bluuebunny/crossref_metadata_2025 huggingface dataset:
Some properties of the membrane currents underlying the fertilization potential in sea urchin eggs.
Authors: David C , Halliwell J , Whitaker M
Published: December 2014

1. The ionic currents that underly the fertilization potential of sea urchin eggs were studied in Lytechinus pictus using a single‐electrode voltage clamp technique. 2. In unfertilized eggs, a transient inward current was activated at membrane potentials more positive than ‐45 mV. The maximum amplitude of the current was 0.56 +/‐ 0.35 nA (mean +/‐ S.D., n = 33) at a membrane potential of ‐35 to ‐25 mV. 3. The amplitude of this transient inward current was decreased by reducing the external concentration of calcium ions and by substituting barium or strontium ions for calcium in the external medium. Cobalt (10‐20 mM) and gadolinium (200‐500 microM) ions reduced the amplitude of this current in the presence of calcium ions. 4. A transient outward current was activated in unfertilized eggs at membrane potentials more positive than ‐10 mV. This current inactivates with a time constant of 16 ms at a membrane potential of ‐9 mV and re‐activates over a period of several seconds at a membrane potential of ‐72 mV. 5. When unfertilized eggs were treated with the calcium ionophore A23187 under voltage clamp conditions, an inward current developed. It reached a maximum 30 s after its onset and declined thereafter. By 90 s it had become constant at 10% of its peak value. 6. The inward current induced by A23187 was voltage dependent. It was maximal at ‐25 mV in the steady state. 7. When eggs were fertilized under voltage clamp conditions, the fertilization current, If, was recorded. At a holding potential of ‐50 or ‐70 mV If had the following characteristics: (a) an initial inward shoulder with a duration ranging from 12 to 30 s; (b) an inward current peak that was attained between 40 and 100 s after the onset of the shoulder current and declined over the next 60 s; (c) an outward current that appeared after the inward current had declined. 8. Current‐voltage relations obtained during If showed that the late component of the inward current was voltage dependent. It was maximal at ‐25 mV in the steady state and resembled the late component of the inward current recorded in A23187‐activated eggs. 9. These results indicate that the form of the action potential in unfertilized eggs is due to the activation of a transient inward current and an inactivating outward current. The sustained depolarization after fertilization is due to the activation of a voltage‐dependent inward current by the increase in intracellular free calcium concentration that occurs at fertilization.
Passive electrical properties and electrogenic sodium transport of cultured guinea‐pig coronary endothelial cells.
Authors: Daut J , Mehrke G , Nees S , Newman W H
Published: December 2014

1. Coronary endothelial cells were isolated from adult guinea‐pig hearts (Nees, Gerbes & Gerlach, 1981) and the electrical properties of primary cultures were studied using the tight‐seal whole‐cell recording mode of the patch clamp technique. 2. On the third or fourth day in culture whole‐cell clamp records from single coronary endothelial cells were obtained at 37 degrees C. The resting potential was ‐33 +/‐ 6 mV (n = 10). The membrane time constant determined with rectangular current pulses was 68 +/‐ 22 ms (n = 10). 3. In voltage clamp experiments, no time‐dependent membrane conductance changes were found in the range ‐80 to +40 mV. The current‐voltage relation was linear in normal physiological salt solution containing 5.4 mM‐K+. The input resistance was 1.7 +/‐ 0.4 G omega. When the external K+ concentration was increased to 116 mM the cells depolarized to about ‐3 mV and the clamp currents showed marked inward rectification. 4. Between days four and seven in culture the endothelial cells formed confluent monolayers which showed the characteristic ‘cobblestone’ morphology. The input resistance of cells in a monolayer was 8 +/‐ 3 M omega, i.e. a factor of 200 lower than that found in single cells. It was concluded that the cells in the confluent monolayer are coupled electrically by gap junctions. 5. Exposure of coronary endothelial cells to K+‐free solution for 5 min produced a depolarization of about 8 mV. Upon readmission of normal external K+ the cells transiently hyperpolarized by up to 20 mV. This transient hyperpolarization decayed with a time constant of 1.9 +/‐ 0.3 min. 6. The transient hyperpolarization could be abolished by application of 2 x 10(‐4) M‐dihydro‐ouabain (DHO). Application of DHO in the steady state produced a depolarization of 8 +/‐ 1 mV. From these findings it was concluded that coronary endothelial cells possess an electrogenic sodium pump which contributes about ‐8 mV to the resting potential. 7. From the passive electrical properties of single cells and the morphological data available it was calculated that endothelium in situ may have a large electrical space constant, probably between 250 and 550 microns. 8. The functional implications of the large space constant of the endothelial monolayer are discussed. It is suggested that intra‐endothelial conduction of electrical signals from capillaries to the resistance vessels may be involved in the local regulation of blood flow in the intact heart.
The control of glomerular filtration rate and renal blood flow in chronically volume‐expanded rats.
Authors: Davis J M , Häberle D A , Kawata T
Published: December 2014

1. Chronic volume expansion by dietary salt loading practically abolishes tubuloglomerular feed‐back (TGF) by means of a humoral inhibitor in tubular fluid. Elimination of the vasoconstrictor influence of feed‐back does not, however, increase glomerular filtration rate (GFR) and renal blood flow (RBF), implying that chronic salt loading induces additional preglomerular vasoconstriction. This being so, the feed‐back response which, although absent in free‐flowing nephrons, can still be elicited by loop of Henle perfusion with Ringer solution, should be essentially normal, except that nephron GFR at any loop perfusion rate should be lower than in controls. Persistence of RBF, GFR and nephron GFR autoregulation would imply that autoregulation is achieved by a preglomerular resistance control system independent of feed‐back. 2. These hypotheses were tested by clearance and micropuncture experiments in rats chronically fed a diet containing 40 g NaCl (kg food)‐1. 3. RBF and GFR autoregulation indeed persisted, the former down to 90 mmHg compared with 105 mmHg in controls. In controls, nephron GFR measured distally was autoregulated down to 90 mmHg whereas that measured proximally was autoregulated only above 105 mmHg. In high‐salt rats nephron GFR from both sites was autoregulated to 90 mmHg. 4. Loop of Henle perfusion with homologous tubular fluid in high‐salt rats confirmed attenuation of feed‐back. Loop perfusion with Ringer solution yielded a response comparable to that in controls (maximal reduction of nephron GFR to 57%, compared with 56% in controls). Absolute nephron GFR at any loop perfusion rate was lower in high‐salt rats than in controls. 5. These observations confirm the initial hypotheses. Considering feed‐back and autoregulation as independent, preglomerular resistance control mechanisms, together with elementary haemodynamic considerations, allows formulation of a renal haemodynamics model whose quantitative predictions regarding characteristics of RBF, GFR and feed‐back control are remarkably consistent with the literature.
Effect of ionic composition of milk on transepithelial potential in the goat mammary gland.
Authors: Blatchford D R , Peaker M
Published: December 2014

1. A method is described for altering the ionic composition of the alveolar (residual) milk in the goat mammary gland. Transepithelial (blood‐milk) potential difference (PD) was recorded before and after composition was changed. 2. When [Na+] and [K+] were varied while [Na+ + K+] and [Cl‐] were maintained constant, there were no significant changes in PD. 3. When [Na+] was varied, with [K+] and [Cl‐] constant, there was a linear relation between PD and log [Na+], with a change of 18 mV per tenfold change in concentration. 4. When [K+] was varied, with [Na+] and [Cl‐] constant, there was a linear relation between PD and log [K+], with a change of 24 mV per tenfold change. 5. In view of the lack of discrimination between Na+ and K+ in the first experiment, the sum of [Na+] and [K+] was considered. In the experiments in which [Na+] or [K+] were varied, there was a change of 37 and 38 mV, respectively, per tenfold change in [Na+ + K+]. The quantitative effects on PD of changing [Na+] or [K+] when expressed as changes in [Na+ + K+] were not significantly different. 6. When [Cl‐] was varied, with [Na+] and [K+] constant, there was a linear relation between PD and log [Cl‐], with a change of 22 mV per tenfold change. 7. The results are discussed in relation to the types of ion channel that might be present in the apical membrane of the secretory cell and in relation to hypotheses on the mechanisms of ion transport in the mammary gland.(ABSTRACT TRUNCATED AT 250 WORDS)
Stimulation of afferent fibres of the guinea‐pig ureter evokes potentials in inferior mesenteric ganglion neurones.
Authors: Amann R , Dray A , Hankins M W
Published: December 2014

1. Intracellular recordings were made from neurones of the guinea‐pig inferior mesenteric ganglion (IMG) maintained in vitro with both ureters and major nerve trunks attached. Afferent fibres in the ureteric nerve were activated by electrical, chemical and mechanical stimuli. 2. Repetitive stimulation of a ureteric nerve branch evoked a non‐cholinergic, synaptic slow excitatory potential (slow EPSP) in 48% of neurons. The amplitude of the slow EPSP was dependent on membrane potential and was decreased by membrane depolarization and increased by hyperpolarization. 3. The slow EPSP was attenuated or abolished by capsaicin (1 microM), which itself depolarized IMG neurones. Substance P (2 microM) or neurokinin A (2 microM) also depolarized IMG neurones and in the presence of these tachykinins the slow EPSP was attenuated or abolished. 4. Distension of the ureter evoked a non‐cholinergic slow depolarization in 45% of IMG neurones which was abolished by tetrodotoxin (1 microM) and by capsaicin (1 microM). 5. Chemical stimulation of ureteric afferent nerve terminals by intralumenal perfusions of the ureter with capsaicin (1 microM) produced a slow depolarization in the IMG which was prevented by blocking nerve conduction with TTX. 6. These data demonstrate that electrical stimulation of ureteric afferent fibres produces a non‐cholinergic slow EPSP in the IMG. Primary afferent (capsaicin‐sensitive) C fibres are also activated by distension of the ureter and evoke a slow depolarization in the IMG. The synaptic mediator of these events is likely to be tachykinin(s) released from capsaicin‐sensitive C fibres. These fibres may be mechanosensory and/or nociceptive.
Chloride ion transport into pig jejunal brush‐border membrane vesicles.
Authors: Forsyth G W , Gabriel S E
Published: December 2014

1. This study was carried out to determine the types and activities of carrier proteins which transport the chloride ion in pig jejunal brush‐border membranes, with an emphasis on studying the properties of chloride conductance activity in vesicles prepared from these membranes. 2. Sodium‐chloride co‐transport activity was not detected in this tissue. A sodium‐proton antiport with typical amiloride sensitivity was present. An anion exchanger linking chloride to hydroxyl or bicarbonate ions was also found in the pig jejunal brush‐border membrane vesicles. 3. Chloride conductance activity in this system was specifically dependent on the buffering agents used for vesicle preparation. Conductance activity could not be demonstrated in vesicles prepared in imidazolium acetate or in HEPES‐Tris buffers. HEPES‐tetramethylammonium buffering of vesicles in the chloride uptake system produced a significant conductance response to a potassium gradient plus valinomycin. 4. Chloride conductance showed saturable kinetics with respect to substrate concentration, with a Michaelis‐Menten constant (Km) of approximately 116 mM and a maximum velocity (Vmax) of 132 nmol (mg protein)‐1 min‐1. 5. Preliminary screening of potential inhibitors of chloride conductance showed only minimal inhibitor effects of SITS (4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐sulphonic acid), anthracene‐9‐carboxylate, N‐phenylanthranilate and piretanide. 6. The conductance activity in pig jejunal vesicles appears to have stringent buffer requirements, and to be relatively insensitive to the effects of reported conductance inhibitors.
Brain fluid calcium concentration and response to acute hypercalcaemia during development in the rat.
Authors: Jones H C , Keep R F
Published: December 2014

1. In vivo measurements of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid (ISF) ionic Ca2+ concentrations ([Ca2+]) have been made in anaesthetized rats aged between 19 days gestation and adult using calcium‐selective microelectrodes. Total calcium concentration ([ Ca]) has also been determined in plasma and CSF samples by atomic absorption spectrometry. 2. Under control conditions, plasma, CSF and ISF [Ca2+] showed a small, but significant, decrease with age. Plasma and CSF, but not ISF, showed a transient hypocalcaemia at birth. After birth there were no significant differences between plasma, CSF and ISF [Ca2+], except in adult rats where CSF [Ca2+] was significantly lower than plasma [Ca2+]. The age‐related changes in CSF and ISF [Ca2+] were small and it is uncertain as to whether they may have any functional significance. 3. Under control conditions, plasma and CSF [Ca] also declined with age. The fall in plasma [Ca] paralleled the changes in plasma [Ca2+]. The decrease in CSF [Ca] was steeper than that in [Ca2+] and indicated a higher proportion of protein‐bound or complexed calcium in the CSF of young when compared to old rats. 4. Acute plasma hypercalcaemia was induced by intramuscular injections of calcium gluconate and consequent changes in CSF or ISF [Ca2+] were monitored in vivo. There was very weak regulation of CSF and ISF [Ca2+] at 21 days gestation, which may reflect placental control over fetal plasma calcium. Soon after birth there was good regulation in both ISF and CSF [Ca2+]. CSF [Ca] was also measured during hypercalcaemia in samples from post‐natal rats and there was similar regulation to that in CSF [Ca2+]. 5. It is concluded that under control conditions, during rat development, CSF and ISF [Ca2+] closely follow changes in plasma [Ca2+], but that soon after birth homeostatic mechanisms develop to prevent large fluctuations in brain fluid calcium.
Electrical stimulation resembling normal motor‐unit activity: effects on denervated fast and slow rat muscles.
Authors: Eken T , Gundersen K
Published: December 2014

1. The slow‐twitch soleus muscle and the fast‐twitch extensor digitorum longus muscle (EDL) were denervated and stimulated directly with implanted electrodes for 33‐82 days. Four different stimulation patterns were used in order to mimic important characteristics of the natural motor‐unit activity in these muscles. In addition, to compare the effects of direct stimulation to other experimental models, some EDLs were stimulated through the nerve or cross‐innervated by soleus axons. 2. After 33‐82 days of stimulation the contractile properties were measured under isometric and isotonic conditions. 3. ‘Native’ stimulation patterns could maintain normal contractile speed in both EDL and soleus. In the EDL, normal isotonic shortening velocity was maintained only by a stimulation pattern consisting of very brief trains with an initial short interspike interval (doublet), and not by the other ‘native’ high‐frequency patterns. 4. The contractile properties of both EDL and soleus muscles receiving a ‘foreign’ stimulation pattern were transformed in the direction of the muscle normally receiving that type of activity. The transformations were not complete, and soleus and EDL muscles stimulated with the same stimulation pattern remained different. This suggests that adult muscle fibres in rat EDL and soleus are irreversibly differentiated into different fibre types earlier in development. 5. The three high‐frequency stimulation patterns used differed in their ability to change or maintain various contractile properties in the soleus and the EDL. The results indicate that the following qualities of a stimulation pattern might be of importance for the control of contractile properties: instantaneous frequency, total amount of stimulation, train length, interval between trains and presence of an initial doublet. 6. With the exception of the EDL shortening velocity, changes in contractile speed induced by a ‘foreign’ stimulation pattern were quantitatively similar to the effects of cross‐innervation both in the EDL and the soleus. We thus suggest that the change in activity pattern is the mechanism behind most of the changes induced by cross‐innervation.
Stiffness changes in frog skeletal muscle during contraction recorded using ultrasonic waves.
Authors: Hatta I , Sugi H , Tamura Y
Published: December 2014

1. A technique has been developed with which the stiffness changes in frog skeletal muscle can be continuously recorded by measuring the propagation velocity of ultrasonic waves (3‐7 MHz) with negligibly small perturbations to the contractile system. 2. The resting muscle stiffness was 2.256 +/‐ 0.002 x 10(9) N/m2 (S.D.) at 1‐2 degrees C (n = 10) and 2.480 +/‐ 0.007 x 10(9) N/m2 at 19‐20 degrees C (n = 12) in the longitudinal direction, and 2.223 +/‐ 0.008 x 10(9) N/m2 at 1‐2 degrees C (n = 8) and 2.437 +/‐ 0.007 x 10(9) N/m2 at 19‐20 degrees C (n = 9) in the transverse direction. 3. The resting muscle stiffness measured with ultrasonic waves was virtually insensitive to the resting force development, i.e. the extension of the parallel elastic component. 4. The longitudinal muscle stiffness increased during isometric contraction at a rate faster than the force development. The amount of increase of the longitudinal stiffness in an isometric tetanus at 2.2 microns sarcomere length was 2.4 +/‐ 0.1 x 10(7) N/m2 at 1‐2 degrees C (n = 10) and 6.5 +/‐ 1.3 x 10(7) N/m2 at 19‐20 degrees C (n = 12). 5. On the other hand, the transverse muscle stiffness decreased during isometric contraction at a rate faster than the force development. The amount of decrease of the transverse stiffness in an isometric tetanus at 2.2 microns sarcomere length was 5.6 +/‐ 0.1 x 10(7) N/m2 at 1‐2 degrees C (n = 8) and 6.4 +/‐ 0.3 x 10(7) N/m2 at 19‐20 degrees C (n = 9). 6. The amount of both the longitudinal and the transverse stiffness changes during an isometric tetanus decreased linearly with increasing sarcomere length, indicating that the stiffness changes during contraction reflect the formation of cross‐links between the myofilaments. 7. Both the longitudinal and the transverse stiffness increased when resting muscle was put into rigor state. The rigor muscle stiffness was insensitive to small stretches, i.e. the strain of the rigor cross‐links. 8. These results are discussed in connection with the behaviour of cross‐bridges during isometric contraction and in rigor.
Studies of the sodium‐calcium exchanger in bull‐frog atrial myocytes.
Authors: Campbell D L , Giles W R , Robinson K , Shibata E F
Published: December 2014

1. Experimental measurements and computer simulations have been used in attempts to identify an exchanger current (Iex) generated by an electrogenic Na+‐Ca2+ exchanger in single cells from bull‐frog atrium. 2. Voltage clamp measurements of an inward 'slow tail' current observed upon repolarization after depolarizing clamp pulses that elicit net inward Ca2+ currents (ICa) (see Campbell, Giles & Shibata, 1988c), show that these slow tails have a cationic dependence different from ICa. Slow tails are large and prominent in normal [Na+]o solutions containing either Ca2+ or Sr2+, but they are markedly reduced or absent in Ba2+, Ca2+‐free, and Na+‐free solutions. 3. Kinetic measurements on the slow tails show that they are not generated by deactivation of ICa, and suggest that they may be due to activation of Iex at negative potentials (‐70 to ‐100 mV). 4. Computer simulations of the influx, buffering, and extrusion of Ca2+ provide further indirect evidence that the slow tails correspond to Iex. In addition, these calculations give insights into one plausible mechanism of Ca2+ homeostasis in frog atrium. When the Na+‐Ca2+ exchanger formalism of Mullins (1979, 1981), as modified by DiFrancesco & Nobel (1985), is combined with equations for intracellular Ca2+ buffering by myoplasmic proteins (cf. Robertson, Johnson & Potter, 1981), slow inward tails are produced which are qualitatively similar to those recorded experimentally. 5. Comparisons of the size and time course of ICa with those of Iex suggest that Iex does not generate a physiologically significant current (or membrane potential change) during the plateau of the action potential. However, at potentials near the resting potential the inward current due to Iex may be significant. 6. Our theoretical results suggest that in the intact single atrial cell myoplasmic Ca2+‐binding proteins (e.g. calmodulin and troponin) could be physiologically important modulators of the amplitude, polarity and kinetics of Iex. Hence, the specificity, capacity and kinetics of intracellular Ca2+ binding are essential components of any quantitative treatment of Iex in excitable tissue.
Repolarization current in embryonic chick atrial heart cells.
Authors: Clay J R , Hill C E , Roitman D , Shrier A
Published: December 2014

1. We have measured the delayed rectifier potassium current, IK, with the whole‐cell patch‐clamp technique from single cultured cells from the atria of 6‐ to 11‐day‐old chick embryonic hearts. 2. The IK component was activated with depolarizing voltage‐clamp steps positive to ‐30 mV (holding potential in the ‐60 to ‐40 mV range). Maximum activation of the IK conductance occurred at +25 mV, based on deactivation, or tail current amplitudes upon return to the holding potential. Activation and tail current kinetics could both be described by single‐exponential functions of time. 3. The IK kinetics were voltage dependent, with a maximum time constant, tau n, of approximately 2 s at V = ‐20 mV. 4. The IK reversal potential measurements suggest that this current is carried predominantly by potassium ions. 5. The IK results from single cells, or clusters of two or three cells, were comparable to our recent measurements of IK (IX2) in heart cell aggregates (Shrier & Clay, 1986). However, we did not obtain clear evidence in single cells for the IX1 repolarization current, in contrast to the aggregate results. 6. Computer simulations based on our IK measurements demonstrate that this component is sufficient to initiate repolarization of the action potential in single cells. However, it is not sufficient to reproduce the latter phase of repolarization for potentials negative to ‐30 mV. Addition of a relatively small IX1 component (2% in absolute terms compared to the aggregate work) is sufficient to account for this part of the action potential.
Cross‐bridge behaviour in skinned smooth muscle of the guinea‐pig taenia coli at altered ionic strength.
Authors: Arheden H , Arner A , Hellstrand P
Published: December 2014

1. The effects of varied levels (25‐300 mM) of ionic strength on mechanical properties and ATP hydrolysis rate of chemically skinned guinea‐pig taenia coli fibres were investigated. 2. The tension development following activation by calcium (pCa 4.8), and relaxation following removal of calcium (pCa 9), were slower in 25 mM compared to 150 mM ionic strength. In fibres activated by thiophosphorylation of myosin light chains, by exposure to ATP‐gamma‐S, the tension development was rapid and independent of ionic strength. 3. The maximal shortening velocity (Vmax) was obtained from force‐velocity relations determined by the quick‐release method. The rate of ATP hydrolysis (JATP) was determined by measurement of pyruvate released from phosphoenolpyruvate (PEP). In order to obtain maximal Vmax and JATP at a Mg‐ATP concentration of 1 mM, an ATP regenerating system was required. In thiophosphorylated fibres 2 mM‐phosphocreatine (PCr) or 3.2 mM‐PEP were adequate for maximal Vmax and JATP respectively. In calcium‐activated fibres 5 mM‐PCr was required for maximal Vmax. 4. The isometric force of thiophosphorylated fibres showed a biphasic dependence on ionic strength with a maximum at 90 mM. Vmax was essentially unchanged between 50 and 200 mM ionic strength. At 25 mM ionic strength, isometric force and Vmax were decreased by, respectively, about 15 and 25%. At 250 mM ionic strength, isometric force and Vmax were decreased by, respectively, 47 and 33%. 5. Vmax decreased with decreasing [Mg‐ATP]. At [Mg‐ATP] less than 0.1 mM there was no difference in Vmax between 35 and 150 mM ionic strength. At 250 mM ionic strength Vmax was lower than that at 150 mM at all [Mg‐ATP]. 6. JATP during contraction in thiophosphorylated fibres at 35, 150 and 250 mM ionic strength was respectively, 0.62, 0.98 and 0.93 mumol g‐1 min‐1. The energetic tension cost (JATP/force) increased with ionic strength. 7. The force response to a quick stretch was investigated in the relaxed, contracted and rigor states at 25, 150 and 250 mM ionic strength. Stiffness in the relaxed state increased with speed of stretch and was higher the lower the ionic strength. In the contracted and rigor states, stiffness was also affected by ionic strength, but the relative effect in the contracted state was small.(ABSTRACT TRUNCATED AT 400 WORDS)
Amiloride blocks the mechano‐electrical transduction channel of hair cells of the chick.
Authors: Jørgensen F , Ohmori H
Published: December 2014

1. Effects of amiloride, applied extracellularly, on mechano‐electrical transduction (MET) currents were investigated in dissociated hair cells of a chick with a whole‐cell patch‐electrode voltage clamp technique. Amiloride blocked the MET channel. The blocking was reversible and was both dose and voltage dependent and specific to the MET channel. The voltage‐dependent Ca2+ channel of the basolateral membrane was not affected within the concentration range studied (up to 0.7 mM). 2. The limiting conductance of the MET at large negative membrane potentials decreased with increasing amiloride concentration. A dose‐response relationship of the relative MET conductance (defined as the ratio of the MET channel conductance in the presence of amiloride to that without) at membrane potentials more negative than ‐50 mV had a Hill coefficient of 1, and a dissociation constant (KD) of 5 x 10(‐5) M. 3. When amiloride was applied, the MET conductance increased as the membrane was depolarized, and the limiting value at positive membrane potentials was close to that of the control. The relationship between the relative MET conductance and the membrane potential was S‐shaped. The conductance vs. voltage relationship was shifted in a positive direction along the voltage axis as the amiloride concentration was increased. 4. The blocking effect of amiloride on the MET channel was apparently independent of the mechanical gating of the channel. The voltage‐independent block at or near the resting membrane potential and a voltage‐dependent lifting of the block at depolarized membrane potentials could be explained quantitatively by a kinetic model which postulates one blocked state and two open states which have different amiloride affinities.
Inhibition of the calcium channel by intracellular protons in single ventricular myocytes of the guinea‐pig.
Authors: Kaibara M , Kameyama M
Published: December 2014

1. The inhibitory effects of intracellular protons (Hi+) on the L‐type Ca2+ channel activity were investigated in single ventricular myocytes of guinea‐pigs by using the patch‐clamp method in the open‐cell‐attached patch configuration, where ‘run down’ of the channel was partially prevented. 2. Hi+ reduced the unitary Ba2+ current of the Ca2+ channel by 10‐20% without changing the maximum slope conductance. 3. Hi+ did not alter the number of channels in patches containing one or two channels. 4. Hi+ markedly reduced the mean current normalized by the unitary current, which gave the open‐state probability multiplied by the number of channels in the patch. The dose‐response curve between Hi+ and the open‐state probability indicated half‐maximum inhibition at pHi 6.6 and an apparent Hill coefficient of 1. 5. Hi+ shifted both the steady‐state activation and inactivation curves in a negative direction by 10‐15 mV, and the effects were reversible. 6. Hi+ did not affect the fast open‐closed kinetics represented by the C‐C‐O scheme, apart from increasing the slow time constant of the closed time. 7. Hi+ increased the percentage of blank sweeps and reduced that of non‐blank sweeps resulting in a decreased probability of channel opening. 8. Photo‐oxidation with Rose Bengal abolished the reducing effect of Hi+ on the open‐state probability (Po) in two out of ten experiments, suggesting the possible involvement of histidine residues in the Hi+ effect. 9. The above results indicate that Hi+ inhibits the Ba2+ current mainly by affecting the slow gating mechanism of the channel.
Contractile properties of skeletal muscles from young, adult and aged mice.
Authors: Brooks S V , Faulkner J A
Published: December 2014

1. Comparisons were made in vitro at 25 degrees C among soleus and extensor digitorum longus (EDL) muscles from young (2‐3 months), adult (9‐10 months), and aged (26‐27 months) male mice. We tested the hypotheses that, compared with soleus and EDL muscles of young and adult mice, those from aged mice develop decreased maximum tetanic force (P0, mN) and specific P0 (N/cm2), and that no significant differences occur for contraction time, half‐relaxation time, or force‐velocity relationship. 2. For the aged mice, the P0 of the soleus muscles and EDL muscles were 78 and 73% respectively of the values for adult mice. The specific P0 of EDL muscles of aged mice was 78% of the value of 23 N/cm2 obtained for young and adult mice. For soleus muscles, the specific P0 of 21 N/cm2 did not change with age. 3. Compared to values for young and adult mice, the contraction and half‐relaxation times of soleus muscles from aged mice were increased, but the overall force‐velocity relationships of soleus and EDL muscles did not change. The pooled values for the maximum velocity of unloaded shortening extrapolated from the force‐velocity relationship of soleus and EDL muscles were 4.6 and 10.1 fibre lengths/s, respectively. 4. The decrease in the specific P0 of the EDL muscle with ageing must result from either a decrease in the number of cross‐bridges in the driving stroke or a decrease in the force developed by each cross‐bridge.
Long‐lasting modification of the synaptic properties of rat CA3 hippocampal neurones induced by kainic acid.
Authors: Ben‐Ari Y , Gho M
Published: December 2014

1. The action of a short bath application of kainic acid (KA, 200‐250 nM, 3‐5 min) on the CA3 region of rat hippocampal slices has been studied with intracellular and extracellular recording techniques. 2. KA evoked bursts which persisted for 10‐15 min. In addition, after KA, electrical stimulation of various inputs to CA3 which elicited an EPSP‐IPSP sequence in control conditions evoked an EPSP followed by a burst. This evoked response persisted for several hours after removal of KA suggesting the occurrence of a long‐lasting modification of the synaptic properties of CA3 neurones. 3. Intracellular recordings showed the spontaneous and evoked bursts to consist of five to ten action potentials riding on a depolarizing shift 10‐25 mV in amplitude and 40‐100 ms in duration. Both spontaneous and evoked bursts were followed by a long‐lasting hyperpolarization 15‐25 mV in amplitude and 1‐1.5 s in duration. 4. We propose that both spontaneous and evoked synchronized bursts are generated by a polysynaptic network since: (a) intracellularly recorded bursts were synchronized with the bursts in extracellular field recording; (b) bursts disappeared when synaptic transmission or Na+ action potential were blocked by cobalt (1 mM) or TTX (1 microM) respectively; (c) bursts were suppressed by elevated divalent cation concentration; (d) burst occurrence was independent of the membrane potential of the cell; (e) the depolarization shift that underlies the bursts was a linear function of the membrane potential and reversed in polarity at 0 mV. In addition, the evoked bursts were all‐or‐none events with a variable latency. 5. Laminar profile analysis of the spontaneous and evoked bursts suggests that they were generated by synapses located on the distal apical segments of the dendrites of CA3 pyramidal cells. 7. The persistence of the evoked bursts was neither due to a persistent change in cell excitability nor to a long‐lasting reduction in GABAergic synaptic inhibition. 8. Bath application of a high concentration of potassium (7 mM) also induced spontaneous and evoked bursts; the latter also persisted several hours after return to control medium. 9. The N‐methyl‐D‐aspartate (NMDA) antagonist, D‐APV (D(‐)‐2‐amino‐5‐phosphonovaleric acid) (30 microM), did not block the spontaneous discharges induced by KA or high potassium, but prevented the long‐lasting effects on the synaptic responses.(ABSTRACT TRUNCATED AT 400 WORDS)
Adrenergic and opioidergic modulation of a spinal reflex in the decerebrated rabbit.
Authors: Clarke R W , Ford T W , Taylor J S
Published: December 2014

1. In the decerebrated and spinalized rabbit, electrical stimulation of the sural nerve evokes a short‐latency reflex in the ipsilateral ankle extensor gastrocnemius medialis (GM) which is tonically suppressed by endogenous opioids. In the present study we have investigated the inhibitory influences affecting this reflex in non‐spinalized, decerebrated rabbits. 2. In non‐spinalized rabbits, the thresholds and latencies of the sural‐GM reflex were significantly higher than in spinalized preparations. The opioid antagonist naloxone and the alpha‐adrenoceptor antagonist idazoxan potentiated the reflex in both preparations. Naloxone was significantly more effective in spinalized rabbits whereas idazoxan had a much larger effect in non‐spinalized animals. 3. When the spinal cord was sectioned in the presence of naloxone alone, the GM reflex always increased in size. An ipsilateral hemisection of the cord was as effective as total section in this respect. When the section was performed in the presence of idazoxan and naloxone, the response usually decreased in size. 4. The alpha 2‐adrenoceptor agonist clonidine depressed the reflex in spinalized rabbits, an action that was reversed by idazoxan but not by naloxone. 5. These data show that in the decerebrated, non‐spinalized rabbit, the sural‐GM reflex is tonically suppressed by endogenous opioids, presumably acting at the segmental level, and by an ipsilateral descending pathway which involves an alpha‐adrenoceptor‐mediated synapse. Activity in this descending pathway masks the facilitatory effects of opioid antagonists on spinal reflexes in this preparation.
On the long‐latency reflex responses of the human flexor digitorum profundus.
Authors: Matthews P B , Miles T S
Published: December 2014

1. Electromyography (surface and intramuscular) has been used to study the reflex responses of the human flexor digitorum profundus (FDP) to angular rotation of the distal interphalangeal joint of the 4th finger. This has been done with the hand in three separate positions which, owing to the arrangement of the various tendons, allow the movement to be transmitted to (a) both the flexor and extensor muscles, (b) FDP alone (extensors disengaged) and (c) neither flexor nor extensor muscles (all muscles disengaged, but cutaneous and joint receptors still potentially activated). The stimuli were applied while the subject was voluntarily contracting FDP to produce a constant level of EMG activity; this remained possible when the muscle was disengaged from the joint. 2. With all muscles connected, FDP behaved similarly to the analogous long flexor of the thumb. ‘Stretch’ elicited a prolonged complex response starting with a short‐latency component corresponding to the tendon jerk. Unloading of the contracting muscle caused a pronounced reduction of its on‐going EMG activity. The latency of this latter effect was approximately 20 ms greater than that of the initial stretch‐evoked response, thereby demonstrating that it was not due to a disfacilitation via the short‐latency pathway (on reduction of the tonic spindle afferent firing from FDP as it shortened). 3. With all muscles disengaged, movement of the joint in either direction evoked simply a weak, variable excitatory response, with a latency somewhat greater than that of the normal unloading response. This was attributed to the activation of cutaneous and/or joint receptors. The effectiveness of the disengagement of the flexor was demonstrated by the abolition of its normal stretch‐evoked short‐latency response. 4. With the flexor engaged and the extensors disengaged both stretch and release evoked their normal types of response. In control experiments, surface EMG recordings from the interosseus muscles confirmed that the procedure used for extensor disconnection was effective. These findings exclude the possibility that the reduction of EMG activity of the unloading response of FDP might be attributable to an inhibition evoked by the concomitant stretch of its antagonists. 5. The long‐latency unloading response (whether with the extensors engaged or disengaged) remained when the sensory receptors in the finger itself were inactivated, confirming that these were not responsible.(ABSTRACT TRUNCATED AT 400 WORDS)
Three components of the calcium current in cultured glomerulosa cells from rat adrenal gland.
Authors: Durroux T , Gallo‐Payet N , Payet M D
Published: December 2014

1. Ca2+ channels were studied in cultured glomerulosa cells from the rat adrenal gland. The whole‐cell configuration of the patch‐clamp technique was used. Cs+‐filled pipettes were used in order to block K+ channels. 2. Three Ca2+ components were found, namely, T, L and N, according to the nomenclature proposed by Nowycky, Fox & Tsien (1985). The T‐component was a fast transient component activated in the range ‐60 to ‐40 mV; the L‐component did not inactivate for a sustained depolarization and activated at voltages around ‐30 mV; the third component, the N‐component, was transient and was activated at voltages close to ‐20 mV. 3. A statistical analysis made on seventy‐one experiments showed that the L‐component was the most frequent (65% of the experiments), followed by the T‐ and finally the N‐ components (59 and 29% of the experiments, respectively). 4. The substitution of Ba2+ ions for Ca2+ ions greatly enhanced the L‐component's amplitude (iBa/iCa = 4) while the N‐component was unaffected and the T‐component was reduced (iBa/iCa = 0.4). 5. A comparison of the voltage‐dependent steady‐state inactivation of the three components showed that the T‐component was inactivated at ‐60 mV while the inactivation of the L‐ and N‐components was complete at ‐25 and 0 mV, respectively. 6. A run‐down effect was detected in some cells. The time stability of the L‐component was lower than that of the T‐component. The N‐component seemed to be insensitive for at least 1 h. The results for the L‐ and T‐components were obtained in cells which presented no run‐down of the current or only a weak one. 7. Cd2+ ions (5 x 10(‐5)M) completely blocked the long‐lasting component (L‐component) and slightly decreased the T‐component. 8. Bay K 8644, a dihydropyridine agonist, enhanced the L‐component at a concentration of 2.5 microM but decreased it for a higher concentration (5 microM). The T‐component was decreased in a reversible way by 1 microM‐Bay K 8644. Nifedipine, a well‐known antagonist, blocked completely the L‐component. This effect was reversed by the addition of Bay K 8644 to the perfusion medium. The T‐component was also blocked by nifedipine, a result which is in keeping with the fact that Bay K 8644 has a weak effect on this current.
Calcium currents in single isolated smooth muscle cells from the rabbit ear artery in normal‐calcium and high‐barium solutions.
Authors: Aaronson P I , Bolton T B , Lang R J , MacKenzie I
Published: December 2014

1. Ca2+ inward current was studied using the whole‐cell patch clamp technique in single smooth muscle cells enzymatically isolated from the rabbit ear artery. Currents were studied in salt solutions containing either normal (1.5 mM) Ca2+ or high (110 mM) Ba2+. Outward currents were minimized by using a high‐Na+ intracellular solution containing 10 mM‐TEA. 2. In normal‐Ca2+ solution, the threshold at which inward current could be evoked was ‐60 mV at a holding potential of ‐80 mV and ‐48 mV at a holding potential of ‐60 mV. At both holding potentials, the current showed little inactivation over 500 ms near threshold, and inactivated substantially but incompletely with larger depolarizations. In high‐Ba2+ solution where currents were 5‐10 times larger, current threshold, maximal peak amplitude and apparent reversal potential were shifted in a positive direction along the voltage axis. 3. Inward current in normal‐Ca2+ solution was only fully available negative to ‐90 mV, was half‐inactivated near ‐47 mV and was about 90% inactivated at ‐10 mV. A component of non‐inactivating current was, however, present in both normal‐Ca2+ and high‐Ba2+ solutions even after conditioning pulses of 5 s duration to +30 mV. The inactivation‐potential relationship was shifted in a positive direction in high‐Ba2+ solution, and its position showed considerable variation between cells. 4. The inward current from a holding potential of ‐70 mV was reduced in normal‐Ca2+ solution by about 50% by nifedipine (0.1 microM) in some cells at all test potentials, although at more‐negative test potentials peak current was unaffected in some cells even at 10 microM. In some cells when the holding potential was ‐90 mV, the peak current amplitude was increased markedly by 10 microM‐nifedipine. In high‐Ba2+ solution, from negative holding potentials (‐70 to ‐80 mV), nifedipine augmented peak current at test potentials negative to ‐10 mV and shifted the current threshold in a negative direction; current at potentials positive of ‐10 mV was reduced. Both effects were concentration dependent. The stimulatory effect of nifedipine was abolished and its inhibitory effect was enhanced when less‐negative holding potentials were employed. Bay K 8644 (0.1 or 1 microM) approximately doubled current amplitude in normal‐Ca2+ solution at a holding potential of ‐60 or ‐70 mV, and shifted maximal peak and threshold current in a negative direction. 5. Holding at more‐negative potentials made available a component of current which activated and inactivated at more‐negative potentials especially in high‐Ba2+ solution.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for reduced Cl‐ and increased Na+ permeability in cystic fibrosis human primary cell cultures.
Authors: Boucher R C , Cotton C U , Gatzy J T , Knowles M R , Yankaskas J R
Published: December 2014

1. Employing a primary cell culture system and intracellular microelectrodes, we quantitated and compared the Na+ and Cl‐ pathways in apical membranes of normal and cystic fibrosis (CF) human airway epithelia. 2. Like the transepithelial difference (PD) in situ, the PD of CF epithelia in culture (‐27 +/‐ 4 mV, mean +/‐ S.E.M.; n = 28) exceeded the PD of normal epithelia (‐10 +/‐ 1 mV; n = 22). The raised PD principally reflected an increase in the rate of active transport (equivalent short circuit, Ieq) for CF epithelia (61 +/‐ 9 microA cm‐2) as compared with normal epithelia (23 +/‐ 3 microA cm‐2). No significant differences in transepithelial resistance were detected. 3. As indicated by ion replacement studies (gluconate for Cl‐), the apical membrane of normal cells exhibits an apical membrane Cl‐ conductance (GCl) that can be activated by isoprenaline. CF cells do not exhibit an apical membrane GCl, nor can a GCl be activated by isoprenaline. 4. CF cells exhibited a larger amiloride‐sensitive Ieq and amiloride‐sensitive apical membrane conductance (GNa) than normal cells. Further, the amiloride‐sensitive Ieq was increased by isoprenaline in CF but not normal airway epithelia. 5. Equivalent circuit analysis yielded evidence for a more positive electromotive force (EMF) across the apical membrane and a more negative EMF across the basolateral membrane of CF cells as compared with normal cells. Baseline resistances of the apical (Ra) and basolateral (Rb) membranes did not differ for normal and CF cells. 6. Estimates of the resistance of the paracellular path to ion flow (Rs) by equivalent circuit analysis or ion substitution detected no differences in Rs between CF and normal cells. 7. We conclude that abnormalities in both cellular Cl‐ permeability (reduced) and Na+ permeability (increased) are characteristic of the cultured CF respiratory epithelial cell. These data suggest that a defect in the regulation of apical membrane permeabilities is a central feature of this disease.
Comparison of potassium currents in rabbit atrial and ventricular cells.
Authors: Giles W R , Imaizumi Y
Published: December 2014

1. In rabbit and human hearts there are significant differences in the action potential configuration in atrium and ventricle, and the action potential waveform exhibits marked frequency dependence in both tissues. To study the ionic mechanism(s) of these phenomena, the size and time course of the potassium (K+) currents responsible for repolarization have been recorded from single cells using a whole‐cell microelectrode voltage clamp method. 2. At physiological heart rates, the action potential in atrial cells has a short plateau phase; however, the rapid early repolarization is strongly frequency dependent. Ventricular myocytes have a long plateau (400‐700 ms at 23 degrees C), and the late repolarizing phase of the action potential is much faster in ventricle than in atrium. 3. In both cell types, four different outward currents can be recorded: (i) a large transient outward current, It; (ii) IK(Ca), a smaller Ca2+‐dependent K+ current; (iii) IK, a small, maintained time‐ and voltage‐dependent delayed rectifier K+ current; (iv) IK1, an inwardly rectifying K+ current. 4. It, which is responsible for early repolarization, is much larger in atrium than in ventricle. It has very rapid activation and inactivation kinetics but a very slow time course of recovery from inactivation (tau = 5.4 s at 23 degrees C). Our results show that the reactivation kinetics of It are responsible for the pronounced dependence of the shape of the atrial action potential on stimulus frequency. 5. IK(Ca) is variable from cell to cell and is larger in atrium than in ventricle. In both cell types, IK(Ca) is much smaller than It. 6. The delayed rectifier current, IK, is very small and turns on relatively slowly in both cell types. It is therefore not activated strongly during the relatively short plateau of the atrial action potential. Even in ventricle, it contributes only a small repolarizing current. 7. IK1, the inward rectifier K+ current, is much larger in ventricle than in atrium. The current‐voltage relationship for IK1 in ventricle exhibits a negative slope conductance between ‐50 and 0 mV. IK1 is the outward current which generates the resting membrane potential and it modulates the final repolarization phase of the action potential in both cell types. 8. These data strongly suggest that the action potential configuration and its frequency dependence in rabbit atrial and ventricular cells are mainly due to the differences in sizes and kinetics of It and IK1.