bluuebunny/crossref_metadata_2025 huggingface dataset:
Slowly inactivating potassium current in cultured bull‐frog primary afferent and sympathetic neurones.
Authors: Tokimasa T , Tsurusaki M , Akasu T
Published: December 2014

1. Cultured bull‐frog dorsal root ganglion cells were voltage clamped in the whole‐cell configuration. The cells were superfused with a nominally calcium‐free Ringer solution containing tetrodotoxin (3 microM), magnesium (10 mM), cobalt (1 mM), barium (2 mM), 4‐aminopyridine (3 mM) and caesium (2 mM). 2. Step depolarizations (10‐40 mV, 100‐300 ms) from a holding potential close to the rest (typically ‐70 mV) evoked an outward current (IK) followed by an outward tail current. The peak amplitude of the current was reduced to less than 10% by tetraethylammonium (30 mM). 3. IK developed to its peak in 200 ms at ‐30 mV. Tail currents reversed at potentials that changed according to the logarithm of the extracellular potassium concentrations. 4. Tail currents declined to the baseline according to an exponential function of time (tau congruent to 40 ms at ‐60 mV) and its reciprocal time constant increased e‐fold with a 13 mV hyperpolarization. 5. The current inactivated during sustained (1‐20 s) depolarizing pulses according to a single exponential function (tau congruent to 3 s). 6. The peak amplitude of IK at ‐30 mV was progressively increased as the holding potential was made more negative than ‐70 mV reaching the maximum with step depolarizations from ‐120 mV. Reversed phenomenon was observed as the holding potential was made less negative than ‐70 mV. 7. The removal of the steady‐state inactivation occurred along with a single exponential function and the time constant was decreased from 70 ms at ‐70 mV to 10 ms at ‐120 mV. 8. It is suggested that a slowly inactivating potassium current which we called IK in amphibian sensory neurones could be a class of a ‘delayed’ rectifier potassium current. A potassium current with properties indistinguishable from those which have been described for the sensory IK also occurred in cultured bull‐frog sympathetic neurones. 9. Forskolin (1‐30 microM) and 1,9‐dideoxy forskolin (10 microM) reduced the amplitude of IK by up to 85% but these actions were not mimicked by any of 8‐bromo‐cyclic AMP (1 mM), dibutyryl cyclic AMP (1 mM) and 3‐isobutyl‐1‐methylxanthine (1 mM). A hydrophilic forskolin analogue, 7‐O‐hemisuccinyl‐7‐deacetyl forskolin (10 microM), was about one‐tenth as potent as forskolin (10 microM).
Physiological characterization of two functional states in subpopulations of prolactin cells from lactating rats.
Authors: Lledo P M , Guerineau N , Mollard P , Vincent J D , Israel J M
Published: December 2014

1. Lactotroph cells from lactating female rat pituitary glands were dissociated, separated and enriched on a continuous gradient of bovine serum albumin at unit gravity. Two lactotroph subpopulations were observed in the light (F(3‐5)) and the heavy (F(7‐9)) fractions of the gradient. Both populations were maintained for at least 6 days in culture before experiments were performed. 2. Patch‐clamp recordings, in the whole‐cell mode, were performed on both lactotroph subpopulations in order to measure passive membrane properties and Ca2+ currents. Resting membrane potential as well as membrane capacitance values were found to be lower in light fraction cells. The two components of Ca2+ currents, called fast and slow deactivating (FD and SD) currents, were present with different proportions in each subpopulation; the ratio of current amplitudes, SD/FD, was 2.42 +/‐ 0.41 (n = 18) in light fraction cells and 1.17 +/‐ 0.27 (n = 17) in heavy fraction cells (P less than 0.02). 3. Reverse haemolytic plaque assay showed that in the light and heavy fractions, 68 and 47% of the lactotroph cells, respectively, were secreting. Population analysis of the plaque areas revealed a bimodal frequency distribution of plaque sizes consisting of small (1500 microns 2) and large plaques (3995 microns 2). A majority of light fraction cells produced large plaques whereas most of the heavy fraction cells produced small plaques. 4. Perifusion experiments performed on enriched prolactin cells showed that (1) basal prolactin (PRL) release was higher in light fraction than in heavy fraction cells, (2) the dopamine (10(‐8)M)‐induced inhibition of PRL release was greater in light fraction cells (86 +/‐ 15%) than in heavy fraction cells (41 +/‐ 21%), and (3) the thyrotrophin‐releasing hormone (TRH, 10(‐8)M)‐induced increase of PRL release was 150 +/‐ 60% in light fraction versus 330 +/‐ 82% in heavy fraction cells. 5. Current‐clamp recordings were performed using the intracellular technique. Lactotrophs were categorized according to their electrophysiological response following application of dopamine or TRH (both 10(‐8)M). In the light fractions, the majority of the cells tested were hyperpolarized by dopamine (68%), whereas only 7% were depolarized by TRH application. In the heavy fractions, most of the cells (63%) responded to TRH application, while only 13% were dopamine sensitive. 6. Cytosolic free Ca2+ concentration ([Ca2+]i) measurements with the fluorescent probe Indo‐1 revealed two lactotroph subtypes. Most cells in the light fractions (sixteen of twenty‐two tested cells) exhibited an unstable level of [Ca2+]i with values fluctuating between 114.1 +/‐ 34.3 and 221 +/‐ 50 nM (mean +/‐ S.D.). Application of dopamine or of the D2 receptor agonist RU 24213 (10(‐8)M) resulted in the disappearance of these fluctuations and in an accompanying decrease in basal [Ca2+]i level.(ABSTRACT TRUNCATED AT 400 WORDS)
Adaptation of glucose transport across rat enterocyte basolateral membrane in response to altered dietary carbohydrate intake.
Authors: Cheeseman C I , Harley B
Published: December 2014

1. The effect of changes in the carbohydrate content of the diet on D‐glucose transport across the basolateral membrane of rat enterocytes has been compared with alterations in transport across the brush‐border membrane. 2. Measurement of carrier‐mediated D‐glucose uptake across the jejunal brush border from animals fed a low‐ or high‐carbohydrate diet showed a change in the maximal rate of transport by 7 days which was maintained for 14 days. The low‐carbohydrate diet produced a progressive decline in uptake whereas the high‐carbohydrate diet increased the transport. There was no alteration in the apparent affinity constant as a result of the dietary manipulations and no discernible trend for changes in the passive permeability to glucose. 3. Transport of D‐glucose across the basolateral membrane was also affected by the dietary composition. After 7 days the maximal transport rate was greater in the animals fed the high‐carbohydrate diet. However, while this increase was maintained for 14 days, uptake into vesicles prepared after 2 weeks on the low‐carbohydrate diet showed a return to control levels. 4. A detailed analysis of the time course of these responses showed the effect on basolateral membrane transport to be inducible within 3 days of switching from the low‐ to the high‐carbohydrate diet and could be reversed within a similar period. 5. Kinetic studies using purified basolateral membrane vesicles confirmed that the change in transport was the result of an increase in the maximal transport rate. Analysis of cytochalasin B binding to these membranes showed a parallel change in the number of glucose‐inhibitable binding sites. 6. The component of the diet responsible for these changes was further investigated by replacing the glucose in the high‐carbohydrate food with galactose, fructose, mannose or 3‐O‐methylglucose. Only glucose and fructose produced any significant change in the transport across the basolateral membrane. 7. It is concluded that in response to changes in the carbohydrate content of the diet there are alterations in the capacity for glucose transport across the basolateral membrane of the enterocyte as well as in the brush‐border membrane. The change in transport across the basolateral membrane is best explained by an increase in the number of glucose carriers in this membrane.
A motor programme for the initiation of forward‐oriented movements in humans.
Authors: Crenna P , Frigo C
Published: December 2014

1. The EMG sequence activated before the initiation of a number of fast forward‐oriented voluntary movements was analysed quantitatively in normal subjects. 2. The sequence consisted of an initial inhibitory component directed to the soleus motor nucleus, followed by a second excitatory one directed to the tibialis anterior (TA). 3. The spectrum of functional utilization included motor tasks in which the prime movers are leg and thigh muscles (initiation of gait, rising on tip‐toes), thigh and trunk muscles (fast‐forward bending of the trunk, standing up) and upper‐limb muscles (forward throw or catch). 4. In a same motor task and across the different motor tasks, performed at various speeds, the latency of soleus inhibition and TA activation with respect to the onset of movement co‐varied according to a linear function, indicating a close temporal correlation between the two components. 5. In all the movements investigated, the earliest mechanical effect was a backward displacement of the centre of foot pressure in the sagittal plane. 6. Soleus inhibition alone and TA burst alone were each able to produce a backward displacement of the centre of foot pressure, but the effect was significantly slower after soleus inhibition. 7. The spatio‐temporal parameters of the sequence were modulated according to the pre‐existing postural conditions. For the gait initiation protocol, increasing initial forward leaning led to a decrease in the amplitude of soleus inhibition and the TA burst, and to a change in their relative time delays. Modulation was different on the two sides. We could define a postural boundary as the degree of forward leaning beyond which the full sequence is no longer called into action. 8. The spatio‐temporal parameters of the sequence were pre‐set according to the requirements of the forthcoming movement. In the gait initiation protocol, the amplitude and synchronization of the TA burst were directly correlated with velocity of movement, while the relative delay between soleus inhibition and TA activation was inversely correlated. Modulation on the two sides differed. We could define a velocity boundary as the velocity of movement below which the full sequence is no longer called into action. 9. We suggest that the EMG sequence described can be considered a motor programme that, through direct action on the position of the centre of foot pressure (the variable primarily controlled), will precisely adjust the configuration of forces external to the body, allowing the contraction of the prime mover(s) to interact appropriately with them for the production of a specific, forward‐oriented movement.
Role of excitatory amino acids in the generation and transmission of respiratory drive in neonatal rat.
Authors: Greer J J , Smith J C , Feldman J L
Published: December 2014

1. The involvement of excitatory amino acids in the generation and transmission of rhythmic respiratory drive was studied in an in vitro neonatal rat brain stem‐spinal cord preparation. The subclasses of excitatory amino acid receptors studied included: (i) N‐methyl‐D‐aspartate (NMDA) receptors, (ii) (R, S)‐alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid hydrobromide (AMPA) and kainate (non‐NMDA) receptors and (iii) 2‐amino‐4‐phosphonobutyric acid (AP‐4)‐sensitive receptors. Respiratory motoneurone population discharge was recorded from glossopharyngeal (IX), vagus (X), and hypoglossal (XII) cranial nerves, as well as cervical (C1‐C5) and thoracic (T2‐T5) spinal ventral roots. This activity is generated in the motoneurone pools that transmit respiratory drive to upper airway, accessory, diaphragm and intercostal muscles. Perturbations of motor nerve discharge were analysed after excitatory amino acid receptor antagonists or agonists were added to bathing solutions surrounding either the spinal cord or brain stem. The excitatory amino acid receptor antagonists included: (i) NMDA receptor antagonist (+)‐5‐methyl‐10,11‐dihydro‐5H‐dibenzo [a,d] cyclohepten‐5,10‐imin‐H‐maleate (MK‐801) and (ii) non‐NMDA receptor antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX). The agonists included: (i) NMDA, (ii) non‐NMDA receptor agonists AMPA and kainic acid. The effects of perturbations of AP‐4‐sensitive receptors with AP‐4, and of inhibiting excitatory amino acid uptake with dihydrokainic acid (DHK) were also studied. 2. Block of non‐NMDA receptors in the medulla by CNQX resulted in an antagonist concentration‐dependent decrease in the respiratory motoneuronal burst frequency. Non‐NMDA receptor activation with kainic acid or AMPA caused a concentration‐dependent increase in burst frequency, with competitive interactions with CNQX. 3. Inhibition of excitatory amino acid uptake in the medulla with DHK resulted in a reversible, dose‐dependent increase in respiratory frequency. A similar increase in respiratory frequency was induced by DHK when medullary NMDA receptors were blocked with MK‐801, confirming that endogenously released excitatory amino acids act at non‐NMDA receptors to modulate rhythm. 4. Non‐NMDA receptor block reduced and ultimately abolished the amplitude of integrated cranial and spinal respiratory motoneuronal discharge when added to the solution bathing the medulla and spinal cord, respectively. 5. NMDA receptor block in the medulla with MK‐801 did not perturb the spontaneous respiratory burst frequency, although bath application of NMDA produced a dose‐dependent increase in frequency, with non‐competitive interactions with MK‐801. MK‐801 also did not perturb the amplitude of cranial or bulbospinal premotoneurone discharge.(ABSTRACT TRUNCATED AT 400 WORDS)
Cyclic AMP relaxes swine arterial smooth muscle predominantly by decreasing cell Ca2+ concentration.
Authors: McDaniel N L , Rembold C M , Richard H M , Murphy R A
Published: December 2014

1. Our objective was to evaluate the mechanism of cyclic AMP‐dependent arterial smooth muscle relaxation. Cyclic AMP‐dependent relaxation has been proposed to result from either (a) a decrease in intracellular [Ca2+] or (b) a decrease in [Ca2+] sensitivity of myosin light chain kinase by protein kinase A‐dependent phosphorylation of myosin kinase. 2. We evaluated these proposed mechanisms by examining forskolin‐induced changes in aequorin‐estimated myoplasmic [Ca2+], [cyclic AMP], myosin phosphorylation and stress generation in agonist‐stimulated or KCl‐depolarized swine common carotid media tissues. 3. Forskolin, an activator of adenylyl cyclase, increased [cyclic AMP] and reduced [Ca2+], myosin phosphorylation and stress in tissues pre‐contracted with phenylephrine or histamine. This relaxation was not associated with an alteration of the [Ca2+] sensitivity of phosphorylation, nor the dependence of stress on phosphorylation. 4. Forskolin pre‐treatment attenuated, but did not abolish, agonist‐induced increases in [Ca2+] and stress. 5. These results suggest that cyclic AMP‐induced relaxation of the agonist‐stimulated swine carotid media is primarily caused by cyclic AMP‐mediated decreases in myoplasmic [Ca2+].
Modulation of noradrenaline‐induced membrane currents by papaverine in rabbit vascular smooth muscle cells.
Authors: Wang Q , Large W A
Published: December 2014

1. The modulation of noradrenaline‐induced membrane currents by papaverine was studied with the nystatin whole‐cell technique in freshly isolated rabbit ear artery and portal vein cells. 2. At a holding potential of ‐50 mV (in potassium‐free conditions), papaverine inhibited the Ca(2+)‐activated inward chloride current ICl(Ca) evoked by ionophoretic application of noradrenaline in rabbit portal vein cells in a concentration‐dependent (10(‐5)‐10(‐4) M) manner. 3. With potassium‐containing solutions (at 0 mV) 10(‐4) M‐papaverine reversibly abolished the Ca(2+)‐activated outward potassium current IK(Ca) induced by noradrenaline in both protal vein and ear artery cells. Occasionally, 10(‐4) M‐papaverine itself activated IK(Ca) before it abolished the response to noradrenaline. 4. Higher concentrations of papaverine (up to 10(‐3) M) always evoked both ICl(Ca) and IK(Ca) at ‐50 and 0 mV respectively, before it abolished these responses to noradrenaline in both ear artery and portal vein cells. In the presence of 10(‐3) M‐papaverine higher doses of noradrenaline evoked the non‐selective cation current in some portal vein cells. 5. In the presence of 10(‐2) M‐caffeine, which elicited both IK(Ca) and ICl(Ca), papaverine (10(‐3) M) failed to activate either current and 10(‐3) M‐papaverine reduced the caffeine‐induced IK(Ca) by 94%. In contrast, IK(Ca) induced by the calcium ionophore ionomycin was unaffected by papaverine. In Ca(2+)‐free, 1 mM‐EGTA external solutions, 10(‐3) M‐papaverine still induced IK(Ca) and blocked the response to noradrenaline. 6. The alpha 1‐adrenoceptor antagonist prazosin (5 x 10(‐8) M) completely blocked the noradrenaline‐induced IK(Ca) but currents evoked by papaverine (10(‐3) M) were unaffected by prazosin. 7. It was concluded that papaverine modulated noradrenaline‐induced membrane currents in vascular smooth muscle cells by releasing and depleting caffeine‐sensitive intracellular Ca2+ stores.
Radiation of phasic stretch reflex in biceps brachii to muscles of the arm in man and its restriction during development.
Authors: O'Sullivan M C , Eyre J A , Miller S
Published: December 2014

1. The phasic stretch reflex in biceps brachii has been recorded in 372 normal subjects aged from 31 weeks gestation to 55 years. The stimulus used was a brief mechanical pulse delivered by a hand‐held electromagnetic vibrator and the response was measured in the surface electromyogram. 2. The threshold for eliciting the reflex was low in the newborn and increased over the first 6 years to values corresponding to those of adults. 3. On the basis of timing it is concluded that the phasic stretch reflex has a monosynaptic component at all ages. 4. The surface electromyogram was also recorded in triceps brachii, pectoralis major, deltoid and hypothenar muscles. In some subjects evoking the phasic stretch reflex in biceps brachii resulted in short latency responses in these muscles, a phenomenon termed radiated response. 5. The probability of occurrence of radiated responses and their magnitudes were greatest at birth and decreased over 2‐4 years. 6. Experiments were performed to determine how far mechanical transmission of the stimulus to biceps through the tissues of the arm might account for the radiated responses in the other muscles studied. It was concluded that the responses observed in triceps brachii, pectoralis major, deltoid and hypothenar muscles, following vibration of the biceps tendon, are primarily due to the radiation of the activity carried in biceps muscle afferents to the alpha‐motoneurones of the respective muscles. 7. On the basis of timing it is concluded that in subjects below 2 years the radiated responses in the muscles studied have a monosynaptic component.
Extracellular volume decreases while cell volume is maintained by ion uptake in rat brain during acute hypernatremia.
Authors: Cserr H F , DePasquale M , Nicholson C , Patlak C S , Pettigrew K D , Rice M E
Published: December 2014

1. Regulation of brain extracellular and intracellular water content, regarded as volume, and electrolytes in response to 90 min of hypernatremia has been studied in the cerebral cortex of rats under urethane anaesthetic. 2. Total tissue electrolytes and water were partitioned between extracellular and intracellular compartments based on measurements made in two series of experiments. In one, tissue samples were collected and analysed for total water, Na+, K+ and Cl‐. In the other, tissue extracellular volume fraction, [Na+] and [K+] were measured in situ using ion‐selective microelectrodes. 3. Osmotically induced water loss from cerebral cortex was less than that predicted for ideal osmotic behaviour, revealing a degree of volume regulation, and this regulation was associated with net tissue uptake of Na+, Cl‐ and K+. 4. Total water content was 3.77 g H2O (g dry weight)‐1 in control cortex and this decreased by 7% after 30 min of hypernatremia and then remained relatively stable at this value. Control extracellular water content, based on an extracellular volume fraction of 0.18, was 0.88 g H2O (g dry weight)‐1. Control intracellular water content, estimated as the difference between total and extracellular water contents, was 2.89 g H2O (g dry weight)‐1. After 30 min of hypernatremia, extracellular water content decreased by an average of 27% but intracellular water did not change. This indicates selective regulation of cell volume. By 90 min the extracellular water content had decreased by 47% and the loss in extracellular water content appeared to be accompanied by a roughly equivalent increase in intracellular water content. The intracellular volume increase, however, was not statistically significant. The tortuosity of the extracellular space averaged 1.57 and increased to 1.65 during the hypernatremia. 5. Brain extracellular fluid and plasma [Na+] were roughly equal in control tissue. Both increased by 30 mu equiv (g H2O)‐1 as a result of the hypernatremia, although extracellular [Na+] lagged behind the plasma value during much of the first 60 min of hypernatremia. Extracellular [K+] was homeostatically regulated at 3 mu equiv (g H2O)‐1 independent of changes in plasma electrolytes. 6. Estimates of extracellular and intracellular ion content (mu equiv (g dry weight)‐1) indicate that extracellular Na+, Cl‐ and K+ content decreased during hypernatremia, by 32, 21 and 42% respectively, whereas intracellular ion content increased by 100, 169 and 5% respectively. 7. It is concluded that during acute hypernatremia the extracellular space decreases in volume through the loss of water and electrolytes while the intracellular compartment maintains its water content and gains electrolytes.(ABSTRACT TRUNCATED AT 400 WORDS)
ACTH release induced in rats by noradrenaline is mediated by prostaglandin E2.
Authors: Watanabe T , Morimoto A , Morimoto K , Nakamori T , Murakami N
Published: December 2014

1. We investigated the involvement of prostaglandin E2 in the development of the adrenocorticotrophic hormone (ACTH) response induced by noradrenaline (NA) in rats. 2. Intravenous (i.v.) injection of NA produced dose‐dependent increases in the plasma concentration of ACTH and prostaglandin E2. However, pre‐treatment with systemic administration of indomethacin, an inhibitor of prostaglandin synthesis, significantly suppressed this increase in plasma ACTH. 3. The i.v. injection of prostaglandin E2 significantly increased the plasma concentration of ACTH in a dose‐dependent manner. In contrast, ACTH responses induced by the i.v. injection of prostaglandin E2 were significantly suppressed by systemic pre‐treatment with anti‐corticotrophin‐releasing factor antibody (anti‐CRF), although the plasma level of ACTH still increased in comparison to the basal level. 4. These results suggest that NA‐stimulated prostaglandin release is involved in the ACTH response induced by NA. In addition, it is likely that CRF may be responsible for a portion of the ACTH response induced by i.v. injection of prostaglandin E2.
Sodium channel inactivation from resting states in guinea‐pig ventricular myocytes.
Authors: Lawrence J H , Yue D T , Rose W C , Marban E
Published: December 2014

1. Unitary Na+ channel currents were recorded from isolated guinea‐pig ventricular myocytes using the cell‐attached patch‐clamp technique with high [Na+] in the pipette to enhance the signal‐to‐noise ratio. 2. The probability that the channel enters the inactivated state (I) directly from resting states (C) was investigated over a wide range of membrane potentials. 3. At membrane potentials of ‐60 mV or more positive, Markov chain theory was used to estimate the probability of C‐‐‐‐I from histograms of the number of channel openings per depolarizing period. Holding potentials at least as negative as ‐136 were required to ensure that all channels resided in C prior to depolarization. 4. At membrane potentials negative to ‐60 mV, a two‐pulse protocol was employed to determine the probability of C‐‐‐‐I from the fraction of blank sweeps during the pre‐pulse with correction for missed events. 5. The probability of C‐‐‐‐I was found to be steeply voltage dependent at negative potentials, falling from 0.87 +/‐ 0.03 (mean +/‐ S.D.) at ‐91 mV to 0.42 +/‐ 0.01 at ‐76 mV. At potentials positive to ‐60 mV, this probability was less steeply voltage dependent and decayed to near zero at 0 mV. 6. Under physiological conditions, C‐‐‐‐I transitions may produce appreciable Na+ channel inactivation at diastolic potentials. At potentials above the action potential threshold, inactivation is much more likely to occur from the open state.
Role of the carotid bodies in the respiratory compensation for the metabolic acidosis of exercise in humans.
Authors: Rausch S M , Whipp B J , Wasserman K , Huszczuk A
Published: December 2014

1. In response to an acute exercise‐induced metabolic acidosis, the fall of arterial pH is constrained by the magnitude of the compensatory hyperventilation. To determine the role of the carotid bodies in this regulatory process, subjects performed prolonged (24 min) square‐wave cycle ergometry from a background of unloaded cycling at inspired oxygen fractions (FI,O2) of 0.12 O2 (high carotid body gain), 0.21 O2 (normal carotid body gain) and 0.80 O2 (low carotid body gain). The work rates were selected to provide the same exercise intensity, despite the different inspirates; i.e. resulting in a constant increase in arterial blood [lactate] (delta [L‐] approximately 4 mequiv l‐1. 2. Ventilatory and pulmonary gas exchange variables were computed breath‐by‐breath and arterial blood was sampled at intervals throughout the tests and analysed subsequently for [lactate], [pyruvate], arterial partial pressures of oxygen and carbon dioxide (PO2, PCO2), pH, [bicarbonate] and [potassium]. 3. Hypoxia markedly reduced, and hyperoxia magnified, the transient decrease in arterial pH following exercise onset. However, there was a slow acid‐base compensatory component, even when carotid chemosensitivity was suppressed by hyperoxia. We therefore conclude that, in humans, carotid body chemosensitivity plays a dominant role in constraining variations of arterial pH in response to the acute metabolic acidosis of heavy exercise, but that secondary‐presumably central chemosensory‐mechanisms subserve a slower compensatory role.
Differential blockage of charge movement components in frog cut twitch fibres by nifedipine.
Authors: Chen W , Hui C S
Published: December 2014

1. The effect of nifedipine on charge movement was studied in cut twitch fibres of Rana temporaria with a double Vaseline‐gap voltage‐clamp technique. The steady‐state charge‐voltage (Q‐V) plot, in the absence or presence of nifedipine, was separated into Q beta and Q gamma components by fitting with a sum of two Boltzmann distribution functions. 2. When a fibre was held at ‐90 mV, low concentrations (around 20 nM) of nifedipine suppressed a large fraction of Q beta than Q gamma. Higher concentrations of nifedipine suppressed Q gamma more effectively than Q beta, but even 2 microM‐nifedipine did not suppress Q beta and Q gamma completely. Ten micromolar was required for complete suppression of Q gamma. Nifedipine thus suppressed Q beta and Q gamma with different dose dependencies. 3. When the holding potential was changed to ‐70 mV, some Q beta and Q gamma were inactivated. Low concentrations (around 20 nM) of nifedipine still suppressed a larger fraction of the mobile Q beta than the mobile Q gamma. Higher concentrations of nifedipine also suppressed Q gamma more effectively than Q beta, but 2 microM‐nifedipine was sufficient to suppress Q gamma completely. Hence, at this slightly depolarized holding potential, nifedipine also suppressed Q beta and Q gamma with different dose dependencies. 4. A portion of Q beta appeared to be resistant to the action of nifedipine. At ‐70 mV, the blockage of the nifedipine‐sensitive portion of Q beta appeared to saturate at 2 microM of the drug. At ‐90 mV, the nifedipine‐resistant portion of Q beta was more difficult to identify, because the blockage of the nifedipine‐sensitive portion of Q beta did not saturate at 2 microM. 5. Based on double‐reciprocal plots for the dose‐response relationships, the half‐blocking concentration of nifedipine for Q beta was found to be 14‐19 nM at ‐90 mV and less than 13 nM at ‐70 mV, whereas that for Q gamma was approximately 1.6 microM at ‐90 mV and 120 nM at ‐70 mV. Thus, nifedipine suppressed Q gamma in a voltage‐dependent manner, but its suppression of Q beta was much less voltage dependent. 6. It was demonstrated that the enhancement in the blockage of charge movement by maintained depolarization could not be achieved by depolarizing pulses lasting up to hundreds of milliseconds. 7. The difference in the half‐blocking concentrations of nifedipine for Q beta and Q gamma implies that Q beta and Q gamma cannot be tightly coupled.
Depolarization of Ib afferent axons in the cat spinal cord during homonymous muscle contraction.
Authors: Lafleur J , Zytnicki D , Horcholle‐Bossavit G , Jami L
Published: December 2014

1. Intra‐axonal records from the intraspinal course of Ib and Ia afferent fibres innervating the gastrocnemius medialis muscle were obtained in chloralose or Nembutal‐anaesthetized cats during submaximal contractions of the muscle. 2. Afferent fibres in continuity with their muscle of origin were functionally identified by their responses to muscle stretch or contraction. 3. In six out of eight Ib afferents, primary depolarizations (PADs) were recorded during contraction. They were independent of the presence of orthodromic impulses fired by tendon organs. 4. These observations support the assumption that the reduction of Ib autogenetic inhibition in homonymous and synergic motoneurones during GM contractions is due to presynaptic inhibition of transmission in Ib pathways.
The source of calcium for muscarinic‐mediated catecholamine release from cat adrenals.
Authors: Abad F , Garrido B , López M G , García A G
Published: December 2014

1. In view of conflicting reports on the source of Ca2+ needed to trigger the secretory response to muscarinic stimulation of chromaffin cells, we have reinvestigated this problem in the cat adrenal gland perfused with oxygenated Krebs solution at 37 degrees C. Above a basal rate of secretion of 60 ng/30 s of total catecholamines, 5 s pulses of 100 microM‐methacholine evoked 10‐fold increases of secretion. This response was entirely mediated by muscarinic receptors, since it was blocked by submicromolar concentrations of atropine but not by d‐tubocurarine. 2. Delayed application of methacholine pulses after Ca2+ removal from the Krebs solution led to a progressive decline of the secretory response with a t1/2 of 15 s. Secretion was blocked by 85% after a 60 s period of Ca2+ deprivation; extension of the external Ca2+ (Ca2+o) wash‐out period up to 5 min did not further reduce the secretory response. 3. When EGTA (1 mM) was present in the 0 Ca2+ solution, the rate of decline of methacholine responses, as a function of the time of exposure to 1 mM‐EGTA, was similar to that obtained with 0 Ca2+. Again, about 15‐20% of the secretory response was resistant even to prolonged periods of washing out with the 0 Ca(2+)‐EGTA solution. 4. The Ca2+ ionophore ionomycin (1 microM) first decreased and then accelerated the rate of decline of methacholine responses upon Ca2+o wash‐out. Particularly relevant is the complete blockade of secretion when the Ca2+o wash‐out is performed in the presence of this ionophore. This suggests the existence of a small intracellular functional Ca2+ store sensitive to ionomycin. 5. After abolition of the secretory response through 60 s periods of wash‐out with a 0 Ca(2+)‐EGTA‐ionomycin solution, followed by delayed 5 s methacholine pulses after Ca2+o reintroduction, the glands instantly recovered their normal muscarinic‐mediated secretory response. This suggests that upon muscarinic stimulation, Ca2+ required by the secretory machinery to trigger such response immediately comes from extracellular sources. How Ca2+o gains the cell interior so fast upon muscarinic stimulation is unknown; we have previously suggested that the muscarinic receptor in the cat chromaffin cell could be coupled to an ionophore channel which might be chemically activated by muscarinic agonists. 6. Secretory responses to 5 s pulses with 35 or 100 mM‐K+ declined faster (t1/2 of 3 and 6 s, respectively) upon Ca2+o wash‐out than those of methacholine.(ABSTRACT TRUNCATED AT 400 WORDS)
In vitro studies of prolonged synaptic depression in the neonatal rat spinal cord.
Authors: Lev‐Tov A , Pinco M
Published: December 2014

1. Synaptic transmission between dorsal root afferents and alpha‐motoneurones was studied in the in vitro hemisected spinal cord preparation isolated from neonatal rats. 2. Repetitive stimulation of the dorsal roots depressed the monosynaptic reflex recorded from the homologous ventral roots. The depression developed within the first five to six pulses in a stimulus train and stabilized at a plateau‐like level for many seconds of stimulation. 3. The magnitude of the reflex depression depended on the stimulation interval and was capable of reducing the reflex to 17% of its undepressed control during 5 Hz stimulus trains. Complete recovery from depression was obtained at stimulation intervals greater than or equal to 30 s. 4. Monosynaptic excitatory postsynaptic potentials (EPSPs) were recorded intracellularly after reduction of the activity in polysynaptic pathways by addition of mephenesin to the bathing media. These EPSPs exhibited a prolonged, frequency‐dependent synaptic depression. The depression reduced the amplitude of the EPSP to 25% of the undepressed control during 5 Hz stimulus trains, and was alleviated completely at stimulus interval greater than or equal to 60 s. 5. The prolonged EPSP depression was not altered by blockade of glycinergic and type‐A gamma‐aminobutyric acid (GABAA‐ergic) receptors underlying postsynaptic inhibition in the spinal cord. Injection of current steps to motoneurones before and during the prolonged depression revealed similar values of the membrane time constant and input resistance. These excluded changes in the passive properties of the motoneurone membrane as an explanation for the observed synaptic depression. 6. Extracellular recordings of terminal potentials and their accompanying synaptic fields from motor nuclei in the ventrolateral cord revealed that the frequency‐dependent depression in the synaptic fields was not preceded by any detectable changes in the amplitude or the shape of the terminal potential, suggesting that the depression cannot be attributed to impairment of action potential invasion to the afferent terminals. 7. Reduction of the basic level of transmitter release in the spinal cord by increasing the Mg2+/Ca2+ ratio of the bathing solution or by application of 2 microM of L(‐)baclofen markedly diminished the synaptic potential depression at all the stimulation intervals tested in this study. Recovery from depression was evident for stimulation intervals greater than or equal to 5 s. Under these conditions, short tetanic trains (5 pulses at 25 Hz) revealed a substantial facilitation and potentiation of the EPSPs. 8. We suggest that prolonged depression of synaptic potentials in the neonatal rat reflects decreased transmitter output from the activated afferent terminals.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium influx and calcium current in single synaptic terminals of goldfish retinal bipolar neurons.
Authors: Heidelberger R , Matthews G
Published: December 2014

1. The calcium influx pathway in large synaptic terminals of acutely isolated bipolar neurons from goldfish retina was characterized using Fura‐2 measurements of intracellular calcium and patch‐clamp recordings of whole‐cell calcium current. 2. Depolarization of bipolar cells with high [K+]o resulted in a sustained, reversible increase in [Ca2+]i in both synaptic terminals and somata. Removal of external calcium abolished the response, as did the addition of 200 microM‐cadmium to the bathing solution, indicating that the rise in [Ca2+]i was due to entry of external calcium. Dihydropyridine blockers of voltage‐gated Ca2+ channels also blocked the influx, and the Ca2+ channel agonist Bay K 8644 potentiated influx, implicating voltage‐activated, dihydropyridine‐sensitive channels in the influx pathway. 3. Under voltage clamp, depolarization from a holding potential of ‐60 mV evoked a slowly inactivating inward current that began to activate at ‐50 to ‐40 mV and reached a maximal amplitude between ‐20 and ‐15 mV. This current was identified as a calcium current because it decreased when the extracellular calcium concentration was lowered, increased when barium was the charge carrier, and was blocked by 200 microM‐external cadmium. The current was substantially blocked by 1 microM‐nitrendipine and potentiated by 0.1 microM‐Bay K 8644, as expected for L‐type Ca2+ channels; it was unaffected by omega‐conotoxin. No evidence for transient or rapidly inactivating Ca2+ current was found. 4. At a given level of potassium depolarization, both the amplitude and the speed of increase in [Ca2+]i were greater in synaptic terminals than in somata. For instance, depolarization by 32.6 mM‐potassium caused an increase in intracellular calcium of 400 +/‐ 23 nM in terminals and 180 +/‐ 20 nM in somata (mean +/‐ S.E.M., n = 73 terminals, n = 30 somata), with maximal rates of change of 40 +/‐ 3 and 12 +/‐ 2 nM/s, respectively. 5. The contribution of terminal and somatic currents to the total whole‐cell Ca2+ current was determined under voltage clamp by local application of calcium or of blocking agents. While there was no qualitative difference between currents in terminals and somata, synaptic terminals accounted for 64 +/‐ 3% (mean +/‐ S.E.M., n = 12) of the total whole‐cell calcium current, and somata accounted for 39 +/‐ 2%. Thus, the density of Ca2+ current was higher in the terminal, accounting for the greater magnitude and speed of Ca2+ influx observed in terminals in Fura‐2 experiments.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of GABAA and GABAB receptors in presynaptic inhibition of Ia EPSPs in cat spinal motoneurones.
Authors: Stuart G J , Redman S J
Published: December 2014

1. The role of GABAA and GABAB receptors in presynaptic inhibition was studied by examining the effect of local application of antagonists by ionophoresis during intracellular recording of presynaptic inhibition of compound and unitary group Ia afferent excitatory postsynaptic potentials (EPSPs) in gastrocnemius motoneurones. 2. Ionophoresis of the GABAA antagonist bicuculline methochloride (BMC) was found to block presynaptic inhibition of both compound and unitary EPSPs by up to 85%. BMC also substantially reduced, and occasionally abolished, the late part of the inhibitory postsynaptic potential (IPSP) evoked in motoneurones by the conditioning stimulation. The early part of this IPSP was found to be sensitive to ionophoresis of strychnine hydrochloride. 3. Ionophoresis of 2‐OH‐saclofen caused a reduction in presynaptic inhibition of compound EPSPs by 5‐25% but had no effect on the IPSP evoked in motoneurones by the conditioning stimulation. 4. Ionophoresis of the GABAB antagonist (‐)‐baclofen reduced the amplitude of unconditioned EPSPs; however it had little effect on presynaptic inhibition. 5. It was concluded that at the Ia afferent‐motoneurone synapse presynaptic inhibition is mediated primarily through the activation of GABAA receptors. The activation of GABAB receptors appears to play only a minor role in presynaptic inhibition at this synapse. This contrasts with the relative ease with which (‐)‐baclofen can reduce transmitter release from Ia afferent terminals and suggests that the receptors activated by (‐)‐baclofen are predominantly extrasynaptic.
Ionic currents of outer hair cells isolated from the guinea‐pig cochlea.
Authors: Housley G D , Ashmore J F
Published: December 2014

1. Whole‐cell currents were measured in outer hair cells isolated from each turn of the organ of Corti of the guinea‐pig. 2. The slope input conductances at ‐70 mV of the cells ranged from 3.6 to 51 nS depending on the length of the cell. Shorter cells from the basal turns of the cochlea had the highest values. The membrane time constant of the cells varied from 3 to 0.2 ms from the apex to the base. 3. Irrespective of the position of the cells along the cochlea, three distinct currents were found. Each type of current was found in approximately the same proportion in all cells. 4. An outward K+ current was present which activated at potentials more positive than ‐35 mV. The current was sensitive to tetraethylammonium (30 mM), quinidine (100 microM) and nifedipine (50 microM). It could be removed by replacing external Ca2+ with Ba2+ or Mg2+. The current was also removed by substituting Nai+ or Csi+ for Ki+ pipette solution. This outwardly rectifying current appears similar to the calcium‐activated K+ current described in other hair cells. 5. The main current present at membrane potentials from ‐90 mV to ‐50 mV was a second voltage‐activated K+ current. It was 50% activated at ‐80 mV, and relaxed with a time constant of 20‐40 ms on hyperpolarization to ‐120 mV. Near rest the kinetics were essentially time‐dependent , but depended upon the external K+ concentration. The current was blocked by 5 mM external Cs+. 6. This current was highly selective for K+. Measured from reversal of the tail currents, the permeability ratio PK:PNa was approximately 30:1. Depolarization of the cell, presumed to lead to an elevation of intracellular calcium, produced a prolonged activation of the current. 7. A third current found in the cells was a cation current. By external ion replacement, the selectivity sequence was determined to be Ca2+ greater than Na+ approximately equal to K+ greater than choline+ greater than NMDG+ (respective permeabilities relative to Na: 2.9, 1.0, 0.99, 0.63 and 0.37). This current was reduced by external Ba2+ (3 mM) and by nifedipine (50 microM). The activation of this current appeared to depend upon raised levels of Cai2+. 8. These currents account for reported in vivo properties of cochlear outer hair cells as cells permeable to potassium at large negative resting potentials. The consequences for sound detection in the cochlea are briefly discussed.
The role of nociceptors of cutaneous veins in the mediation of cold pain in man.
Authors: Klement W , Arndt J O
Published: December 2014

1. To test the hypothesis that nociceptors of cutaneous veins mediate cold pain, we studied in man the time course of pain intensity and skin sensibility in relation to both intracutaneous and vein wall temperature during cooling of the dorsum of the hand by ice water before and after perivenous and intravenous nerve block. 2. Upon exposure to cold, intracutaneous temperatures fell exponentially (half‐life/45‐75s) within 10 min to a median of 4 degrees C (range 2‐9 degrees C) and returned to baseline with a similar time course during rewarming (half‐life/40‐85 s). 3. Skin sensitivity to pin prick disappeared and returned at almost the same intracutaneous temperatures (16‐26 degrees C). Pain, however, occurred and eve increased when the skin was already numb. 4. Pain occurred during cooling and disappeared during rewarming at vein wall temperatures between 23 and 28 degrees C and its intensity increased to a maximum of 72‐100% of visual analogue scale as vein wall temperature decreased to a minimum of 9 degrees C (range 7‐10.5 degrees C). 5. the pain intensity‐vein wall temperature relations derived from skin cooling with threshold temperature changes between ‐5.5 and ‐9 degrees C and slopes between 2.2 and 3.3 were congruent to those derived from intravenous cooling in a previous study to ours. 6. Perivenous and intravenous nerve block, which did not alter the sensitivity of skin and periosteum, relieved cold pain markedly (perivenous block) or completely (intravenous block). 7. These observations are consistent with the hypothesis that nociceptors of cutaneous veins mediate cold pain in humans.
Fast and slow components of unitary EPSCs on stellate cells elicited by focal stimulation in slices of rat visual cortex.
Authors: Stern P , Edwards F A , Sakmann B
Published: December 2014

1. Voltage and current recordings were made from visually identified non‐pyramidal neurones in slices of layer IV of rat primary visual cortex using the whole‐cell configuration of the patch clamp technique. These neurones are characterized by a high input resistance (0.5‐2 G omega) and a non‐adaptive behaviour of action potential frequency following depolarizing current injection, which suggests that they are stellate cells. 2. Excitatory postsynaptic currents (EPSCs) were recorded from these neurones during focal stimulation of neighbouring cells by a second patch pipette, the tip of which was placed on the soma of the stimulated cell. The response amplitude as a function of stimulus strength showed a sharp increase at a critical stimulus strength suggesting that stimulus‐evoked currents represent unitary EPSCs. 3. In most cases the latencies of stimulus‐evoked EPSCs were unimodally distributed with means in the range of 2.1‐3.6 ms. In some experiments two peaks were seen in the distribution of latencies. The EPSC rise times, measured as the time from 20 to 80% peak amplitude, fell into a distribution ranging from 0.1 to 0.8 ms with a peak at 0.2 ms. The EPSC decay time course at ‐70 mV membrane potential was fitted by a single exponential with a time constant of 2.39 +/‐ 0.99 ms (mean +/‐ S.D.). The rise and decay times were independent of EPSC peak amplitudes. 4. The peak amplitude of successive unitary EPSCs, elicited by a constant stimulus, fluctuated at random. At a holding potential of ‐70 mV the peak amplitudes varied between 5 and 90 pA. In two out of ten cells the histogram of peak amplitudes could be well fitted by the sum of several equidistant Gaussians with a peak distance of around 10 pA. This suggests that the quantal conductance change underlying the peak current fluctuations is of the order of 100 pS. 5. At membrane potentials more positive than ‐70 mV the decay of stimulus‐evoked EPSCs showed two components with very different time courses. In standard extracellular solution the current‐voltage (I‐V) relation for the fast component was almost linear whereas the slow component showed a J‐shaped I‐V relation with a region of negative slope conductance between ‐30 and ‐70 mV.(ABSTRACT TRUNCATED AT 400 WORDS)