bluuebunny/crossref_metadata_2025 huggingface dataset:
Force development and relaxation in single motor units of adult cats during a standard fatigue test.
Authors: Gordon D A , Enoka R M , Karst G M , Stuart D G
Published: December 2014

1. The purpose of this study was to investigate tetanic force development and relaxation in single motor units that were subjected to a standard fatigue test. 2. Motor units of tibialis posterior, a hindlimb muscle in the adult cat, were assigned to four categories (i.e. types S, FR, FI, FF) using conventional criteria. 3. Based on the first tetanus of the fatigue test, type S units took significantly longer to develop force and to relax than the fast‐twitch units. Within the fast‐twitch subpopulations, type FR and FI units were significantly slower to develop force and to relax than were type FF units, but there were no significant differences between type FR and FI units. 4. After 120 s of the fatigue test, the rates of force development were faster than initial values in type S and FR units, but were largely unchanged for the type FI and FF units. Most relaxation parameters were unaffected by stimulation in type S and FR units, but all parameters became significantly slower in type FI and FF units. 5. The average time courses of force development and relaxation showed that during 240 s of the fatigue test, type S units exhibited either a progressive increase in a parameter or no change at all. In contrast, fast‐twitch units displayed profiles that included initial increases in a force development or relaxation parameter followed by variable amounts of decline that corresponded to fatigability. 6. It is concluded that repetitive activation affects the development and relaxation of tetanic force in all motor‐unit types. Average changes in these parameters tended to parallel the conventional classification of motor units into four categories.
Responses to changes in filling and contractility of indices of human left ventricular mechanical performance.
Authors: Drake‐Holland A J , Mills C J , Noble M I , Pugh S
Published: December 2014

1. Beat‐by‐beat indices of contractility for assessment of inotropic effects in a given subject were studied using pacing with beta‐adrenergic blockade, in eight patients undergoing routine left heart catheterization. A catheter‐tip manometer was sited in the left ventricle and an electromagnetic velocity transducer was mounted further back on the same catheter so that it was sited in the ascending aorta. 2. The maximum rate of rise of left ventricular pressure (dPLV/dtmax), and of aortic velocity (maximum acceleration, MA) and stroke volume (SV) were all obtained with this catheter. Filling effects were assessed by head‐up to head‐down tilt, inotropic effects by paced post‐extrasystolic potentiation. 3. Tilt produced a mean increase in left ventricular end‐diastolic pressure (PLVED) of 8.1 mmHg (P less than 0.05), dPLV/dtmax decreased 4.3% (n.s.), peak velocity (PV) increased 23% (P less than 0.05), MA increased 5.4% (n.s.), and SV increased 17.5% (P less than 0.05). Post‐extrasystolic potentiation produced a mean decrease in PLVED of 2.8 mmHg (n.s.), dPLV/dtmax increased 35% (P less than 0.05), PV increased 14% (P less than 0.05), MA increased 55% (P less than 0.05), and SV increased 8.7% (n.s.). 4. There was no difference in response between patients with normal and patients with impaired left ventricular ejection fraction. 5. It is concluded that increased left ventricular filling increases stroke volume greatly (Starling effect) but does not affect dPLV/dtmax, which (together with MA) nevertheless responds markedly to increased contractility. dPLV/dtmax appears to be a volume‐insensitive index of contractility in the intact human, whether ejection fraction is normal or impaired.
Transport of leucine, isoleucine and valine by luminal membrane vesicles from rabbit proximal tubule.
Authors: Jørgensen K E , Kragh‐Hansen U , Sheikh M I
Published: December 2014

1. Transport of L‐ and D‐isomers of leucine, isoleucine and valine by luminal membrane vesicles prepared from either the convoluted part (pars convoluta) or the straight part (pars recta) of rabbit proximal tubule was studied by a rapid filtration technique and by a spectrophotometric method using a potential‐sensitive carbocyanine dye. 2. Both types of renal membrane vesicle take up the amino acids in a Na(+)‐dependent, H(+)‐independent and electrogenic manner. The L‐isomers are transported with higher affinities than their corresponding D‐forms, of which only D‐leucine is taken up to a significant extent. 3. Membrane vesicles prepared from pars convoluta take up the L‐amino acids by a single and common system. Filtration studies showed that the Km values for L‐leucine and L‐valine transport are, on average, 0.23 and 0.83 mM, respectively. The values of KA (the concentration of amino acid producing a half‐maximal optical response) are comparable to those of Km, namely 0.18 mM for L‐leucine and 0.60 mM for L‐valine. KA for L‐isoleucine transport was found to be 0.19 mM. D‐Leucine is taken up by the same system but with a much lower affinity (KA = 7.2 mM). 4. Membrane vesicles prepared from pars recta possess two, and probably common, transport systems for the L‐isomers of the amino acids. The average Michaelis‐Menten constants were as follows: L‐leucine, K1m = 0.17 mM, K2m = 6.5 mM; L‐valine, K1m = 0.19 mM, K2m = 11.5 mM. The KA values were: L‐leucine, K1A = 0.12 mM, K2A = 7.4 mM; L‐valine, K1A = 0.18 mM, K2A = 10.0 mM; L‐isoleucine, K1A = 0.17 mM, K2A = 9.0 mM. D‐Leucine is taken up by a low‐affinity system only (KA = 6.5 mM), which seems to be the same as the low‐affinity system transporting the L‐forms of the amino acids.
Effects of immobilization on contractile properties, recruitment and firing rates of human motor units.
Authors: Duchateau J , Hainaut K
Published: December 2014

1. The contractile properties, recruitment and firing rates of motor units from the human adductor pollicis and the first dorsal interosseous were studied during voluntary isometric contractions after 6‐8 weeks' immobilization of the corresponding limbs. 2. In both muscles, motor units of different force thresholds showed a proportionally identical twitch tension decrease and slowing of their time course after immobilization. 3. When expressed as a percentage of the maximal voluntary contraction, more high‐threshold motor units were recorded in disused muscles than in control muscles, but the order of recruitment was maintained. 4. The motor unit firing rate at recruitment was identical in control and disused muscles, but the maximal firing rate decreased in all motor units after immobilization. This decrease of the maximal firing rate was greater in motor units of lower threshold than in those of higher threshold. 5. The results further document motoneuronal plasticity in human muscles of different fibre type composition.
Nicotinic acetylcholine receptors in porcine hypophyseal intermediate lobe cells.
Authors: Zhang Z W , Feltz P
Published: December 2014

1. Acetylcholine (ACh) was found to depolarize isolated porcine intermediate lobe cells maintained in primary cells culture. We investigated the ACh‐induced responses in both whole‐cell and cell‐attached configurations of the patch‐clamp technique. 2. From noise analysis of ACh‐evoked whole‐cell currents, we estimated an elementary conductance of 20 pS and a channel open duration of about 1.7 ms at ‐60 mV. From single‐channel recordings, we obtained a slope conductance of 26 pS and a mean open time of 1.8 ms at membrane potentials between ‐60 and ‐80 mV. 3. ACh‐evoked responses were blocked by d‐tubocurarine (d‐TC), hexamethonium and mecamylamine, but were insensitive to alpha‐bungarotoxin. These characteristics define a neuronal type of nicotinic receptors. 4. The whole‐cell current induced by ACh showed a strong inward rectification with no outward current being obtained. This phenomenon was observed when the intracellular ion is either sodium or caesium, and even when Ca2+ and Mg2+ were totally removed from the intracellular medium. 5. ACh‐gated channels in intermediate lobe cells were cation selective and were permeable to Na+ and Cs+. In Ca2(+)‐free extracellular solution, single‐channel conductances were much larger (46 pS) than in the presence of 2 mM‐Ca2+ (26 pS). 6. The possibility of an excitatory cholinergic control of intermediate lobe cells is discussed.
Modulation of potassium channels in human T lymphocytes: effects of temperature.
Authors: Pahapill P A , Schlichter L C
Published: December 2014

1. The predominant channels found in lymphocytes with patch‐clamp whole‐cell recordings are voltage‐gated K+ channels. Several lines of evidence suggest that these channels are involved in lymphocyte function. Most lymphocyte functions are temperature sensitive and have not been correlated with electrophysiology at different temperatures. We have examined the effect of temperature on the voltage‐dependent K+ channel in normal human T lymphocytes. Both macroscopic current and single‐channel events were studied with whole‐cell recordings at temperatures from 5 to 42 degrees C. 2. Peak conductance, activation rate, inactivation rate and rate of recovery from inactivation all increased progressively as the temperature increased. The effect of temperature on channel opening processes was greater at low temperatures. In contrast, the inactivation process was most sensitive to temperature changes above room temperature. Arrhenius plots of conductance and kinetic parameters were curvilinear with no obvious break‐points. 3. The increase in whole‐cell conductance at 37 degrees C was due to both an increase in the single‐channel conductance and in the probability that each channel is open at any time. 4. K+ currents were fitted by Hodgkin‐Huxley equations with n4j kinetics providing the best description of the currents at all temperatures tested. 5. Steady‐state activation‐ and inactivation‐voltage curves shifted in opposite directions with warming, resulting in a greater area of overlap of the curves ('window' current). The increase in resting K+ channel activity predicted by a greater window current was confirmed with single‐channel measurements. 6. The present study has shown that the behaviour of K+ channels in human T lymphocytes is temperature dependent.
Acidosis and blockade of orthodromic responses caused by anoxia in rat hippocampal slices at different temperatures.
Authors: Krnjević K , Walz W
Published: December 2014

1. Interstitial pH (pHo) and field responses (to stratum radiatum stimulation) were recorded simultaneously with double‐barrelled microelectrodes in the CA1 region of hippocampal slices from Sprague‐Dawley rats. 2. Both the relative acidity and amplitude of field responses increased with depth, reaching a maximum near the centre of the slice. When the temperature was raised from 22 to 37 degrees C, this pHo gradient was greater than 2 times steeper, but the field responses were much diminished. 3. Standard anoxic tests (substituting 95% N2 + 5% CO2 for 95% O2 + 5% CO2, for 2 min) tended to reduce pHo and population spikes, but these effects were highly temperature sensitive: at approximately 22 degrees C the blocking rate was only 12.3 +/‐ 4.6% and delta pHo ‐0.018 +/‐ 0.0157 units, both per minute; corresponding changes at 34‐35 degrees C were 67.6 +/‐ 11.9% and ‐0.065 +/‐ 0.0046 units per minute. Highly significant linear correlations between rates of block and delta pHo gave a mean slope of 90.4 +/‐ 17.6% per 0.1 unit of acid change. 4. Anoxia caused similar temperature‐dependent increases in acidity in stratum pyramidale and radiatum, but in the latter field responses (EPSPs) were much less depressed after 2 min of anoxia. 5. When slices were superfused with acid medium (low [HCO3‐]), much greater reductions in pHo were needed to depress responses, giving a mean slope of 17.7% per 0.1 pH unit. 6. In glucose‐free medium, there was a slow alkaline shift in pHo (0.13 +/‐ 0.036 units); population spikes and the acid transients evoked by anoxia disappeared. 7. It was concluded that acidosis cannot be the immediate cause of the similar depressions of postsynaptic excitability seen during anoxia and hypoglycaemia. 8. In further tests, DL‐p‐hydroxyphenyl‐lactic acid, a blocker of lactate transport, failed to diminish acid transients evoked by anoxia, indicating that these are not mediated principally by lactate transport.
Local oxygen supply and blood flow regulation in contracting muscle in dogs and rabbits.
Authors: Harrison D K , Birkenhake S , Knauf S K , Kessler M
Published: December 2014

1. Multiwire surface electrodes were used to measure local hydrogen clearance curves and tissues PO2 in the sartorius muscle in dogs under resting conditions and during stimulation of the muscle at 1, 2, 4, 8 and 20 Hz via the femoral nerve. Tissue oxygen supply was assessed by means of PO2 histograms; evaluation of the initial slopes of the hydrogen clearance curves enabled the measurement of capillary blood flow. 2. In a further model, the analysis of hydrogen clearance curves measured in the femoral vein using intravascular needle electrodes in rabbits enabled the distribution of blood flow to be evaluated both under resting conditions and during direct 2 Hz stimulation of the vastus medialis muscle. 3. Increased oxygen consumption, induced by stimulation, caused increases in capillary flow which were not necessarily accompanied by augmentation of femoral artery flow. 4. PO2 histograms provided no evidence of cellular anoxia even at the maximum level of oxygen consumption. 5. A two‐compartment distribution of flow was measured under resting conditions, whereas only one compartment could be resolved during 2 Hz stimulation of the vastus medialis muscle in the rabbit experiments. A clear redistribution of flow was observed in the absence of any increase in total flow. 6. A model for oxygen‐dependent regulation of capillary blood flow involving high‐flow and normal‐flow compartments is proposed.
Muscarine reduces inwardly rectifying potassium conductance in rat nucleus accumbens neurones.
Authors: Uchimura N , North R A
Published: December 2014

1. Intracellular recordings were made from neurones in the nucleus accumbens in slices from the rat brain maintained in vitro. 2. Muscarine (1‐100 microM) depolarized 101 of 107 neurones; this was associated with an increase in the input resistance. The potential change reversed polarity with conditioning hyperpolarization and the reversal potential was linearly related to the logarithm of the extracellular potassium concentration. 3. The depolarization caused by muscarine was not changed by tetrodotoxin (1 microM) or by a solution that contained lower levels of calcium (0.24 instead of 2.4 mM), higher levels of magnesium (5 instead of 1.2 mM) and cobalt (2 mM). 4. Muscarine caused an inward current and a decrease in slope conductance when applied to neurones voltage clamped near their resting potential (‐82 mV). The current caused by muscarine reversed polarity at the potassium equilibrium potential. The current‐voltage relation of the neurones between ‐60 and ‐120 mV was well fitted by assuming a voltage‐independent potassium conductance and an inward rectifier potassium conductance; muscarine reduced predominantly the inward rectifier conductance. 5. Phorbol‐12,13‐diacetate (3 microM) and 5‐hydroxytryptamine mimicked the action of muscarine. The inward currents caused by muscarine or 5‐hydroxytryptamine were occluded by the inward current evoked by the phorbol ester. 6. The depolarization caused by muscarine was competitively antagonized by pirenzepine; the dissociation constant of 11 nM suggested involvement of the M1 receptor. 7. It is concluded that muscarine acts at M1 receptors to reduce the membrane potassium conductance and that activation of protein kinase C may be an intermediate step.
Nerve‐mediated contractions of sheep mesenteric lymph node capsules.
Authors: Thornbury K D , McHale N G , Allen J M , Hughes G
Published: December 2014

1. Isometric tension was recorded in vitro from strips cut from the capsules of mesenteric lymph nodes of sheep. 2. One minute periods of field stimulation at frequencies of 1, 2, 4, 8 and 16 Hz (pulse duration, 0.3 ms) elicited tonic contractions of increasing force and duration. The stimulus frequency‐response relationship began to flatten out at frequencies greater than 4 Hz, where the response was already 72% of that at 16 Hz. 3. The response to field stimulation was abolished by tetrodotoxin (1 microM). 4. Phentolamine, rauwolscine and prazosin (all 1 microM) reduced the response to field stimulation, while desipramine (1 microM), potentiated it. 5. Atropine (1 microM) was without effect on the response. 6. These results suggest that sheep mesenteric lymph node capsules have a noradrenergic innervation which modulates their tone via an action on alpha‐adrenoceptors.
The calcium‐dependent potassium conductance in rat sympathetic neurones.
Authors: Belluzzi O , Sacchi O
Published: December 2014

1. Adult and intact sympathetic neurones of isolated rat superior cervical ganglia were subjected to a two‐electrode voltage‐clamp analysis at 37 degrees C in order to investigate the Ca2(+)‐dependent K+ conductance. 2. At each potential a Ca2(+)‐dependent K+ current, IKCa, was determined as the difference between the current that could be attributed to the voltage‐dependent K+ current, IKV, following Ca2+ channel blockade by Cd2+ and the total current generated. The final IKCa curves were obtained after correcting the experimental tracings for the underlying ICa current component. 3. IKCa became detectable during commands to ‐30 mV. About 3.6 x 10(5) Ca2+ ions are required to enter the cell before IKCa is initiated. The current was modelled on the basis of a 0.4‐0.6 ms delay followed by an exponential activation of a fast component, IKCaf, simultaneously with a much slower exponential activation, IKCas. Experiments indicate a sigmoidal activation curve for the fast conductance, gKCf, with half‐maximal activation at ‐13.0 mV and a slope factor of 4.7 mV (for 5 mM‐Ca2+ in the bath). The associated time constant, tau kcf, ranged from 0.8 to 2.0 ms. The slow conductance exhibited a similar steady‐state activation curve but an activation time constant in the 48‐280 ms range. The maximum mean gKC was 0.32 microS per neurone for either the fast or slow component. 4. Excess K+ ions accumulate in the perineuronal space during K+ current flow giving rise to rapidly occurring, large K+ reversal potential (EK) modifications (up to ‐45 mV for the largest currents). The kinetics of K+ extracellular load can be described satisfactorily by a simple exponential function (tau = 0.9‐2.8 ms). The characteristics of K+ wash‐out appear similar to those of accumulation. 5. The immediate effect of such an extracellular K+ build‐up is to make the apparent IKCa activation kinetics faster and to reduce (up to 50%) the true value of the K+ conductance. We simulated the predictions of a K+ diffusion model and generated new functions describing the IKCa steady‐state activation, activation rate and maximum conductance values which satisfactorily reconstruct the IKCa current tracings together with the K+ accumulation process near the membrane. 6. A small component of the Ca2(+)‐dependent K+ current, IAHP, was observed which survived at membrane potential levels negative to ‐40 mV. Increasing Ca2+ influx by applying longer pulses enhanced IAHP, which on the other hand was also activated by depolarizations of short duration.(ABSTRACT TRUNCATED AT 400 WORDS)
Direct excitation of rat spinal motoneurones by serotonin.
Authors: Takahashi T , Berger A J
Published: December 2014

1. The effects of serotonin (5‐HT) on visually identified motoneurones were investigated using the whole‐cell recording technique in a neonatal rat spinal cord slice preparation. 2. In current‐clamp recordings, bath application of 5‐HT depolarized motoneurones. This effect was observed after synaptic inputs were abolished by replacing external Ca2+ with Mg2+. 3. In voltage‐clamp recordings at holding potentials of ‐70 to ‐90 mV, 5‐HT induced an inward current (I5‐HT) in motoneurones in a Ca2(+)‐free‐Mg2+ solution containing tetrodotoxin. This inward current was accompanied by an increase in membrane conductance, which was prominent at voltages negative to the holding potential. 4. The inward I5‐HT response declined with repeated short applications of 5‐HT. I5‐HT produced by a single prolonged application (5 min) was only slightly diminished during the application period. 5. The minimum effective dose of 5‐HT for initiating the inward I5‐HT was less than 10 nM. At 10 microM, I5‐HT approached maximal levels. The averaged dissociation constant (Kd) for 5‐HT was approximately 120 nM. 6. Application of spiperone, the mixed 5‐HT1A, 5‐HT2 receptor antagonist, blocked the inward I5‐HT. Application of (+)‐8‐OH‐dipropylaminotetralin (8‐OHDPAT), a 5‐HT1A agonist, mimicked the action of 5‐HT. 7. Various K+ channel blockers including tetraethylammonium chloride (30 mM), 4‐aminopyridine (4 mM) and apamin (100 nM) did not abolish I5‐HT. Application of extracellular Cs+ (10 mM) blocked I5‐HT. 8. Peak inward I5‐HT became larger with increasing extracellular K+. With low Cl‐ pipette solution (less than 1 mM), or in low extracellular Na+ solution (26 mM), the inward I5‐HT was not abolished. 9. The current‐voltage relation of I5‐HT displayed inward rectification. In high external K+ concentration (20 mM), the reversal potential was about ‐29 mV, which is close to that of the inward rectifier evoked in motoneurones by membrane hyperpolarization. 10. The current generated by 5‐HT displayed similar characteristics to the inward rectifying current induced in motoneurones by membrane hyperpolarization. It is thus suggested that the 5‐HT‐induced current is possibly mediated by the intrinsic inward rectifier conductance.
Synaptic inhibition in the rat hippocampus in vivo following stimulation of the substantia nigra and ventral tegmentum.
Authors: Spencer P M , Wheal H V
Published: December 2014

1. The effects of stimulating the substantia nigra (SN) or the ventral tegmental area (VTA) on the excitability of cells in the rat hippocampal formation have been investigated in vivo. 2. A train of conditioning stimuli to either of the midbrain nuclei produced inhibition of evoked population spikes recorded in the CA1 pyramidal cell layer of the hippocampus. 3. These trains of pulses had no effect on the evoked synaptic field potential recorded in the stratum radiatum although they were effective in suppressing glutamate‐induced firing of cells in the hippocampus. These observations suggest that the inhibition is mediated through a postsynaptic mechanism. 4. The inhibition of the test population spike was observed at a latency of 50 ms after the conditioning train to either the SN or the VTA but did not reach a maximum until 300‐500 ms and 500‐750 ms post‐conditioning, respectively. The total duration of the inhibition in each case was about 5 s. 5. Following stimulation of the VTA, comparable levels of inhibition were recorded in the ventral and dorsal hippocampus. However, after stimulation of the SN, significantly less inhibition was observed in the ventral hippocampus. 6. Unlike the effects on the commissural‐evoked population spike in CA1, stimulation of SN or VTA had no effect on perforant path‐induced granule cell excitability in the dentate gyrus. 7. These results suggest that activity in the substantia nigra or ventral tegmental areas could have a powerful regulatory or feedback role in suppressing hippocampal excitability.
Endothelin augments unitary calcium channel currents on the smooth muscle cell membrane of guinea‐pig portal vein.
Authors: Inoue Y , Oike M , Nakao K , Kitamura K , Kuriyama H
Published: December 2014

1. The effects of endothelin (ET) on the Ca2+ channel current in smooth muscle cells of the guinea‐pig portal vein were investigated using the patch‐clamp technique with whole‐cell and cell‐attached configurations. 2. ET augmented the macroscopic Ba2+ current in a dose‐dependent manner; this effect was inhibited by nifedipine or Cd2+. Augmentation of the inward current by ET did not depend on the amplitude of the depolarizing pulse. Further, when the membrane potential was held at ‐60 mV, ET increased the amplitude of the Ba2+ inward current measured at the peak and end of the depolarizing pulse to the same extent. 3. By contrast, when the membrane potential was held at ‐80 mV, depolarizing pulses to potentials more negative than 0 mV produced greater augmentation of the inward current than did those more positive than 0 mV. Moreover, when a depolarizing pulse to below 0 mV was applied, ET increased the peak amplitude of the inward current more than the amplitude measured at the end of pulse. 4. Using the patch‐clamp technique with cell‐attached configuration, two types of unitary Ba2+ current with conductances of 22 and 12 pS were obtained in 50 mM‐Ba2+ solution. Nifedipine inhibited both types of unitary channel current, but the sensitivity of the 22 pS Ca2+ channel to nifedipine was 20‐fold higher than the 12 pS Ca2+ channel. 5. Bath application of ET prolonged the mean open time, reduced the number of sweeps in which no Ca2+ channel was opened ('blank' sweep), and increased the number of channel openings evoked by each depolarizing pulse without changes of conductance. As a consequence, ET increased the open probability of both channels. 6. Augmentation of the 12 pS channels by ET was seen only in the early phase of a depolarizing pulse (57 ms from the onset of 170 ms pulse), while augmentation of the 22 pS channels was seen during the entire period of a depolarizing pulse. 7. When ET was added to the pipette solution, the activity of both Ca2+ channels was increased. However, this effect was less frequently observed than when ET was applied in the bath. 8. These results suggest that ET augments both the nifedipine‐sensitive and resistant Ca2+ channels in the smooth muscle cell membrane of the guinea‐pig portal vein, but in different ways. Presumably, ET acts indirectly on the voltage‐dependent Ca2+ channel.
Intraburst kinetic properties of the GABAA receptor main conductance state of mouse spinal cord neurones in culture.
Authors: Twyman R E , Rogers C J , Macdonald R L
Published: December 2014

1. The intraburst kinetic properties of the main conductance state of gamma‐aminobutyric acidA (GABAA) receptor channels in excised outside‐out patches obtained from somata of mouse spinal cord neurones in cell culture were investigated using the patch clamp single‐channel recording technique. 2. At 2 microM‐GABA, the burst duration distribution was fitted by four exponential functions with time constants of 0.5, 2.4, 8.3 and 31.8 ms. 3. At 0.5, 1 and 2 microM‐GABA, frequency distribution histograms of the number of apparent openings per burst were best fitted by three geometric functions with similar mean numbers (1.1, 1.9 and 3.6) of openings per burst. The proportion of bursts with a mean of 1.1 openings per burst decreased with increased GABA concentration while the proportion of bursts with means of 1.9 and 3.6 openings per burst increased with GABA concentration. 4. Analyses of GABA receptor channel intraburst kinetics were performed at all three GABA concentrations. The results were similar for all concentrations, but detailed results are presented only for 2 microM‐GABA. 5. The open time distribution for all intraburst openings was best fitted by three exponential functions with time constants of 0.6, 2.9 and 8.9 ms. 6. Intraburst open time and total open time distributions for bursts with one to five openings were fitted with two or three exponential functions or gamma distributions, respectively. The number of components, time constants and relative areas were similar for both distributions. 7. The distributions of open times for the nth opening within bursts of k openings were similar for bursts containing two to five openings. The distributions of open times for the nth opening of all bursts varied with position within the burst. The distributions shifted to longer openings as the opening number increased from one to five. 8. The distributions of all closings within all bursts or within bursts with two to five openings and of closings relative to position in all bursts could be fitted by two exponential functions with time constants of about 0.20 and 3.1 ms and relative proportions of 0.55 and 0.45 at all GABA concentrations. 9. The total closed time distributions for bursts containing two to four closings, however, were all best fitted with only a single gamma distribution with a time constant of 1.3 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Alpha‐adrenergic modulation of the transient outward current in rabbit atrial myocytes.
Authors: Fedida D , Shimoni Y , Giles W R
Published: December 2014

1. A whole‐cell voltage‐clamp technique has been used to study the alpha‐effects of the adrenergic agonists noradrenaline, methoxamine and phenylephrine on the action potentials and membrane currents of rabbit atrial myocytes. Experiments were carried out at 22‐23 degrees C. 2. In the presence of 10(‐6) M‐propranolol, all three agents prolonged action potential duration. This change could be ascribed principally to changes in membrane current early during the plateau phase of the action potential. In the presence of 10(‐3) M‐4‐aminopyridine, no changes in calcium current (ICa) were observed on exposure to alpha‐agonists. No significant shift in the voltage dependence or change in the amplitude of the calcium current‐voltage relation was observed. 3. Exposure to 3 x 10(‐4) M‐CdCl2 to block ICa reduced the action potential prolongation caused by alpha‐adrenergic agonists. Measurement of unloaded cell shortening revealed that action potential prolongation caused by alpha‐agonists, especially at low stimulus rates, could contribute significantly to the positive inotropic effect of alpha‐adrenoceptor stimulation. 4. The voltage‐activated transient outward current (It) was markedly reduced during exposure to alpha‐adrenergic agonists in a dose‐dependent manner in the presence of CdCl2 (3 x 10(‐4) M) and propranolol in sufficient concentration to prevent beta‐adrenoceptor activation. Noradrenaline exhibited a higher potency for this effect than either methoxamine or phenylephrine. The noradrenaline concentration required to give 50% of the maximal effect was 6 x 10(‐6) M compared with 2.3 x 10(‐4) M for methoxamine. Noradrenaline reduced It by only about 60% of the maximum reduction produced by methoxamine suggesting that it could be classified as a partial agonist for this effect. 5. The reduction of It during exposure to alpha‐adrenergic agonists was rate dependent in that larger current reductions were observed at very low rates of stimulation (less than 0.1 Hz). 6. The magnitudes of current‐voltage relations for It were reduced over the entire voltage range studied during exposure to alpha‐adrenergic agonists and reductions were dose dependent. No shift of these relations along the voltage axis was observed. 7. The steady‐state inactivation relations for It were studied using two voltage clamp protocols. A two‐step method resulted in a relatively steep sigmoid ‘quasi‐steady‐state’ relation. The half‐inactivation potential of ‐27 mV was unaffected by alpha‐adrenergic agonists.(ABSTRACT TRUNCATED AT 400 WORDS)
Accuracy of weight estimation for weights lifted by proximal and distal muscles of the human upper limb.
Authors: Gandevia S C , Kilbreath S L
Published: December 2014

1. It is well established that tactile acuity is greater over digits than over the proximal parts of the upper limb and that the corticospinal projection is especially dense for distal muscles. To determine whether the acuity for judgements of forces exerted by distal muscles differed from that for proximal muscles, a weight‐matching task was used with first dorsal interosseous, flexor pollicus longus and elbow flexors. 2. Reference weights equivalent to approximately 3% (light) and 15% (heavy) of the maximal voluntary contraction were lifted by one muscle group on the left. They were matched with a variable weight, lifted by the same group, on the right. 3. In naive subjects, the coefficient of variation for repeated estimates of perceived heaviness was significantly lower for proximal than distal muscles. Measured in this way, ‘accuracy’ (i.e. reproducibility of the estimates) was not greater for the intrinsic muscles of the hand. This result could not be explained by the way in which the weights were supported by the index finger. When the data were expressed as the relative difference between the reference and the matched weight, each muscle group behaved similarly. 4. For a particular muscle, accuracy was greater when the heavy rather than the light weights were lifted. 5. Given that estimates of forces and heaviness are biased by signals of central motor command (McCloskey, 1981; Gandevia, 1987; Cafarelli, 1988; Jones, 1988). these signals could be graded no more finely for distal than proximal muscles. Furthermore, relative accuracy was greater for forces at the high rather than the low end of the comfortable ‘matching’ range of force for a particular muscle.
Some characteristics of the functioning of membrane receptor‐channel complexes of Limnaea stagnalis neurones.
Authors: Panarin V A , Kondratyev V A , Rayevsky O A
Published: December 2014

1. Limnaea stagnalis neurones have been used to study the functioning of membrane receptor‐channel complexes. The experiments were performed using a fixed membrane potential (E) and the intracellular perfusion technique. The cells employed responded to acetylcholine (ACh) by changing only their Cl‐ conductance. 2. ACh‐induced currents, their fluctuations and relaxations resulting from a jump of E were studied. 3. The following facts have been established based on analysis of ACh currents, their fluctuations and relaxations: (1) the characteristic time of the exponential decay of the autocorrelation function, tau N, is in the range of 15‐20 ms; (2) the characteristic relaxation time, tau R, equals 50‐60 ms (ACh concentration = 0.25 microM, desensitization is not observed); (3) E does not exert any functionally significant effect upon tau N or tau R which could have governed the non‐linearity of the membrane voltage‐current characteristic; (4) variation of ACh concentration from 0.25 to 1 microM has a significant effect on tau R but not on tau N; (5) lowering of the ACh solution temperature from 22 to 8.5 degrees C results in a 20% increase of the ACh current, a 3‐ to 4‐fold decrease of the single‐channel conductance (gamma), a 20% increase in tau N and a 3‐ to 4‐fold increase in tau R. 4. The suberylcholine (SCh)‐induced membrane current has approximately the same value as the ACh‐induced current at equal concentrations of ACh and SCh (0.25 microM); the tau N and gamma values were also quite close, but tau R was 2.3 times lower for SCh than for ACh. 5. An essentially two‐stage scheme of functioning of membrane receptor‐channel complexes is proposed. The scheme has two distinguishable and measurable stages and involves five closed states and one open state; it offers an explanation for our experimental data as well as the results of other workers.
Regulation of mucus secretion by cells isolated from the rat gastric mucosa.
Authors: Keates A C , Hanson P J
Published: December 2014

1. A suspension of cells, containing about 30% mucous cells, was isolated from the rat fundic mucosa, and was pre‐incubated with D‐[6‐3H]glucosamine. 3H‐labelled material subsequently released into the medium was separated by Fast Protein Liquid Chromatography on a Superose 6 column. 2. A sharp peak of labelled high molecular weight material eluted from the column close to the void volume. This material was identified as mucous glycoprotein by its similar chromatographic behaviour to partially purified rat gastric mucous glycoprotein, by its resistance to complete degradation by papain and by its behaviour on treatment with dithiothreitol. On a caesium chloride density gradient the labelled material was virtually all located between densities of 1.35 and 1.53 g/ml. with the main peak at 1.40 g/ml. 3. A broad peak of lower molecular weight material was also eluted from the column. The release of this unidentified material did not seem to be closely associated with the release of mucous glycoprotein from the cells. 4. Release of mucous glycoprotein was stimulated by secretin (half‐maximally effective concentration 2.3 nM, 84% stimulation above basal release at 100 nM), and by isoprenaline (half‐maximally effective concentration 34 nM, 33% stimulation at 1 microM). Carbachol (0.5 nM) produced a significant (18‐29%) stimulation of mucus secretion, but gastrin (100 nM), histamine (0.5 mM) and epidermal growth factor (200 nM) were without effect. 5. The preparation should prove useful in the identification of the agents which regulate gastric mucus secretion.
The whole‐cell Ca2+ channel current in single smooth muscle cells of the guinea‐pig ureter.
Authors: Lang R J
Published: December 2014

1. Calcium channel currents were recorded in single, enzymatically isolated smooth muscle cells of the guinea‐pig ureter using a single‐electrode whole‐cell voltage clamp technique. Calcium and barium currents through voltage‐activated Ca2+ channels were recorded in cells dialysed with Cs(+)‐ or Na(+)‐containing saline which suppressed K+ currents. 2. Inward currents in Ca2+ (1.5‐7.5 mM) or Ba2+ (1.5‐7.5 mM) were recorded at potentials positive to ‐50 to ‐30 mV. Inward currents were maximal at 0 mV in 1.5 mM‐Ca2+ and at +10 mV in 7.5 mM‐Ba2+. Current flow through Ca2+ channels in Cs(+)‐filled cells (in 1.5 mM‐Ca2+ or 7.5 mM‐Ba2+) changed from inward to outward at potentials positive to +70 mV. In Na(+)‐filled cells this reversal potential was between +50 and +60 mV. 3. Replacing Ca2+ or Ba2+ with Co2+ (1.5 mM) blocked all inward current flow through these Ca2+ channels; outward currents at potentials positive to +40 mV, however, were increased. Cadmium (100 microM) and nifedipine (0.1‐10 microM) reduced both inward and outward current flow. 4. Calcium channel activation showed a sigmoidal relationship with membrane potential; the potential of half‐maximal activation was ‐8.4 mV in 1.5 mM‐Ca2+ and ‐10.8 mV in 7.5 mM‐Ba2+. The maximum membrane conductance to Ca2+ (in 1.5 mM‐Ca2+) was 2.57 nS/cell or approximately 0.05 mS/cm2. 5. Evidence for a voltage‐dependent inactivation mechanism included (a) the time‐dependent relaxation of the outward currents at potentials positive to the reversal potential and (b) a steady‐state inactivation (f infinity (V] vs. membrane potential relationship (in 7.5 mM‐Ba2+) which ranged between ‐80 and 0 mV, with a half‐maximal availability at ‐40.5 mV. 6. The voltage dependencies of the inward current elicited from ‐80 and ‐30 mV were similar, suggesting that depolarization activated only L‐type Ca2+ channels. 7. It was concluded that the processes controlling the time course of the Ca2+ current in single ureteral cells bathed in physiological concentrations of Ca2+ were mostly voltage‐dependent.
Acetylcholine release at identified nerve terminals in the organ‐cultured frog neuromuscular preparation.
Authors: Cherki‐Vakil R , Meiri H
Published: December 2014

1. The frog cutaneous pectoris neuromuscular preparation was maintained in organ culture for a few days, at either 24 or 14 degrees C. The synaptic activity of identified nerve terminals was repeatedly examined in order to describe the sequence and time course of changes from normal synaptic activity to a complete synaptic silence. 2. We found that the ‘transient stage’ (stage II, according to Ko, 1981) consists of at least three distinct periods each characterized by a unique trend of change in synaptic activity. The initial change involved a simultaneous decay of both spontaneous and nerve stimulation‐evoked release of acetylcholine (sub‐stage II1). Subsequently, the frequency of spontaneous miniature endplate potentials (MEPPs) increased gradually, while the evoked release continued its monotonous decay (sub‐stage II2). During the third sub‐stage spontaneous MEPPs, but no evoked endplate potentials (EPPs), were observed (sub‐stage II3). 3. Statistical properties of acetylcholine release in still‐transmitting junctions at sub‐stage II2 and in non‐transmitting junctions at sub‐stage II3 were investigated. MEPPs with skewed amplitude histograms and bursting behaviour were evident at both sub‐stages. However, the incidence and the extent of these distortions were higher in the non‐transmitting junctions. 4. An inverse relation between the quantal content of evoked release and the rate of spontaneous secretion was found in the transmitting junctions. 5. These results suggest that some of the deterioration of synaptic activity in organ culture is caused by an impairment of the release process itself. Possible cellular mechanisms are discussed.
Diabetes mellitus and sugar transport across the brush‐border and basolateral membranes of rat jejunal enterocytes.
Authors: Debnam E S , Ebrahim H Y , Swaine D J
Published: December 2014

1. The effects of streptozotocin‐induced diabetes mellitus on active jejunal glucose uptake in vivo, and on galactose movement across the brush‐border (phlorhizin‐sensitive) and basolateral (phlorhizin‐insensitive) membranes of isolated upper and mid‐villus enterocytes has been studied. 2. Chronic diabetes increased unidirectional phlorhizin‐sensitive galactose uptake by mid‐villus but not upper villus cells. In contrast, phlorhizin‐insensitive uptake by both cell populations was enhanced by diabetes. 3. Diabetes increased glucose absorption in vivo by mechanisms which were unrelated to hyperphagia. Mucosal hyperplasia acting together with an epithelium containing a higher proportion of mature enterocytes is the most likely explanation for the response. 4. We conclude that, during diabetes, the mid‐villus region is an important site of adaptation with functional changes occurring at both the brush‐border and basolateral membranes. The increased hexose transport ability of the basolateral membrane is retained during cell transit along the villus.
Intracellular calcium ions modulate acetylcholine‐induced inward current in guinea‐pig ileum.
Authors: Inoue R , Isenberg G
Published: December 2014

1. The modulatory effect of internal Ca2+ on the current through the ACh‐activated non‐selective cation channels (Ins, ACh) was investigated by the whole‐cell patch clamp technique in single isolated cells of guinea‐pig ileum. 2. Ins, ACh was isolated with caesium aspartate internal solution of low Ca2(+)‐buffering capacity (10 microM‐EGTA). With preceding depolarizations which evoked voltage‐operated Ca2+ currents (ICa), Ins, ACh increased in amplitude and decayed more rapidly. The extent of this ‘facilitating’ effect depended on the number and duration of the depolarizations. 3. When depolarizing pulses were applied during the sustained phase of Ins, ACh, they were followed by large inward tail currents. These tail currents (tail Ins, ACh) resembled the non‐facilitated Ins, ACh recorded without the depolarizing pulse, in regard to voltage‐dependent gating and dependence on the extracellular Na+ concentration, thus suggesting that the currents are flowing through the same class of channels. 4. The tail Ins, ACh was apparently composed of two components distinguished by the insensitivity to organic Ca2+ antagonists. The minor component (about 20% of tail Ins, ACh) showed a rapid decay (about 150 ms at ‐60 mV) which could be attributed to voltage‐dependent kinetics. The major component decayed slowly within 5 s and appeared to be related to changes in the intracellular Ca2+ concentration. The latter component was not recorded when Ba2+ or Sr2+ were used as a charge carrier for ICa and was blocked by 10 microM‐D600 or nitrendipine, or Cd2+ 0.2‐0.5 mM). 5. The tail Ins, ACh increased in proportion to Ca2+ influx when the duration of depolarizing pulses were prolonged from 15 to 200 ms, but this ‘facilitating’ effect was greatly suppressed when the cell was perfused with 40 mM‐EGTA. 6. When the pCa in the pipette was varied using 40 mM‐Ca‐EGTA, the conductance through Ins, ACh increased in a manner dependent on intracellular Ca2+ concentration. Half‐maximal and submaximal activation occurred at about 200 nM and 1 microM, respectively. 7. These results show that the activity of Ins, ACh is very sensitive to the intracellular Ca2+ concentration in the physiological range.
Cation transport by sweat ducts in primary culture. Ionic mechanism of cholinergically evoked current oscillations.
Authors: Larsen E H , Novak I , Pedersen P S
Published: December 2014

1. The coiled reabsorptive segment of human sweat ducts was cultured in vitro. Cells were then harvested and plated onto a dialysis membrane which was glued over a hole in a small disc. Cultures were maintained in a low serum, hormone‐supplemented medium that allowed the cells to grow to confluency. The disc was then placed as a partition between two compartments of a miniature Ussing chamber. The chamber was mounted on the stage of an inverted microscope and intracellular potentials were recorded under transepithelial open‐circuit or voltage clamp conditions. All values are given as means +/‐ S.E.M. and n refers to the number of preparations or duct cells. 2. Under control conditions, the cultured epithelia developed mucosa‐negative transepithelial potentials (Vt) ranging from ‐2.5 to ‐38 mV (‐13.5 +/‐ 1.5 mV, n = 36). The basolateral membrane potential (Vb) was ‐39.4 +/‐ 0.7 mV (n = 50 cells), and the apical membrane potential (Va) was linearly correlated with Vt:Va = 1.0 Vt ‐39.3 mV (r = ‐0.78, n = 50). 3. The epithelium generated inwardly directed short‐circuit currents (Isc) of 12‐95 microA cm‐2 (45 +/‐ 4 microA cm‐2, n = 36) with a steady‐state intracellular potential. Vc = ‐31.1 +/‐ 0.6 mV and a fractional resistance of the apical membrane, fR = 0.59 +/‐ 0.01 (n = 115 cells). 4. The Na+ channel blocker amiloride (mucosal bath, 10 microM) abolished Isc ‐0.8 +/‐ 0.6 microA cm‐2), the cells hyperpolarized to ‐61.0 +/‐ 1.2 mV, and fR increased to 0.85 +/‐ 0.01 (n = 44). These effects were fully reversible. 5. During initial stimulation with the cholinergic agonist, methacholine (serosa, 5 or 10 microM), the short‐circuit current increased to 80 +/‐ 10 microA cm‐2, the cells hyperpolarized to ‐55.8 +/‐ 1.2 mV, and fR increased to 0.82 +/‐ 0.01 (n = 35). 6. In short‐circuited preparations stimulated with methacholine an increase in mucosal potassium concentration ([K+]m) from 5 to 25 mM had no significant effect, while a similar increase in the serosal K+ concentration ([K+]s) produced a change in Vc of 44 +/‐ 3 mV per log10[K+]s (n = 9). In non‐stimulated preparations this change was only 16 +/‐ 2 mV per log10[K+]s (n = 13). After blocking the apical Na+ channels with amiloride the slope was 24 +/‐ 5 mV per log10[K+]s in unstimulated preparations.(ABSTRACT TRUNCATED AT 400 WORDS)