bluuebunny/crossref_metadata_2025 huggingface dataset:
Reorganization of sympathetic preganglionic connections in cat bladder ganglia following parasympathetic denervation.
Authors: de Groat W C , Kawatani M
Published: December 2014

1. Experiments were undertaken to examine the mechanisms involved in the reorganization of sympathetic efferent pathways to the urinary bladder of the cat following chronic unilateral, parasympathetic preganglionic denervation of the bladder. 2. Electrical stimulation (10‐30 Hz) of the hypogastric nerve in cats with an intact bladder innervation or on the normally innervated side of the bladder in unilaterally denervated preparations elicited low‐amplitude (10‐25 cmH2O) transient (10‐30 s) bladder contractions and non‐synaptic axonal volleys on bladder postganglionic nerves. However, after chronic (3‐22 months) sacral preganglionic denervation, hypogastric nerve stimulation on the side of the denervation elicited large (60‐80 cmH2O) and more sustained (4‐5 min) bladder contractions as well as synaptically mediated firing on bladder postganglionic nerves. 3. The vesicoexcitatory effects of hypogastric nerve stimulation on the chronically denervated side were not altered selectively by the adrenergic blocking agent, phenoxybenzamine, but were blocked by atropine and hexamethonium suggesting that the responses were mediated by muscarinic and nicotinic cholinergic synapses. These drugs did not influence the responses elicited by hypogastric nerve stimulation on the normally innervated side of the bladder. 4. Following more extensive chronic unilateral denervation (transection of the pelvic and hypogastric nerves on one side of the bladder) stimulation of the contralateral intact pelvic nerve elicited postganglionic firing in vesical postganglionic nerves on the denervated side. This crossed excitatory pathway was not observed in normal animals or following sacral preganglionic denervation. 5. It is concluded that parasympathetic preganglionic denervation of the bladder ganglia leads to a reinnervation of the denervated cholinergic ganglion cells by sympathetic preganglionic pathways in the ipsilateral hypogastric nerve. This reinnervation results in the conversion of sympathetic inhibitory pathways to excitatory pathways in the denervated bladder. This change may contribute to the development of the autonomous hyperactive bladder seen under conditions of peripheral nerve or conus medullaris lesions of the spinal cord.
Anion channels with multiple conductance levels in a mouse B lymphocyte cell line.
Authors: Bosma M M
Published: December 2014

1. Multiple conductance level ion channels were recorded in excised and cell‐attached patches from cells of a mouse B lymphocyte hybridoma line. The reversal potential for the single‐channel current was unaffected by the species of cation on the cytoplasmic face of the patch, but changed as the Cl‐ concentration was altered, indicating that the channel is anion selective. 2. The permeability sequence determined from reversal potentials was F‐ greater than I‐ greater than SCN‐ greater than Br‐ greater than Cl‐ greater than glucuronate greater than NO3‐ greater than aspartate. This was different from the conductance sequence (Cl‐ greater than SCN‐ = F‐ greater than Br‐ greater than NO3‐ greater than I‐ greater than glucuronate greater than aspartate), indicating interaction of ions within the pore of the channel. Consistent with this was the observation of anomalous mole fraction dependence with a mixed solution of thiocyanate and chloride. 3. In addition to the main open level (about 400 pS; excised patch, symmetrical 165 mM‐Cl‐), three subconductance levels and one supraconductance level were observed. These were concluded to be integral components of the same channel based on coincidence of appearance and identical permeabilities. 4. The channel is voltage dependent, with open probability in excised patches increasing with more positive potentials. The channel was reversibly blocked in a voltage‐dependent manner by SITS (4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid), a stilbene derivative, on the cytoplasmic face. 5. Several differences were noted between cell‐attached and excised‐patch recordings. The multiple conductance level channel was less frequently seen in cell‐attached patches but could often be induced to appear by prolonged application of positive voltages. This induced channel in attached patches showed an altered voltage dependence which could be partially mimicked in excised patches by including cyclic AMP and ATP in the solution on the cytoplasmic side of the membrane.
Isometric force production before and after chemical skinning in isolated muscle fibres of the frog Rana temporaria.
Authors: Elzinga G , Stienen G J , Wilson M G
Published: December 2014

1. The force produced in single fibres isolated from the anterior tibialis muscle of the frog Rana temporaria has been measured in tetani near 4 degrees C, and then in calcium‐activated contractures of segments of the same fibres after chemical demembranation. All measurements were made at a sarcomere length of 2.3 microns. Force was normalized for fibre cross‐section by the dry weight per unit length of the segments, which is proportional to cross‐sectional area (Elzinga, Howarth, Rall, Wilson & Woledge, 1989). 2. The ratio of the force developed by the skinned segments to that produced by the intact fibres was inversely related to segment cross‐section (dry weight per unit length), falling from approximately 1.0 for the thinnest segments to 0.6 for the thickest segments. 3. It is calculated that the accumulation of orthophosphate ion within contracting segments can account for a significant part of the decline in relative force in thicker segments. 4. The absolute forces in intact fibres and their derived segments were strongly correlated, but normalization by segment cross‐section removed the correlation. 5. It is concluded that the sources of the approximately twofold variation in normalized force in both intact and skinned preparations are different. The existence of diffusible, force‐modulating factors in intact fibres, which may be removed during skinning, is considered.
Potassium channels involved in the transduction mechanism of dopamine D2 receptors in rat lactotrophs.
Authors: Castelletti L , Memo M , Missale C , Spano P F , Valerio A
Published: December 2014

1. Radioactive rubidium (86Rb+) efflux was used to measure potassium (K+) permeability in a study designed to asses both the presence and the sensitivity to ions and drugs of the K+ channels in the plasma membrane of rat lactotrophs. 2. Rb+ efflux from Rb+‐pre‐loaded lactotrophs into nominally calcium‐free solution containing 5 mM‐K+ was linear from 1 to 60 s, with a calculated rate of about 0.1%/s. Raising K+ concentrations to depolarize the cells stimulated the Rb+ efflux (0.2%/s), which was already significant after 1 s of exposure of the cell to 100 mM‐K+. This component of Rb+ efflux has been designated component V (sensitive to voltage and Ca2+ independent). 3. Addition of Ca2+ to 5 mM‐K+ solution had no effect on resting Rb+ efflux (0.1%/s), but did further stimulate Rb+ efflux into K+‐rich solutions. This component, which has been designated component C, was completely inhibited by 0.5 mM‐cadmium. These data fit the view that the increase in intracellular Ca2+ concentration during depolarization opens certain (Ca2+‐activated) K+ channels. 4. K+ efflux was differently affected by K+ channel blockers. Tetraethylammonium (TEA) inhibited both V and C components while 4‐aminopyridine (4‐AP) inhibited the component V without modifying the C component of Rb+ efflux. 5. Dopamine appears to affect both types of Rb+ efflux components. Dopamine increased the efflux of Rb+ in a nominally Ca2+‐free medium containing 5 mM‐K+ (component V). This effect was statistically significant 15 s after exposure of the cells to 10 nM‐dopamine. Increasing the concentrations of K+ to gradually depolarize the cells enhanced the rate of increase of Rb+ efflux induced by dopamine, being evident in the initial 2‐5 s of incubations. Dopamine also increased Rb+ efflux in a 5 mM‐K+ solution containing 1 mM‐Ca2+ (component C). This effect was rapid (2‐5 s) and inhibited by 0.5 mM‐cadmium. The combined action of dopamine on both component C and V caused the cells to be less sensitive to depolarizing concentrations of K+. The increase in Rb+ efflux and the enhancement of prolactin release induced by high concentrations of K+ were, indeed, prevented by exposure of the cells to 10 nM‐dopamine. 6. The effects of dopamine on either component V or component C were pharmacologically characterized as D2 receptor mediated, being mimicked by selective D2 receptor agonists (quinpirole and RU 24213) and stereospecifically blocked by the D2 receptor antagonist sulpiride.(ABSTRACT TRUNCATED AT 400 WORDS)
The consequences of simulated ischaemia on intracellular Ca2+ and tension in isolated ferret ventricular muscle.
Authors: Allen D G , Lee J A , Smith G L
Published: December 2014

1. In order to study cellular events occurring in ischaemia, we have developed a method for simulating ischaemia in an isolated papillary muscle. Muscles were suspended in a chamber and changed from conventional superfusion with Tyrode solution to gas perfusion with 95% N2/5% CO2 (N2 gas perfusion), thus simultaneously stopping oxygenation and flow. Surface cells of the preparation were injected with the photoprotein aequorin in order to monitor intracellular free calcium concentration [( Ca2+]i). 2. Gas perfusion with 95% O2/5% CO2 (O2 gas perfusion) had little effect on the tension or Ca2+ transients. Superfusion with Tyrode solution equilibrated with 95% N2/5% CO2 (N2 Tyrode) caused tension to decline to 30‐40% of control, but had little effect on the amplitude of the Ca2+ transients. N2 gas perfusion caused tension to fall more rapidly and to a lower level than superfusion with N2 Tyrode. Ca2+ transients showed a small initial decline followed by a slowly developing increase in magnitude and duration. 3. Long exposures to N2 gas perfusion caused tension to decline to very low levels and Ca2+ transients to increase to a maximum. After a variable length of time, resting tension began to increase. At approximately the same time, Ca2+ transients began to decrease and eventually disappeared. Resting Ca2+ increased during N2 gas perfusion and remained elevated when the Ca2+ transients had declined. These changes could be reversed by restarting superfusion with standard Tyrode or by perfusion with O2 gas. 4. N2 gas perfusion caused a depolarization of the resting potential and an abbreviation of the action potential. In a long exposure the action potential eventually failed. These changes could be reversed by restarting superfusion with standard Tyrode or by perfusion with O2 gas. 5. Many of the effects of N2 gas perfusion could be mimicked by the addition of 20 mM‐lactic acid to the superfusing solution, which caused a profound reduction of tension and also an increase in the amplitude and duration of the Ca2+ transients. Calculation of the changes in intracellular pH caused by the addition of lactic acid suggest that the fall in intracellular pH produced by lactic acid was similar to that occurring in ischaemia. 6. Repeated exposures to N2 gas perfusion caused tension to fall more rapidly and an increased resting tension to develop more rapidly. The slowly developing rise in Ca2+ transients was abolished and a rise in resting Ca2+ occurred more quickly. 7. When muscles were quiescent, exposure to N2 gas perfusion caused an increase in resting light.(ABSTRACT TRUNCATED AT 400 WORDS)
Expression of amino acid transport systems in cultured human umbilical vein endothelial cells.
Authors: Mann G E , Pearson J D , Sheriff C J , Toothill V J
Published: December 2014

1. Nutrient transport in cultured human umbilical vein endothelial cells was characterized using a rapid dual‐isotope dilution technique. Microcarrier beads with confluent endothelial cells were perfused in small columns, and uptake and efflux were assessed relative to D‐mannitol (extracellular tracer) during a single transit through the column. 2. At tracer concentrations significant unidirectional uptakes were measured for L‐leucine (53 +/‐ 2%), L‐phenylalanine (73 +/‐ 2%), L‐serine (40 +/‐ 4%), L‐arginine (42 +/‐ 3%) and L‐ornithine (26 +/‐ 3%). Uptake for L‐proline, D‐glucose, dopamine and serotonin was lower (6‐10%), whereas uptake for the system A analogue 2‐methylaminoisobutyric acid (2‐MeAIB) was negligible. Uptakes rapidly decreased with time due to tracer efflux. 3. Endothelial cell transport of L‐leucine was markedly inhibited during perfusion with 1 mM‐BCH (beta‐2‐aminobicyclo‐(2,2,1)‐heptane‐2‐carboxylic acid, system L analogue), L‐leucine, D‐leucine, L‐phenylalanine, L‐methionine and L‐DOPA. 2‐MeAIB, L‐cysteine, glycine, L‐proline, hydroxy‐L‐proline, L‐aspartate and beta‐alanine were poor inhibitors, while L‐serine and the cationic substrates L‐lysine and L‐arginine inhibited uptake by 10‐35%. 4. When the kinetics of L‐leucine transport were examined over a wide range of substrate concentrations (0.025‐1 mM) transport was saturable. A single entry site analysis gave a half‐maximal saturation constant Kt = 0.24 +/‐ 0.08 mM (mean +/‐ S.E.M., n = 5) and a Vmax = 27.8 +/‐ 4.6 nmol/min per column (approximately 3 x 10(6) cells). 5. Removal of sodium from the perfusate inhibited tracer uptake of L‐leucine, L‐serine and L‐arginine by respectively 20 +/‐ 5% (n = 3), 77 +/‐ 5% (n = 3) and 35 +/‐ 4% (n = 3). 6. Our results provide the first evidence that cultured human endothelial cells of venous origin express a saturable transport system for large neutral amino acids resembling system L described in brain microvascular endothelium. Detection of Na+‐dependent and Na+‐independent L‐arginine uptake is of interest in view of recent reports that this cationic amino acid may be the physiological precursor for nitric oxide released by endothelium.
Temperature and metabolic changes in rats after various doses of tumour necrosis factor alpha.
Authors: Bibby D C , Grimble R F
Published: December 2014

1. Sub‐lethal doses of recombinant of tumour necrosis factor alpha (TNF alpha) were administered i.v. to young conscious male Wistar rats. Temperature changes and alterations in serum zinc and albumin concentrations and weight and composition of liver, kidney, spleen, tibialis muscle and skin were measured. Temperatures were monitored for 8 h and tissue parameters 8 and 22 h post‐injection. 2. Doses above 10 micrograms/kg caused fevers of increasing magnitude and duration with latencies of 2 h. At doses of 200 micrograms/kg or more fevers were preceded by a fall in rectal temperature of up to 1.1 degrees C. 3. Weight loss by skin and tibialis and gain by liver occurred 22 h post‐injection. Spleen and kidney weight and zinc and spleen protein contents were unaffected. Serum albumin and zinc fell 22 and 8 h after injection respectively. Liver zinc was elevated at both times and inversely correlated at 8 h with serum values. A degree of dose dependence of zinc and albumin changes existed. A gain in protein was evident in liver 8 h post‐injection and a loss by muscle at 22 h. Paradoxical effects were observed in skin protein concentration. 4. TNF alpha mimicked many of the metabolic effects of E. coli endotoxin reported in the literature and showed similar effects to those described for interleukin 1 (IL1).
The inactivating K+ current in GH3 pituitary cells and its modification by chemical reagents.
Authors: Oxford G S , Wagoner P K
Published: December 2014

1. Whole‐cell and single‐channel recording techniques were applied to the study of the permeability and gating of inactivating K+ channels from clonal pituitary cells. 2. The cation selectivity sequence (measured from reversal potentials) for the channels underlying the inactivating K+ current was Tl+ greater than K+ greater than Rb+ greater than NH4+. The conductance sequence (determined from current amplitudes) was K+ = Tl+ greater than Rb+ greater than NH4+. 3. The inactivating current (IK(i] which was blocked by 4‐aminopyridine (4‐AP), activated at voltages more positive than ‐40 mV and half‐inactivated at that voltage. Inactivation proceeded as the sum of two exponentials with mean time constants of 21 and 82 ms. Deactivation followed a single‐exponential time course. 4. Recovery from inactivation was slow, voltage dependent and multi‐exponential, taking more than 50 s near the cell's resting potential. 5. The magnitudes of outward current and of slope conductance increased as the concentration of external K+ was increased. 6. On‐cell and outside‐out membrane patches revealed minicurrents with gating and pharmacological properties identical to whole‐cell currents. Single channels with inactivating characteristics, while rarely observed, had an average slope conductance of 6‐8 pS. 7. Intracellular application of the disulphonic stilbene derivative, SITS, and the protein‐modifying reagent, N‐bromoacetamide (NBA), at concentrations of 0.2‐1 mM for several tens of minutes dramatically slowed the decay (inactivation) of K+ currents and caused coincident increases in the magnitude of outward IK(i). 8. Extracellular application of NBA at much lower concentrations (1‐100 microM) and much shorter exposure times (1‐30 s) also slowed inactivation. This effect was reversible for brief applications at low doses, but became irreversible after longer exposures. 9. Both internal and external NBA shifted the steady‐state inactivation‐voltage relation by +10 mV and reduced inactivation at voltages more positive than 0 mV. 10. The efficacy of external NBA was independent of holding potential between ‐80 and 0 mV. 11. Potassium minicurrents and single channels recorded from on‐cell membrane patches were not affected by application of NBA to the extrapatch membrane. In contrast, NBA reversibly slowed the decay, increased the magnitude of minicurrents and prolonged the open times of single K+ channels recorded from outside‐out patches. The single‐channel conductance was unchanged by NBA.(ABSTRACT TRUNCATED AT 400 WORDS)
Facilitation of individual gamma‐motoneurones by the discharge of single slowly adapting type 1 mechanoreceptors in cats.
Authors: Davey N J , Ellaway P H
Published: December 2014

1. Cross‐correlation of the discharges of individual neurones has been used to investigate the influence of identified cutaneous afferents on gamma‐motoneurones below the level of complete spinal section in decerebrated cats. Discharges of single, sural nerve afferents from the heel were recorded in the dorsal root ganglia. Discharges of gamma‐motoneurones were recorded from cut filaments of the muscle nerve to gastrocnemius medialis of the same leg. gamma‐Motoneurones had a background discharge in the absence of intentional stimulation. 2. Correlograms involving slowly adapting afferents were formed during steady application of a probe to the receptive field for repeated periods of 10 s. Afferent synchronization was minimized by rejecting any period of probe movement. Correlograms involving rapidly adapting afferents required continuous movement of the probe to sustain afferent discharge. 3. Statistically significant primary peaks in correlations were observed for twenty‐one pairings of gamma‐motoneurones with seventeen out of thirty‐nine slowly adapting, type 1 (SA1) mechanoreceptors. Primary peaks had widths at half‐maximum in the range of 2‐7 ms. No such short duration peaks were seen for fourteen pairings of gamma‐motoneurones with eleven slowly adapting type 2 (SA2) receptors or for thirty‐five pairings with twenty‐nine hair follicle (HF) afferents. Broad correlations with peaks extending over tens of milliseconds were seen for HF afferents and could be generated in correlograms for slowly adapting afferents by moving the probe. 4. The short duration peaks were delayed with respect to the SA1 afferent discharges. Subtraction of peripheral conduction times gave central delays for the increased probability of gamma‐motoneurone firing ranging from 2.7 to 6.5 ms (mean = 4.0 ms). These values were not significantly different from the central delays of gamma‐motoneurone excitation in response to electrical stimulation of the sural nerve at a strength 1.2 times threshold. 5. The increase in probability of gamma‐motoneurone discharge given a single SA1 afferent discharge ranged from 0.005 to 0.156 with a mean value of 0.052. The rise time of the peak ranged from 1 to 4 ms with a mean value of 1.9 ms (n = 9). 6. The properties of the correlogram peaks were not related to the axon conduction velocity of either the SA1 afferent or gamma efferent neurones. 7. The SA1 afferents that facilitated gamma‐motoneurone discharge had axon conduction velocities in the range 29‐81 m/s and could not be distinguished from SA1 afferents lacking correlations.(ABSTRACT TRUNCATED AT 400 WORDS)
Kinetics of the membrane current mediated by serotonin 5‐HT3 receptors in cultured mouse neuroblastoma cells.
Authors: Neijt H C , Plomp J J , Vijverberg H P
Published: December 2014

1. Ionic currents mediated by serotonin 5‐HT3 receptors were studied in the mouse neuroblastoma cell line N1E‐115, using suction pipettes for intracellular perfusion and voltage clamp recording. The dependence of the kinetics of the membrane current on serotonin concentration was investigated. 2. At a holding potential of ‐70 mV application of 5‐HT (5‐hydroxytryptamine creatinine sulphate) causes a transient inward current. The i‐V curve of the peak amplitude is linear between ‐80 and 60 mV. The reversal potential is 20 +/‐ 4 mV (mean +/‐ S.D.). The kinetics of the transient ionic current are independent of the holding potential. 3. In the presence of 5‐HT the membrane current decays to a small steady‐state level with a single‐exponential time course. The time constant of decay decreases with increasing concentration of the agonist, to a minimum value of 6.5 +/‐ 1.5 s for concentrations of 5‐HT greater than or equal to 3 microM. 4. When the agonist is rapidly removed, single‐exponential decay of the ionic current is observed. The time constant of this decay in the absence of 5‐HT amounts to 6.9 +/‐ 1.5 s and is independent of the membrane potential and of the concentration of 5‐HT used. 5. In the presence of low concentrations of 5‐HT the peak amplitude of the inward current evoked with a high concentration of agonist is gradually reduced. The onset of this desensitization follows the same time course as the decay of the membrane current. In the range from 0.7 to 1.5 microM‐5‐HT both kinetic processes show the same steep concentration dependence. 6. Recovery from desensitization, measured at variable intervals after removal of the agonist, can be fitted by a single‐exponential function with a time constant of 18 +/‐ 4 s. 7. The results show that the kinetic properties of the 5‐HT3 receptor‐mediated ionic current can only be described by a complex, co‐operative model.
Cultured melanotrophs of the adult rat pituitary possess a voltage‐activated fast transient outward current.
Authors: Kehl S J
Published: December 2014

1. Whole‐cell voltage‐clamp recordings were made from cultured melanotrophs obtained from adult rats and maintained in vitro using conventional cell culture procedures. 2. The outward current recorded in the presence of Na+ and Ca2+ channel blockers was normally comprised of two components: a slowly activating, slowly inactivating current (IK(s] and a fast transient current (IK(f]. The selective blockade of IK(s) by 20 mM‐tetraethylammonium (TEA+) allowed the properties of IK(f) to be analysed in isolation. 3. The activation threshold for IK(f) was normally between ‐20 and ‐10 mV and the current‐voltage relationship was linear. At positive potentials the decay of IK(f) was well fitted by a single exponential having a time constant of 20‐35 ms. At ‐70 mV recovery from inactivation was best described by a single‐exponential function with a time constant of 20‐40 ms. IK(f) was fully activatable at ‐60 mV and was fully inactivated at ‐10 mV; the half‐inactivation potential was approximately ‐25 mV. 4. Since IK(f) was reduced by raising the external concentration of K+, was blocked by Ba2+ and Cs+, and persisted in Ca2+‐free medium it is attributed to a voltage‐activated K+ conductance. The amplitude of IK(f) was unaffected either by 5 mM‐4‐aminopyridine (4‐AP) or 50 microM‐quinidine. 5. The electrical properties of IK(f) suggest that by affecting the amplitude and/or duration of the action potential IK(f) may modulate Ca2+ influx and consequently hormone release.
The effect of chronic hypoxia upon the development of respiratory chemoreflexes in the newborn kitten.
Authors: Hanson M A , Kumar P , Williams B A
Published: December 2014

1. We have studied the reflex respiratory responses to two‐breath alternations of fractional inspired oxygen (FI,O2) in normoxic (reared in room air) and chronically hypoxic kittens (born into and reared in an FI,O2 of 0.13‐0.15) on post‐natal days 1, 2‐3, 4‐8 and 9‐14. 2. Respiration was measured non‐invasively in the unanaesthetized kittens. Test runs (with alternations of FI,O2 between 0.21 and 0.14) and control runs (with an FI,O2 of 0.21) were carried out during quiet sleep. 3. The degree of alternation in tidal volume, inspiratory time, expiratory time, frequency, drive, timing and instantaneous ventilation components of the respiratory response was compared during control and test runs. 4. There was little response to control runs in either group at any post‐natal age. 5. In normoxic kittens we found no significant reflex response in any respiratory variable to test runs before day 4. However significant alternation was found in expiratory time, frequency and ventilation at days 4‐8 and in tidal volume at days 9‐14. 6. In chronically hypoxic kittens there were no significant differences between control and test runs at any of the ages studied. 7. In the normoxic group increases in the response with post‐natal age probably reflect post‐natal increases in the sensitivity of the peripheral chemoreceptors. The lack of development in the chronically hypoxic group may indicate abnormal function or delayed maturation of the peripheral chemoreceptor sensitivity to hypoxia. 8. The results suggest that the method can be used to detect developmental and pathological changes in the arterial chemoreflex.
The force‐velocity relationship at high shortening velocities in the soleus muscle of the rat.
Authors: Claflin D R , Faulkner J A
Published: December 2014

1. In intact skeletal muscle fibres, estimates of unloaded shortening velocity obtained from slack test measurements (V0) have been shown to exceed, by approximately 7%, estimates obtained from extrapolation of velocities measured during isotonic releases (Vmax). In contrast, published values for the V0 of whole soleus muscles of rats exceed Vmax by 56%. In the present study, we tested the hypothesis that this difference between whole muscles and single fibres is due to a difference in their respective force‐velocity relationships at loads less than 5% of maximum isometric tetanic force (P0). In addition, we examined, by computer simulation, the effect of inter‐fibre heterogeneity on the force‐velocity characteristics of a whole muscle. 2. The force‐velocity relationship of soleus muscles of rats was determined at low loads, in vitro at 20 degrees C, by recording force maintained during controlled shortening at constant velocities. The relationship was simulated by assigning a hyperbolic force‐velocity curve to each motor unit and summing the force contributions of individual units at each of a series of velocities. 3. When measurements from low loads were included, the force‐velocity relationship intersected the velocity axis at V0 (5.0 +/‐ 0.1 fibre lengths/s, mean +/‐ S.E.M., n = 10), not Vmax (3.1 +/‐ 0.1 fibre lengths/s). The simulated and measured force‐velocity relationships agreed at all loads, supporting the premise that the deviation from hyperbolic form responsible for the large disparity between V0 and Vmax of whole muscles is a consequence of heterogeneity in shortening velocity among fibres.
Phorbol ester effects on coupling mechanisms during cholinergic contraction of swine tracheal smooth muscle.
Authors: Baba K , Baron C B , Coburn R F
Published: December 2014

1. We studied effects of the phorbol ester, phorbol 12,13‐dibutyrate (PDB), on carbachol‐induced contractions of swine trachealis muscle. PDB (1‐10 microM) markedly inhibited 5.5 microM‐carbachol‐induced inositol phosphate synthesis allowing us to study (a) whether the membrane potential‐independent component of force (pharmacomechanical coupling component) developed in carbachol‐stimulated trachealis muscle is dependent on activation of inositol phospholipid metabolism, and (b) whether carbachol‐induced membrane depolarization and contraction are altered in muscle where second messenger signals generated by inositol phospholipid metabolism are inhibited and activation of protein kinase C (PKC) is already maximal. 2. Application of PDB (10 microM) to unstimulated trachealis muscle resulted in a small slowly developing contraction associated with a 10 m V membrane depolarization. PDB‐evoked contractions were not influenced by Na+ or Cl‐ ion substitutions, or administration of amiloride, all of which inhibited PDB‐evoked membrane depolarization. 3. Pre‐treatment with PDB had no effect on [K+]‐force, or [K+]‐membrane potential relationships, over a range of extracellular [K+] from 40 to 70 mM. Pretreatment with PDB had no effect on extracellular [Ca2+]‐force relationships during 40 mM‐K+. 4. Carbachol‐evoked contractions of muscle treated with PDB became similar to K+ contractions in regard to effects of organic Ca2+ antagonist drugs or decrease in bathing solution [Ca2+]. At low carbachol concentrations, verapamil plus PDB completely inhibited force development. With 5.5 microM‐carbachol, over 90% of total carbachol‐induced force was inhibited by verapamil, or nifedipine, plus PDB. 5. Control carbachol‐evoked contractions were associated with 20‐25 mV membrane depolarizations. In PDB‐treated muscle, carbachol‐evoked contraction occurred with a blunted depolarization, i.e. about 5 mV. 6. Force controlled by pharmacomechanical coupling mechanisms operating during maintained carbachol‐evoked contractions was inhibited by treatment with PDB. Carbachol‐induced force dependent on pharmacomechanical coupling mechanisms could be explained by signals generated via inositol phospholipid metabolism. 7. Electromechanical coupling mechanisms were augmented during carbachol in PDB‐treated muscle. This appears to be due primarily to changes in the properties or number of surface membrane voltage‐gated Ca2+ channels. 8. Data suggest an important role of PKC‐mediated phosphorylations for control of both pharmacomechanical coupling mechanisms mediated by activation of inositol phospholipid metabolism and electromechanical coupling mechanisms mediated by effects on operation of surface membrane ion channels.
Calcium‐force coupling mechanisms during vasodilator‐induced relaxation of ferret aorta.
Authors: DeFeo T T , Morgan K G
Published: December 2014

1. The effects of three vasodilators, nifedipine, hydralazine and forskolin, were determined on isometric force and intracellular ionized calcium concentration ([Ca2+]i) as indicated by aequorin in ferret aorta. Three types of contraction were studied: the intrinsic tone induced by warming from 22 to 37 degrees C; the contraction to the phorbol ester 12‐deoxyphorbol‐13‐isobutyrate‐20‐acetate (DPBA); and the contraction to potassium depolarization. 2. On warming there was no significant steady‐state change in [Ca2+], even though 5.7 +/‐ 0.7 mN of tone developed. During potassium depolarization, [Ca2+]i rose to a sustained plateau while DPBA caused no significant rise in [Ca2+]i. 3. Nifedipine and hydralazine inhibited intrinsic tone while causing an associated decrease in [Ca2+]i; but in the presence of forskolin, a similar inhibition of tone was accompanied by no significant decrease in [Ca2+]i. 4. Nifedipine and hydralazine prolonged the characteristic lag phase before force development in response to DPBA but did not cause a significant change in contraction amplitude. In contrast, forskolin caused an essentially total inhibition of the contraction. 5. During potassium depolarization, all three vasodilators caused significant decreases in [Ca2+]i coincident with decreases in steady‐state force. Calcium‐force curves were constructed by plotting the calibrated aequorin light signal against the resulting force. The control calcium‐force curve was not shifted by nifedipine or hydralazine but was significantly shifted to the right by forskolin.
Characterization of Ca2+ and K+ currents in the human Jurkat T cell line: effects of phytohaemagglutinin.
Authors: Dupuis G , Héroux J , Payet M D
Published: December 2014

1. Inward and outward currents were recorded in the human Jurkat T cell line using the whole‐cell configuration of the patch‐clamp technique. 2. The transient outward current was activated at membrane potentials positive to ‐60 mV. The activation time constant‐voltage relationship decreased from 17 ms to 2 ms for membrane potentials ranging from ‐40 to +40 mV. The inactivation phase could be fitted by a single‐exponential function and the inactivation time constant decreased from 250 ms to 150 ms for membrane potentials ranging from ‐20 to +100 mV. 3. The steady‐state inactivation‐voltage relationship showed a mid‐point potential of ‐32 +/‐ 2.6 mV, and the slope factor was 10.8 +/‐ 1.8 mv (n = 3). 4. The calcium ionophore A23187 provoked a decrease in the amplitude of the outward current, suggesting a dependence of this current on the cytosolic concentration of Ca2+. 5. The K+ outward current was blocked by tetraethylammonium (TEA, Michaelis‐Menten constant (Km), 6 mM) and by the calcium channel blockers Ni2+, Co2+, Mn2+ and Cd2+. 6. Forty per cent (n = 120) of the patched Jurkat cells displayed an inward current. In a physiological medium containing Ca2+ (2.2 mM), the inward current threshold voltage was ‐60 mV, the maximum current was observed at ‐40 mV and the zero current voltage was positive to +20 mV. At negative membrane potentials, the time required to reach 50% of the maximum amplitude was 60 ms and grew shorter with increasing depolarization, reaching a value of 5 ms at ‐5 mV. The inactivation of the inward current was very slow and the time constant varied from 1200 ms at ‐35 mV to approximately 250 ms for potentials positive to ‐10 mV. 7. The current availability had a value of one for potentials negative to ‐50 mV and zero for potentials positive to ‐15 mV. The mid‐point potential was ‐31 +/‐ 3.4 mV and the slope factor was 3.3 +/‐ 0.2 mV (n = 3). 8. The inward channels were permeable to Sr2+, but were blocked by classical Ca2+ channel inhibitors such as Co2+, Mn2+ and Ni2+. 9. Phaseolus vulgaris phytohaemagglutinin (PHA), an inducer of interleukin‐2 production in Jurkat cells, increased the inward current amplitude by 32 +/‐ 20% (n = 4). This increase was concomitant with a decrease (45 +/‐ 12%) in the amplitude of the outward current, but only when the current was carried by Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
A voltage‐dependent outward current with fast kinetics in single smooth muscle cells isolated from rabbit portal vein.
Authors: Beech D J , Bolton T B
Published: December 2014

1. Single smooth muscle cells were isolated enzymatically from the rabbit portal vein. They were voltage‐clamped at room temperature using the whole‐cell configuration of the patch‐clamp technique. 2. When cells were bathed in physiological salt solution, depolarization from a holding potential of ‐70 mV elicited a time‐dependent outward current which reached a maximum within 0.2‐0.5 s, but when a more negative holding potential was used, an additional outward current could be activated. The current (Ifo) developed rapidly, was transient and seemed to be carried by potassium ions (K+). 3. The steady‐state inactivation plot for Ifo was steeply voltage‐dependent between ‐90 and ‐60 mV, current being 50% inactivated at ‐78 mV. The activation threshold was around ‐65 mV. The activation and inactivation kinetics were fast and voltage‐dependent. When the test potential was ‐35 mV, peak current occurred after about 15 ms and the decay was complete within 250 ms. Recovery from inactivation was maximal after 1 s at ‐100 mV but was about five times slower at ‐70 mV. 4. The outward current Ifo was blocked completely by 4‐aminopyridine (5 mM) or phencyclidine (0.1 mM), but was insensitive to tetraethylammonium ions (32 mM), apamin (0.1 microM), charybdotoxin from the venom of Leiurus quinquestriatus (0.1 microM), toxin‐I from the venom of Dendroaspis polylepis (1 microM) or the putative K+ channel opener, cromakalim (10 microM). 5. The steady‐state inactivation range and activation threshold, kinetics of activation and inactivation all showed a marked dependence on the concentration of divalent cations in the bathing solution. This effect was consistent with the hypothesis that Ifo was affected by membrane surface potential. The current did not seem to be Ca2+‐activated. 6. Ifo closely resembled the A‐current which has been described previously in neurones but not in smooth muscle.
Mechanical influences on long‐lasting human muscle fatigue and delayed‐onset pain.
Authors: Jones D A , Newham D J , Torgan C
Published: December 2014

1. The influence of three mechanical factors, force, muscle length and passive lengthening, on long‐lasting changes in voluntary force generation, the force:frequency relationship and the development of tenderness has been studied in healthy human skeletal muscle. The elbow flexors were used in all studies. The effect of muscle length was also investigated in the quadriceps and adductor pollicis muscles. Eighty maximal voluntary contractions (MVCs) were performed: one contraction, lasting approximately 2 s, every 15 s. The MVC and force:frequency relationships were measured before and immediately after the exercise and, together with an assessment of tenderness, at 24 h intervals thereafter. 2. In a series of experiments designed to investigate the effects of force, eccentric (lengthening) contractions were found to cause greater fatique and delayed‐onset muscle pain than either isometric or concentric (shortening) contractions. There were, however, no substantial differences between the effects of isometric and concentric contractions. Changes in MVC took 24‐48 h to return to normal while the low‐frequency fatigue required 3‐4 days to recover. 3. Passive lengthening with a comparable number of movements over the full range had no effect on the force generation of the muscle, nor did it cause any muscle pain. 4. In the series of experiments designed to investigate the effects of length, isometric MVCs were performed at either short or long length and the muscles subsequently tested at an intermediate length. The contractions at long length resulted in greater low‐frequency fatigue and pain, despite the fact that they generated less force than those at the short length. 5. The results demonstrate that there is no simple relationship between the force generated during exercise and the development of long‐lasting muscle fatigue and pain. Furthermore, there is a length‐dependent component in the generation of low‐frequency fatigue and muscle pain.
Analysis of factors that contribute to cardiovascular changes induced in the cat by graded levels of systemic hypoxia.
Authors: Marshall J M , Metcalfe J D
Published: December 2014

1. In cats anaesthetized with Saffan, which does not block afferent activation of the brain stem defence areas, we have analysed the cardiovascular changes induced by 3 min periods of graded systemic hypoxia (fraction of O2 in inspirate, Fi,O2, 0.15, 0.12, 0.08, 0.06). 2. At light levels of Saffan anaesthesia, hypoxia (particularly Fi, O2 0.08 and 0.06) or selective stimulation of carotid chemoreceptors evoked the pattern of tachycardia, decrease in renal and mesenteric vascular conductance (RVC, MVC), but increase in femoral vascular conductance (FVC) which is characteristic of the alerting‐defence response. This supports our view that activation of the defence areas is an integral part of the response to systemic hypoxia. 3. Hypoxia also induced an increase in frequency of augmented breaths which was graded with the level of hypoxia: 0.6 min‐1 at Fi, O2 0.21 to 1.1 min‐1 at Fi, O2 0.06; in some cats each of these was accompanied by a transient fall in arterial pressure (ABP) and increase in FVC. It is proposed that these responses were all part of a reflex elicited by lung irritant receptors and facilitated by peripheral chemoreceptors. However, their low rate of occurrence and the liability of the vasodilatation suggests they do not make major contributions to the overall response. 4. The above short‐lasting responses were superimposed upon gradual changes whose magnitudes were graded with the level of hypoxia: hyperventilation, slight tachycardia, but bradycardia at Fi, O2 0.6, small increases in ABP, FVC and MVC allowing femoral and mesenteric blood flow to increase, but decreases in RVC which maintained renal blood flow constant. 5. Vagotomy had no significant effect on these changes. Further, hyperinflation of the lungs with pressures of 10 mmHg evoked the Breuer‐Hering reflex but had no noticeable cardiovascular effect. It is proposed that, in the cat, reflex tachycardia and vasodilatation elicited by lung stretch receptors play no significant part in the response to hypoxia. 6. By contrast, after pneumothorax, with ventilation and thereby arterial PCO2 (Pa, CO2) maintained constant, graded hypoxia produced graded bradycardia, decrease in MVC and RVC and no change in FVC. Taken together, these results suggest that in the spontaneously breathing cat, the response to hypoxia is dominated by the effects of hypocapnia secondary to hyperventilation, which by inhibiting peripheral and central chemoreceptor activity effectively counteracts the primary bradycardia and peripheral vasoconstriction elicited by hypoxic stimulation of peripheral chemoreceptors. 7. These proposals are compared with those drawn for other species.
Enkephalinergic inhibition in parasympathetic ganglia of the urinary bladder of the cat.
Authors: de Groat W C , Kawatani M
Published: December 2014

1. Repetitive stimulation (10‐20 Hz, 0.5‐5 s duration) of the preganglionic nerves to ganglia on the surface of the urinary bladder of the cat produced a prolonged inhibition (duration, 30‐65 s) of the postganglionic action potentials, elicited by low‐frequency stimulation (0.25‐1 Hz) of another preganglionic nerve to the same ganglion. 2. Intra‐arterial administration of naloxone, an opiate antagonist (20‐50 micrograms/kg), reduced the magnitude and duration of this heterosynaptic inhibition and also blocked the depression of ganglionic transmission elicited by the intra‐arterial administration of leucine‐enkephalin (0.1‐10 micrograms/kg). 3. Naloxone did not alter adrenergic inhibition elicited by repetitive stimulation of the hypogastric nerve or exogenous noradrenaline. Naloxone did not alter the postganglionic firing elicited by single stimuli or trains of low‐frequency (1‐3 Hz) stimuli to the preganglionic nerves. 4. Heterosynaptic inhibition was not altered by the administration of antagonists for alpha‐adrenergic (dihydroergotamine, prazosin, yohimbine), muscarinic (atropine), purinergic (theophylline) or GABAergic (picrotoxin) receptors. 5. A delta‐selective opiate receptor agonist, DSLET (D‐Ser2‐leucine‐enkephalin‐Thr), inhibited parasympathetic ganglionic transmission in low doses (mean threshold dose, 0.02 microgram/kg, I.A.), whereas a mu‐opiate receptor agonist, morphine sulphate, produced only a small depression in larger doses (mean threshold dose, 100 micrograms/kg, I.A.). Ethylketocyclazocine, which has an affinity for kappa‐receptors did not alter transmission in relatively large doses (1 mg/kg, I.A.). 6. These findings coupled with previous immunocytochemical demonstrations of leucine‐enkephalin‐like immunoreactivity in preganglionic nerve terminals in bladder ganglia suggest that opioid peptides released endogenously from preganglionic nerves are involved in delta‐receptor‐mediated inhibitory mechanisms at cholinergic synapses in bladder ganglia.
The mechanism of early contractile failure of isolated rat ventricular myocytes subjected to complete metabolic inhibition.
Authors: Lederer W J , Nichols C G , Smith G L
Published: December 2014

1. Twitch shortening of isolated rat ventricular myocytes was measured on exposure to complete metabolic blockade (2 mM‐cyanide in the presence of 10 mM‐2‐deoxyglucose). Under these conditions twitch shortening declines to undetectable levels over 1‐15 min. This ‘early’ contractile failure is followed by the development of a maintained contracture. 2. Contractures induced by caffeine (20 mM) were similar in amplitude before and after ‘early’ contractile failure. This result suggests that ‘early’ contractile failure is not due to depletion of Ca2+ from the sarcoplasmic reticulum. 3. The action potential shortened as the twitch magnitude declined during ‘early’ contractile failure, raising the possibility of a causal link. Voltage‐clamp experiments show that an enormous increase in K+ conductance (greater than 20‐fold) occurs during the period of ‘early’ contractile failure, and presumably underlies the action potential shortening. 4. If the K+ conductance changes are inhibited by replacement of intracellular K+ with N‐methyl glucosamine and inclusion of 2 mM‐tolbutamide in intra‐ and extracellular solutions, good voltage control can be achieved. Under these conditions, ‘early’ contractile failure did not occur on exposure to complete metabolic blockade and neither Ca2+ current nor the twitch were completely abolished until a maintained contracture had begun to occur. 5. Injection of ATP following ‘early’ contractile failure could partially restore the twitch and prolong the foreshortened action potential. 6. These results are consistent with the hypothesis that ‘early’ contractile failure occurring under non‐voltage‐clamped conditions is due principally to failure of activation of the Ca2+ current because of the shortening of the action potential. Although a decline in the availability of Ca2+ current also occurs, action potential shortening results mainly from increased conductance through ATP‐sensitive K+ channels which are activated by a fall of intracellular [ATP]. Contractile failure arises not because of a primary alteration, or defect, in the coupling of excitation to contraction, but because the cell membrane is effectively clamped at a potential close to the K+ equilibrium potential.