a half‐saturating response. 4. The response kinetics of rods to dim flashes can be reasonably well described by a series of four to five either Poisson or independent filters. The time to peak, measured from the mid‐point of a 20 ms flash, was 319 +/‐ 83 ms (mean +/‐ S.D.). The integration time of the response was 851 +/‐ 86 ms (mean +/‐ S.D.) with bicarbonate present and 572 +/‐ 126 ms in the absence of bicarbonate. The responses of pigeon rods appear to be slower than those of mammals at the same temperature. The fraction of current suppressed by a single photoisomerization is smaller in pigeon than in mammalian rods by a factor of at least two. 5. The spectral sensitivity function was measured between 680 and 330 nm. The maximum at about 505 nm (range 497‐508 nm) corresponds to the alpha‐band of a vertebrate rhodopsin and agrees with previous behavioural measurements of scotopic sensitivity of pigeons as well as the absorption spectrum of extracts of pigeon rhodopsin. There was no pronounced beta‐band in the near‐ultraviolet wavelengths.
Activation of internodal potassium conductance in rat myelinated axons.
Authors: David G , Barrett J N , Barrett E F
Published: December 2014

1. Voltage changes associated with currents crossing the internodal axolemma were monitored using a microelectrode inserted into the myelin sheath (peri‐internodal region) of rat phrenic nerve fibres. This microelectrode was also used to change the potential and the ionic environment in the peri‐internodal region. 2. Following stimulation of the proximal nerve trunk, the peri‐internodal electrode recorded a positive‐going action potential whose amplitude increased (up to 75 mV) with increasing depth of microelectrode penetration into the myelin. The resting potential recorded by the peri‐internodal electrode remained within 4 mV of bath ground. 3. Confocal imaging of fibres injected peri‐internodally with the fluorescent dye Lucifer Yellow revealed a staining pattern consistent with spread of dye throughout the myelin sheath of the injected internode. 4. After ionophoresis of K+ (but not Na+) into the peri‐internodal region, the action potential was followed by a prolonged negative potential (PNP) lasting hundreds of milliseconds to several seconds. The duration of the PNP increased as the frequency of stimulation decreased. PNPs could also be evoked by sub‐threshold depolarization of the internodal axolemma with peri‐internodally applied current pulses. In the absence of action potentials or applied depolarization PNPs sometimes appeared spontaneously. 5. Peri‐internodal application of Rb+ also produced evoked and spontaneous PNPs. These PNPs had longer durations (up to 20 s) than those recorded from K(+)‐loaded internodes. 6. Spontaneous action potentials sometimes appeared during the onset of the PNP, suggesting that PNPs are associated with depolarization of the underlying axon. 7. Passage of current pulses during the PNP demonstrated that the PNP is associated with an increased conductance of the pathway linking the peri‐internodal recording site to the bath. At least part of this conductance increase occurs across the internodal axolemma, since peri‐internodally recorded action potentials evoked during the PNP had larger amplitudes than those evoked before or after the PNP. 8. PNPs were suppressed by tetraethylammonium (TEA, 10‐20 mM) and by 4‐aminopyridine (1 mM). 9. These results suggest that the PNPs recorded in K(+)‐ or Rb(+)‐loaded myelin sheaths are produced by a regenerative K+ or Rb+ current that enters the internodal axolemma via K+ channels opened by action potentials or subthreshold depolarizations. 10. When normal extracellular [K+] was preserved (by using Na+ rather than K+ salts in the peri‐internodal electrode), action potentials recorded within the myelin sheath were instead followed by a brief, positive after‐potential that was inhibited by TEA.(ABSTRACT TRUNCATED AT 400 WORDS)
Highly co‐operative Ca2+ activation of intermediate‐conductance K+ channels in granulocytes from a human cell line.
Authors: Varnai P , Demaurex N , Jaconi M , Schlegel W , Lew D P , Krause K H
Published: December 2014

1. To study Ca(2+)‐activated K+ currents in dimethyl sulphoxide (DMSO)‐differentiated HL‐60 cells (HL‐60 granulocytes), we have combined the patch clamp technique with microfluorimetric measurements of the cytosolic free Ca2+ concentration ([Ca2+]i). 2. Elevations of [Ca2+]i induced by the receptor agonist N‐formyl‐L‐methionyl‐L‐phenylalanine (f‐MLP), by cellular spreading or by the Ca2+ ionophore ionomycin, activated whole‐cell currents. The kinetics of the current elevations closely paralleled the kinetics of the elevations in [Ca2+]i. Cellular spreading induced oscillations in [Ca2+]i and parallel oscillatory changes in the amplitude of the recorded currents. 3. The reversal potential of the Ca(2+)‐activated current was a function of the extracellular K+ concentration (56.1 mV per log [K+]), demonstrating that the underlying conductance was selective for K+. 4. The current was blocked by charybdotoxin, but insensitive to apamin. 5. The whole‐cell current was inwardly rectifying. No time‐dependent activation or inactivation of the current could be observed within the range of voltages tested (‐100 to +100 mV). 6. The dependence of the current amplitude on the measured [Ca2+]i revealed a half‐maximal activation at approximately 350 nM [Ca2+]i, and a highly co‐operative activation by [Ca2+]i with an apparent Hill coefficient of approximately 8. Neither the half‐maximal activation by [Ca2+]i nor the apparent Hill coefficient depended on the voltage, and they were identical for Ca2+ elevations caused by the ionophore and the receptor agonist. 7. Analysis of Ca(2+)‐activated single‐channel events in cell‐attached recordings revealed an inwardly rectifying K+ channel with a slope conductance of 35 pS. Fluctuation analysis of the Ca(2+)‐activated whole‐cell current suggested an underlying single‐channel conductance of a similar size (28 pS). 8. In summary, we describe a charybdotoxin‐sensitive, intermediate‐conductance Ca(2+)‐activated K+ channel in HL‐60 granulocytes. The characteristics of the Ca2+ activation of this current (i.e. sensitivity to submicromolar [Ca2+]i, high co‐operativity and voltage independence) are similar to the Ca2+ activation of the apamin‐sensitive small‐conductance K+ channel. Our results also suggest that [Ca2+]i elevations are the predominant, if not the only, activators of this channel during physiological stimulation of HL‐60 granulocytes.
Respiration‐synchronous fluctuations in stroke volume, heart rate and arterial pressure in humans.
Authors: Toska K , Eriksen M
Published: December 2014

1. Simultaneous recordings of beat‐to‐beat left cardiac stroke volume (SV, pulsed ultrasound Doppler), mean arterial pressure (MAP) and heart rate (HR) were obtained in ten healthy young adults during spontaneous respiration at supine rest, before and after cholinergic blockade by atropine (0.035 mg kg‐1). 2. Respiration‐synchronous fluctuations in SV, HR, cardiac output (CO) and MAP were quantified by spectral analysis of the recordings of each of these variables. 3. Before atropine administration, respiration‐synchronous fluctuations in HR and SV were prominent. The changes in HR and SV were inversely related and variation in SV was the main source of respiratory variability in CO. Respiration‐synchronous fluctuations in MAP were mainly caused by variations in CO. 4. After cholinergic blockade, respiratory HR variations were eliminated, whereas the respiratory fluctuations in SV persisted. The fluctuations in CO and MAP increased. In this situation, mechanically induced variations in SV were not counteracted by inverse HR fluctuations and the influence on CO thus increased. 5. The main source of respiratory fluctuations in MAP in supine humans is thus variation in SV, while inverse, vagally mediated HR variations tend to reduce the fluctuations in CO and MAP.
A chloride current associated with swelling of cultured chick heart cells.
Authors: Zhang J , Rasmusson R L , Hall S K , Lieberman M
Published: December 2014

1. Cultured chick heart cells challenged by hyposmotic stress underwent regulatory volume decrease (RVD) that was attenuated by prior depletion of intracellular chloride. 2. During hyposmotic swelling, cell aggregates experienced an initial increase in spontaneous contractile activity followed by eventual quiescence. Conventional microelectrode studies revealed an underlying increase in spontaneous electrical activity, followed by a sustained depolarization beyond threshold. 3. Whole‐cell patch clamp studies, with K+ currents blocked, indicated that exposure of cells to hyposmotic solution (NaCl reduction) resulted in a rapid osmotic swelling followed by a substantial increase in whole‐cell conductance which persisted for the duration of hyposmotic exposure and was almost completely reversed on return to isosmotic bath solution. 4. For a variety of Cl‐ concentrations, the reversal potentials (Erev) of the measured swelling‐activated current closely followed the calculated Cl‐ equilibrium potential (ECl) with a linear regression slope of 0.82. When estimated by the Nernst equation, the relationship between Erev and the [Cl‐]i/[Cl‐]o ratio fitted well with a slope of 51 mV per decade change in the concentration ratio, consistent with a Cl(‐)‐selective conductance. 5. The permeability ratios of this swelling‐activated conductance to chloride, methanesulphonate (MSA) and aspartate (Asp) were calculated as PCl:PMSA:PASP = 1:0.36:0.02, with the ion selectivity sequence of Cl‐ > MSA‐ >> Asp‐, which suggests the swelling‐activated conductance is slightly permeable to other anions. 6. Application of a Cl‐ channel blocker, diphenylamine‐2‐carboxylate (DPC, 200 microM), substantially suppressed the swelling‐activated current without shifting the Erev of this current. The effect of DPC was independent of membrane potential. 7. This evidence demonstrates that hyposmotic swelling of cultured chick heart cells activates a channel‐mediated Cl‐ conductance which may be associated with the integrated response of volume‐regulatory mechanisms.
Inactivating ‘ball’ peptide from Shaker B blocks Ca(2+)‐activated but not ATP‐dependent K+ channels of rat skeletal muscle.
Authors: Beirão P S , Davies N W , Stanfield P R
Published: December 2014

1. Shaker B inactivating ‘ball’ peptide is shown to produce no detectable block of ATP‐dependent K+ channels of rat skeletal muscle fibres at concentrations up to 300 microM or membrane potentials up to +30 mV. 2. The peptide does produce a voltage‐dependent block of large‐conductance Ca(2+)‐activated K+ channels at lower concentrations (K1 = 55 microM at 0 mV). An appropriate point mutation (L7E) abolishes block. 3. Mean open times, corrected for missed closures, are little affected by the blocking peptide, but burst durations are substantially reduced. 4. The inactivating peptide increases occupancy of substates, whose amplitudes are 0.27 and 0.64 of fully open.
NMDA and non‐NMDA receptors may play distinct roles in timing mechanisms and transmission in the feline respiratory network.
Authors: Pierrefiche O , Foutz A S , Champagnat J , Denavit‐Saubié M
Published: December 2014

1. Activation of N‐methyl‐D‐aspartate (NMDA) glutamate receptors in the brainstem network of respiratory neurones is required to terminate inspiration in the absence of lung afferents, but it is not required in the inspiratory motor act of lung inflation. In the present study we examined the involvement of non‐NMDA ionotropic glutamate receptors in these two mechanisms in the adult mammal. 2. Adult cats were either decerebrated or anaesthetized with sodium pentobarbitone, paralysed and ventilated. Inspiratory motor output was recorded from the phrenic nerve and central respiratory activity from neurones in the bulbar ventral respiratory group. 3. In decerebrate vagotomized cats, ionophoretic application of 2,3‐dihydroxy‐6‐nitro‐7‐sulphamoylbenzo(F)quinoxaline (NBQX) onto single respiratory neurones decreased their spontaneous discharge rate and abolished the excitatory effect of exogenously applied (RS) alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionic acid (AMPA) but not NMDA. 4. In these animals, intravenous infusion (12 mg kg‐1) of the non‐NMDA receptor blockers GYKI 52466 (1‐(4‐aminophenyl)‐4‐methyl‐7,8‐methylene‐dioxy‐5‐H‐2,3‐benzodi aze pine) or NBQX: (1) decreased (in 10/15 cats) or abolished (in 5/15 cats) the inspiratory‐related discharge of the phrenic nerve; (2) did not prolong the inspiratory phase; (3) reduced or abolished the spontaneous discharge of respiratory neurones; and (4) profoundly decreased the excitatory effects of AMPA but not NMDA ionophoresed onto these neurones. When both the phrenic nerve and the recorded respiratory neurone were silenced, neuronal excitation by ionophoretic application of NMDA first revealed a subthreshold respiratory modulation without lengthening of the inspiratory phase, then respiratory modulation became undetectable. 5. Additional blockade of NMDA receptors by a small dose (0.15 mg kg‐1) of dizocilpine (MK‐801), abolished the phrenic nerve activity which persisted after NBQX (apnoea), but the discharge or the subthreshold modulation of the bulbar respiratory neurones showed a lengthening of the inspiratory phase (apneusis). 6. Elevation of FA,CO2 increased or re‐established phrenic nerve discharges after blockade of non‐NMDA receptors or of both NMDA and non‐NMDA receptors. 7. Small doses of NBQX or GYKI 52466 induced apnoea in five of five cats anaesthetized with sodium pentobarbitone. 8. In decerebrate animals with intact vagi, GYKI 52466 and NBQX depressed the Hering‐Breuer expiratory‐lengthening reflex. 9. The results suggest that: (1) there is a specialization of different classes of glutamate receptors participating in timing mechanisms and transmission within the mammalian respiratory network. Neural transmission predominantly involves activation of non‐NMDA receptors, acting in synergy with NMDA receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of sleep on the tonic drive to respiratory muscle and the threshold for rhythm generation in the dog.
Authors: Horner R L , Kozar L F , Kimoff R J , Phillipson E A
Published: December 2014

1. The present study was designed to determine the effect of sleep on the tonic output to respiratory muscle and on the level of chemical respiratory stimulation required to produce rhythmic respiratory output. 2. Chronically implanted electrodes recorded expiratory (triangularis sterni) and inspiratory (diaphragm and parasternal intercostal) electromyographic (EMG) activities in three trained dogs during wakefulness and sleep. The dogs were mechanically hyperventilated via an endotracheal tube inserted into a permanent tracheostomy. During the studies, a cold block of the cervical vagus nerves was maintained to avoid the complicating effects of vagal inputs on respiratory drive and rhythm. 3. During wakefulness, steady‐state hypocapnia (partial pressure of CO2, PCO2 = 30 mmHg) abolished inspiratory EMG activity, resulting in apnoea, but the expiratory muscle became tonically active. Compared to wakefulness, the level of the tonic expiratory EMG activity was decreased in non‐REM (non‐rapid eye movement) sleep (median decrease = 34%, P = 0.005) and was further decreased in REM sleep (median decrease = 78%, P < 0.0001). During REM sleep, the tonic expiratory EMG activity was highly variable (mean coefficient of variation = 39% compared to 7% awake, P < 0.0001) and in some periods of REM, bursts of inspiratory EMG activity and active breathing movements were observed despite the presence of hypocapnia. 4. During constant mechanical hyperventilation, progressive increases in arterial PCO2 (in hyperoxia) were produced by rebreathing. Measurement of the CO2 threshold for the onset of spontaneous breathing showed that this threshold was not different between wakefulness and non‐REM sleep (mean difference = 0.1 mmHg from paired observations, 95% confidence interval for the difference = ‐1.0 to +1.1 mmHg, P = 0.898). 5. The results show that sleep reduces the tonic output to respiratory muscles but does not increase the CO2 threshold for the generation of rhythmic respiratory output. These observations suggest that changes in the tonic drives to the respiratory motoneurones may be a principal mechanism by which changes in sleep‐wake states produce changes in respiratory output.
Phosphorylation and dephosphorylation modulate a Ca(2+)‐activated K+ channel in rat peptidergic nerve terminals.
Authors: Bielefeldt K , Jackson M B
Published: December 2014

1. Ca(2+)‐activated K+ channels regulate the excitability of many nerve terminals. A Ca(2+)‐activated K+ channel present in the membranes of rat posterior pituitary nerve terminals runs down following the formation of excised patches. This run‐down process reflects enzymatic dephosphorylation. 2. Both Mg‐ATP and the protein phosphatase inhibitor okadaic acid prevented run‐down of channel activity in excised patches. The okadaic acid sensitivity suggests that run‐down resulted from dephosphorylation by a type 1 protein phosphatase. 3. Guanosine 5'‐O‐(3‐thiotriphosphate) (GTP gamma S) accelerated run‐down by accelerating okadaic acid‐sensitive dephosphorylation. GTP gamma S had no effect on the activity of the protein kinase in these patches. These results suggest a direct coupling between a G‐protein and a protein phosphatase. 4. After run‐down, channel activity could be restored by Mg‐ATP; restoration depended on ATP hydrolysis, but did not require Ca2+ or a second messenger. Restoration of channel activity by ATP was blocked by staurosporine and 1‐(5‐isoquinolinylsulphonyl)‐3‐methylpiperizine, but not by more specific inhibitors of protein kinases. 5. Restoration of channel activity by phosphorylation was very sensitive to membrane potential; increasing the voltage by as little as 10 mV could dramatically enhance recovery. 6. Ca2+ and voltage acted synergistically to enhance phosphorylation; higher [Ca2+] permitted phosphorylation at more negative potentials. 7. During trains of high frequency stimulation under current clamp, action potentials were influenced by both the protein phosphatase and protein kinase, indicating that enzymatic modulation of channel gating occurs under physiological conditions. An important implication of these results is that voltage‐dependent phosphorylation could play a role in use‐dependent depression of secretion from nerve terminals.
Developmental changes in hypoxia‐induced catecholamine release from rat carotid body, in vitro.
Authors: Donnelly D F , Doyle T P
Published: December 2014

1. Developmental changes in free tissue catecholamine levels were studied using Nafion‐coated, carbon fibre electrodes placed in rat carotid bodies, in vitro. Simultaneously, single fibre chemoreceptor afferent activity was recorded from the sinus nerve. Five age groups were examined: 1, 2, 6, 10 and 20‐30 days of age. 2. Using fast‐scan voltammetry, similar current peaks were observed during exposure to exogenous dopamine and during superfusion with hypoxic saline. This suggests that changes in carbon fibre electrode current are due to an increase in free tissue catecholamines. 3. Baseline catecholamine levels were significantly less in the 1‐6 day age groups compared to 10 day and 20‐30 day rats. 4. During 1 min of hypoxia the peak concentration of tissue catecholamine was significantly less in the 1 day compared to the 2 day age groups, and these were less than in 10 day and 20‐30 day rats. 5. Peak nerve response during hypoxia increased with age from 4.5 +/‐ 0.6 Hz in the 1 day to 10.5 +/‐ 1.6 Hz in the 6 day and to 15.5 +/‐ 2.2 Hz in the 20‐30 day rats. 6. We conclude that (1) resting free tissue catecholamine levels increase with age in the newborn period, (2) hypoxia causes enhanced catecholamine release, and (3) the magnitude of the release increases in the postnatal period as does the nerve activity.
A comparison of the effects of intracellular and extracellular pH on contraction in isolated rat portal vein.
Authors: Taggart M , Austin C , Wray S
Published: December 2014

1. The effects of changes in extracellular and intracellular pH on spontaneous contractile activity in isolated rat portal vein have been investigated. 2. Small strips of portal vein were loaded with the pH‐sensitive fluorophore carboxy‐SNARF and intracellular pH (pHi) and contraction were measured simultaneously at 37 degrees C. The tissue was superfused with oxygenated, Hepes‐buffered solutions at pH 7.4. Intracellular pH was altered by isosmotic substitution of weak acids or bases. External pH (pHo) was altered by addition of strong acid or base to the solution. 3. The mean resting value of pHi was 7.06 +/‐ 0.03 (n = 28). Alteration of pHi led to changes in spontaneous activity. Addition of butyrate (20 mM) reduced pHi by 0.18 +/‐ 0.01 pH units (n = 8). Decreasing pHi produced an early, brief increase in contractile activity followed by a longer lasting decrease or even abolition of contraction. 4. Addition of 20 mM trimethylamine or NH4Cl increased pHi by around 0.2 pH units and produced an early transient decrease in contractile activity followed by a later maintained increase, both in frequency and magnitude. Removal of base produced a rapid rebound decrease in pHi which was associated with a further transient increase in contractile activity followed by decreased activity. The effects of base on both pHi and contraction were concentration dependent over the range investigated (2.5‐30 mM). 5. Alteration of pHo produced a change in pHi in the portal vein. The pHi change was rapid compared to other non‐vascular cells (about 1 min to half‐maximal response).(ABSTRACT TRUNCATED AT 250 WORDS)
Expression of a tetrodotoxin‐sensitive Na+ current in cultured human retinal pigment epithelial cells.
Authors: Wen R , Lui G M , Steinberg R H
Published: December 2014

We observed a tetrodotoxin (TTX)‐sensitive Na+ current in cultured fetal and adult cells of the human retinal pigment epithelium (RPE), but not in any freshly isolated fetal (n = 54) or adult (n = 47) cells, using the whole‐cell version of the patch‐clamp technique. A similar current was found in cultured, but not in freshly isolated, adult monkey RPE cells. The rapid activation and inactivation of this current resembled that of the voltage‐dependent Na+ current of excitable cells. The voltage dependence of inactivation followed a Boltzmann function with half‐maximal inactivation at ‐52.1 +/‐ 4.8 mV (n = 9), thus classifying this current as ‘neuronal’ in type. Recovery from inactivation followed a single exponential function with a time constant of 12.0 +/‐ 1.4 ms (n = 5) at ‐100 mV. The current was very sensitive to the Na+ channel blocker TTX, with a half‐inhibition concentration of 1.87 +/‐ 0.37 nM (n = 5). Of special interest are the findings that current density was high when cells were rapidly proliferating and had lost their melanin pigment, and that the density declined after the cells reached confluence and repigmented. This pattern of current expression was consistently found in cells cultured with three different protocols, including a serum‐free medium, indicating that serum was not necessary for its expression. We hypothesize that expression of this Na+ current in culture is regulated by an intrinsic programme related to cell differentiation. It may represent a tendency of proliferating RPE cells to dedifferentiate towards a more embryonic and neuroepithelial phenotype. Similar expression of Na+ current might occur in vivo when RPE cells proliferate, as in wounding.
The role of ATP in non‐adrenergic sympathetic vascular control of the nasal mucosa in anaesthetized cats and dogs.
Authors: Lacroix J S , Ulman L G , Potter E K
Published: December 2014

1. In anaesthetized cats and dogs, local intra‐arterial injection of noradrenaline and alpha, beta‐methylene adenosine 5'‐triphosphate (mATP) reduced both nasal arterial blood flow and nasal mucosal volume (a measure of capacitance vessel function). The responses to mATP were not modified by pretreatment with the adrenoceptor antagonists phentolamine and propranolol or the purinoceptor antagonist suramin. The vascular effects of noradrenaline were not altered by suramin, but were virtually abolished by adrenoceptor antagonists. 2. After adrenoceptor blockade, frequency‐dependent reductions in nasal arterial blood flow with sympathetic nerve stimulation were reduced by 25 and 39% in cats and dogs, respectively; whereas the volume response was reduced by 56% in cats and 54% in dogs. The remaining non‐adrenergic sympathetic nerve‐evoked vascular responses were not influenced by suramin. 3. During desensitization to mATP induced by local intra‐arterial infusion for 5 min, the remaining non‐adrenergic nasal blood flow and volume responses to sympathetic nerve stimulation were reduced in the dog but not in the cat. 4. It is suggested that both adrenergic and non‐adrenergic mechanisms are involved in the sympathetic control of the nasal mucosa vascular bed of both species. Since desensitization to mATP markedly reduces the remaining non‐adrenergic nasal vasoconstriction evoked by sympathetic nerve stimulation in the dog, ATP is a possible sympathetic mediator in the nasal vascular bed in this species.
Is presynaptic inhibition distributed to corticospinal fibres in man?
Authors: Nielsen J , Petersen N
Published: December 2014

1. A tendon tap of the biceps femoris tendon was found to evoke a depression of the soleus and tibialis anterior H reflexes with a duration of 300‐400 ms and with an onset at a conditioning‐test interval of 20‐30 ms. It is suggested that the depression is caused by presynaptic inhibition of the terminals of the Ia afferents mediating the reflexes. 2. This possibility was tested by a method in which the H reflex is facilitated by a monosynaptic Ia volley from the quadriceps muscle. The attenuation of this facilitation when another pathway is stimulated is probably caused by presynaptic inhibition of Ia afferents. It was shown that the biceps femoris tendon tap depressed the size of the femoral nerve‐induced facilitation of the soleus and tibialis anterior H reflexes. This suggests that the depression of the reflexes by the tendon tap was indeed caused by presynaptic inhibition. 3. To investigate whether the terminals of descending fibres were similarly susceptible to presynaptic inhibition, the stimulation of the femoral nerve was replaced by magnetic stimulation of the contralateral motor cortex. This stimulation has been shown to evoke a facilitation of the tibialis anterior and soleus H reflexes which (within its initial 0.5‐1 ms) is probably caused exclusively by direct monosynaptic projections from the cortex to the motoneurones. In contrast to the facilitation evoked by Ia afferents, the descending facilitation was not influenced by the biceps tendon tap. 4. Similarly, the monosynaptic peak in the post‐stimulus time histogram (PSTH) of single voluntarily activated tibialis anterior motor units evoked by stimulation of the common peroneal nerve was depressed by the tendon tap, whereas this was not the case for the presumed monosynaptic peak evoked by brain stimulation. 5. It is suggested that the tendon tap evoked presynaptic inhibition of the terminals of flexor as well as extensor Ia afferents terminating on both soleus and tibialis anterior motoneurones. In contrast, the tap failed to elicit any presynaptic inhibition of the terminals of descending fibres on the motoneurones. We suggest that descending pathways in general are free from the presynaptic control which attenuates peripheral input to motoneurones. Through modulation of presynaptic inhibition the brain may thus selectively hinder the access of peripheral feedback mechanisms to the motoneurones, while still maintaining control of the output from the spinal cord through direct and indirect projections to the motoneurones.
Increased hypoxic ventilatory sensitivity during exercise in man: are neural afferents necessary?
Authors: Pandit J J , Bergstrom E , Frankel H L , Robbins P A
Published: December 2014

1. The acute ventilatory response to 3 min periods of hypoxia (AHR) was examined in nine patients with clinically complete spinal cord transection (T4‐T7) during (a) rest and (b) electrically induced leg exercise (EEL). 2. EEL was produced by surface electrode stimulation of the quadriceps muscles so as to cause the legs to extend at the knee against gravity. End‐tidal PCO2 was held constant 1‐2 mmHg above resting values throughout both protocols. 3. On exercise, the average increase in metabolic CO2 production (VCO2 +/‐ S.E.M.) was 41 +/‐ 5 ml min‐1. Venous lactate levels did not rise with exercise. 4. Baseline euoxic ventilation did not increase significantly with EEL, but there was a consistent and highly significant increase in the ventilatory response to hypoxia during EEL (mean delta AHR +/‐ S.E.M. of 1.6 +/‐ 0.21 min‐1). 5. We conclude that an increase in hypoxic sensitivity during exercise can occur in the absence of volitional control of exercise and in the absence of afferent neural input from the limbs.