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O Rougier

Publications and source records attributed to O Rougier.

At least 19 recordsLinked to original sources
PubMed2004

Volume-sensitive Cl- current in bovine adrenocortical cells: comparison with the ACTH-induced Cl- current.

In a previous study performed on zona fasciculata (ZF) cells isolated from calf adrenal glands, we identified an ACTH-induced Cl- current involved in cell membrane depolarization. In the present work, we describe a volume-sensitive Cl- current and compare it with the ACTH-activated Cl- current. Experiments were performed using the whole-cell patch-clamp recording method, video microscopy and cortisol-secretion measurements. In current-clamp experiments, hypotonic solutions induced a membrane depolarization to -22 mV. This depolarization, correlated with an increase in the membrane conductance, was sensitive to different Cl- channel inhibitors. In voltage-clamp experiments, hypotonic solution induced a membrane current that slowly decayed and reversed at -21 mV. This ionic current displayed no time dependence and showed a slight outward rectification. It was blocked to variable extent by different conventional Cl- channel inhibitors. Under hypotonic conditions, membrane depolarizations were preceded by an increase in cell volume that was not detected under ACTH stimulation. It was concluded that hypotonic solution induced cell swelling, which activated a Cl- current involved in membrane depolarization. Although cell volume change was not observed in the presence of ACTH, biophysical properties and pharmacological profile of the volume-sensitive Cl- current present obvious similarities with the ACTH-activated Cl- current. As compared to ACTH, hypotonic solutions failed to trigger cortisol production that was weakly stimulated in the presence of high-K+ solution. This shows that in ZF cells, membrane depolarization is not a sufficient condition to fully activate secretory activities.

Adrenocorticotropic Hormone↗
PubMed2000

Characterization of Na/Ca exchange in plasmalemmal vesicles from zona fasciculata cells of the bovine adrenal gland.

The presence of an Na/Ca exchange system in fasciculata cells of the bovine adrenal gland was tested using isolated plasmalemmal vesicles. In the presence of an outwardly Na(+) gradient, Ca(2+) uptake was about 2-fold higher than in K(+) condition. Li(+) did not substitute for Na(+) and 5 mM Ni(2+) inhibited Ca(2+) uptake. Ca(2+) efflux from Ca(2+)-loaded vesicles was Na(+)-stimulated and Ni(2+)-inhibited. The saturable part of Na(+)-dependent Ca(2+) uptake displayed Michaelis-Menten kinetics. The relationship of Na(+)-dependent Ca(2+) uptake versus intravesicular Na(+) concentration was sigmoid (apparent K(0.5) approximately 24 mM; Hill number approximately 3) and Na(+) acted on V(max) without significant effect on K(m). Na(+)-stimulated Ca(2+) uptake was temperature-dependent (apparent Q(10) approximately 2.2). The inhibition properties of several divalent cations (Cd(2+), Sr(2+), Ni(2+), Ba(2+), Mn(2+), Mg(2+)) were tested and were similar to those observed in kidney basolateral membrane. The above results indicate the presence of an Na/Ca exchanger located on plasma membrane of zona fasciculata cells of bovine adrenal gland. This exchanger displays similarities with that of renal basolateral cell membrane.

Adrenal Glands↗
PubMed2000

Opposite effects of halothane on guinea-pig ventricular action potential duration.

Halothane protects the heart against the reperfusion injury observed after an ischemia. In ischemic or anoxic conditions, a large ATP-sensitive K(+) (K(ATP)) conductance is supposed to provide an endogenous protection to the myocardium. In this study, we tested the possibility that halothane acted by modulating this conductance. Isolated guinea-pig cardiomyocytes were successively studied in current clamp and in voltage-clamp conditions. Action potentials regulation by halothane was tested in control conditions and in situations where the K(ATP) channels were activated. In control conditions, halothane decreased action potential duration of myocytes but did not significantly alter the inward rectifying K(+) current. Conversely, halothane lengthened action potential of cells in which the K(ATP) conductance was activated, by inhibiting the K(ATP) current. In ischemic conditions, simultaneous shortening of long action potentials and lengthening of shortened ones would be expected to homogenize the absolute refractory period at the border between normoxic and anoxic zones. This effect, together with a decrease in calcium load, could protect the myocardium against re-entrant arrhythmias.

Action Potentials↗
PubMed2000

Two types of pharmacologically distinct Ca(2+) currents with voltage-dependent similarities in zona fasciculata cells isolated from bovine adrenal gland.

Voltage-activated Ca(2+) currents, in zona fasciculata cells isolated from calf adrenal gland, were characterized using perforated patch-clamp recording. In control solution (Ca(2+): 2.5 mm) a transient inward current was followed, in 40% of the cells, by a sustained one. In 20 mm Ba(2+), 61% of the cells displayed an inward current, which consisted of transient and sustained components. The other cells produced either a sustained or a transient inward current. These different patterns were dependent upon time in culture. Current-voltage relationships show that both the transient and sustained components activated, peaked and reversed at similar potentials: -40, 0 and +60 mV, respectively. The two components, fully inactivated at -10 mV, were separated by double-pulse protocols from different holding potentials where the transient component could be inactivated or reactivated. The decaying phase of the sustained component was fitted by a double exponential (time constants: 1.9 and 20 sec at +10 mV); that of the transient component was fitted by a single exponential (time constant: 19 msec at +10 mV). Steady-state activation and inactivation curves of the two components were superimposed. Their half activation and inactivation potentials were similar, about -15 and -34 mV, respectively. The sustained component was larger in Ba(2+) than in Sr(2+) and Ca(2+). Ni(2+) (20 microm) selectively blocked the transient component while Cd(2+) (10 microm) selectively blocked the sustained one. (+/-)Bay K 8644 (0.5 microm) increased the sustained component and nitrendipine (0.5-1 microm) blocked it selectively. The sustained component was inhibited by calciseptine (1 microm). Both components were unaffected by omega-conotoxin GVIA and MVIIC (0.5 microm). These results show that two distinct populations of Ca(2+) channels coexist in this cell type. Although the voltage dependence of their activation and inactivation are comparable, these two components of the inward current are similar to T- and L-type currents described in other cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1998

Activation by angiotensin II of Ca(2+)-dependent K+ and Cl- currents in zona fasciculata cells of bovine adrenal gland.

The effects of angiotensin II (100 nM) on the electrical membrane properties of zona fasciculata cells isolated from calf adrenal gland were studied using the whole cell patch recording method. In current-clamp condition, angiotension II induced a biphasic membrane response which began by a transient hyperpolarization followed by a depolarization more positive than the control resting potential. These effects were abolished by Losartan (10(-5) M), an antagonist of angiotensin receptors of type 1. The angiotensin II-induced transient hyperpolarization was characterized in voltage-clamp condition from a holding potential of -10 mV. Using either the perforated or the standard recording method, a transient outward current accompanied by an increase of the membrane conductance was observed in response to the hormonal stimulation. This outward current consisted of an initial fast peak followed by an oscillating or a slowly decaying plateau current. In Cl(-)-free solution, the outward current reversed at -78.5 mV, a value close to EK. It was blocked by external TEA (20 mM) and by apamin (50 nM). In K(+)-free solution, the transient outward current, sensitive to Cl- channel blocker DPC (400 microM), reversed at -52 mV, a more positive potential than ECl. Its magnitude changed in the same direction as the driving force for Cl-. The hormone-induced transient outward current was never observed when EGTA (5 mM) was added to the pipette solution. The plateau current was suppressed in nominally CA(2+)-free solution (47% of cells) and was reversibly blocked by Cd2+ (300 microM) but not by nisoldipine (0.5-1 microM) which inhibited voltage-gated Ca2+ currents identified in this cell type. The present experiments show that the transient hyperpolarization induced by angiotensin II is due to Ca(2+)-dependent K+ and Cl- currents. These two membrane currents are co-activated in response to an internal increase of [Ca2+]i originating from intra- and extracellular stores.

Angiotensin II↗
PubMed1997

Similarity of ATP-dependent K+ channels in skeletal muscle fibres from normal and mutant mdx mice.

1. ATP-dependent K+ (KATP) channels were studied in fibres isolated from flexor digitorum brevis and interosseal skeletal muscles of normal and mutant mdx mice using the patch clamp technique in the presence of asymmetrical K+ concentrations (5 mM K+ in the pipette and in vivo intracellular [K+] or 145 mM K+ at the cytoplasmic face). 2. In cell-attached patches from mdx muscle fibres bathed in K(+)-rich solution, cell poisoning with fluorodinitrobenzene induced partially reversible opening of channels carrying an outward current of an amplitude of 1.2 pA at 0 mV. Exposure of fibres to the K+ channel opener cromakalim led to opening of the same type of channel. These channels were assumed to be KATP channels. 3. On excision of inside-out patches from mdx muscle fibres, in the absence of intracellular ATP, KATP channels were active: they carried a unitary outward current of 1.6 pA at 0 mV and were inhibited by intracellular ATP and glibenclamide. The number of KATP channels per patch was not significantly different in muscles from normal and mdx mice. 4. In inside-out patches, in the presence of 1 mM intracellular Mg2+, slope conductances of 21 and 20.3 pS were found for KATP channels in normal and mdx muscle, respectively. In the absence of Mg2+, slope conductances of KATP channels were 31.3 and 32 pS in normal and mdx muscle, respectively and KATP channel activity was augmented in mdx muscle in the same way as in normal muscle. Activity of the same KATP channel was observed in extensor digitorum longus muscle from normal and mdx mice. 5. In inside-out patches held at 0 mV, the relationship between KATP channel activity and intracellular ATP was described by a Hill equation: Ki values were 23 and 21 microM and Hill coefficients were 1.8 and 1.9 in normal and mdx muscle, respectively. 6. These results indicate that the distribution, the conductance properties and ATP sensitivity of KATP channels do not differ in normal and in mdx mouse skeletal muscle.

Adenosine Triphosphate↗
PubMed1997

Reduction of I(Ca,L) and I(to1) density in hypertrophied right ventricular cells by simulated high altitude in adult rats.

The present paper describes the effect of a simulated hypobaric condition (at the altitude of 4500 m) on morphological characteristics and on some ionic currents in ventricular cells of adult rats. According to current data, chronic high-altitude exposure led to mild right ventricular hypertrophy. Increase in right ventricular weight appeared to be due wholly or partly to an enlargement of myocytes. The whole-cell patch-clamp technique was used and this confirmed, by cell capacitance measurement, that chronic high-altitude exposure induced an increase in the size of the right ventricular cells. Hypertrophied cells showed prolongation of action potential (AP). Four ionic currents, playing a role along with many others in the precise balance of inward and outward currents that control the duration of cardiac AP, were investigated. We report a significant decrease in the transient outward (I(to1)) and in the L-type calcium current (I(Ca,L)) densities while there was no significant difference in the delayed rectifier current (I(K)) or in the inward rectifier current (I(K1)) densities in hypertrophied right ventricular cells compared to control cells. At a given potential the decrease in I(to 1) density was relatively more important than the decrease in I(Ca,L) density. In both cell types, all the currents displayed the same voltage dependence. The inactivation kinetics of I(to 1) and I(Ca,L) or the steady-state activation and inactivation relationships were not significantly modified by chronic high-altitude exposure. We conclude that chronic high-altitude exposure induced true right ventricular myocyte hypertrophy and that the decrease in I(to 1) density might account for the lengthened action potential, or have a partial effect.

Action Potentials↗
PubMed1996

Intracellular Ca2+ changes and Ca2+-activated K+ channel activation induced by acetylcholine at the endplate of mouse skeletal muscle fibres.

1. Enzymatically isolated skeletal muscle fibres were used to investigate the effects of applying acetylcholine (ACh) onto the endplate area on intracellular free calcium concentration ([Ca2+]i) measured using the indicator indo-1 and single channel activity using the patch clamp technique. 2. Using a Tyrode solution containing 5 microM tetrodotoxin (TTX) as extracellular solution, ACh applications (at 0.1 or 1 mM) onto the endplate induced intracellular free calcium transients the mean maximal amplitude of which was 360 +/- 30 nM from a mean resting value of 72 +/- 7 nM (n = 13). In cells bathed with a K(+)-rich solution (145 mM K+), applications of ACh (0.1 mM) induced transient rises in [Ca2+]i from a mean resting value of 53 +/- 7 nM to a maximum of 222 +/- 24 nM (n = 33). 3. In cell-attached membrane patches at the endplate membrane of muscle fibres bathed in a K(+)-rich external solution, using a pipette filled with Tyrode solution, external application of 0.1 mM ACh could induce a transient burst opening of channels carrying an outward current of an average amplitude of 4.6 +/- 0.2 pA at 0 mV (n = 8). 4. These channels were characterized as Ca2(+)-activated K+ channels. At 0 mV, in inside-out patches excised from the endplate membrane area, they displayed a conductance of 60 and 224 pS in the presence of Tyrode and K(+)-rich solution in the pipette, respectively. Half-maximum activation was found for a [Ca2+]i close to 4 microM. The channels showed a typical voltage dependence. In outside-out patches these channels were shown to be blocked by 100 nM charybdotoxin (CTX). 5. In fibres bathed in a Tyrode solution containing TTX (5 microM), CTX had no clear effect on the change in membrane voltage, recorded near the endplate with a single intracellular microelectrode, in response to the application of ACh. 6. Although the physiological relevance of this ACh-induced K+ channel activation remains unclear, results suggest that, in the presence of a physiological extracellular [Ca2+], Ca2+ entry through the endplate nicotinic receptors can produce a local increase in [Ca2+]i, sufficient to trigger the opening of Ca2+-activated K+ channels in the adjacent surface membrane.

Acetylcholine↗
PubMed1996

The transient outward current of isolated bovine adrenal zona fasciculata cells: comparison between standard and perforated patch recording methods.

Voltage-clamp experiments were performed on single bovine adrenal fasciculata cells in short-term primary culture using either standard (broken membrane) or perforated whole-cell patch clamp recording. The membrane current measured with the perforated method was dominated by a very stable transient outward current. By contrast, the transient outward current recorded using the standard method was unstable. The reversal potential of the transient outward current varied linearly with the logarithm of [K+]e with a slope of 47 mV per decade. The onset of activation was sigmoidal and was fitted with a power function where n = 4. Time constants ranged from 1 to 4 msec with a maximum at -25 mV. The steady-state activation curve spanned the voltage range -50 +80 mV without reaching a clear maximum. During a pulse, the current decayed in a biexponential manner. Time constants tau 1 and tau 2 were voltage-dependent and ranged from 50 to 200 msec respectively for a voltage step at +50 mV. The steady-state inactivation was dependent on the conditioning pulse duration. Using short conditioning pulses (1.2 sec), the curve which spanned the voltage range -40 to -20 mV, was 15 mV more positive than that obtained with longer conditioning pulses (60 sec). Time constants of this "very slow inactivation" process (tau vs) determined for voltage steps at -60 and -50 mV were 15 and 10 sec respectively. A "facilitation process" of the peak current was observed when the duration or the amplitude of conditioning pulses were increased in the voltage range -100 to -50 mV. Recovery from inactivation followed a biexponential time course which seemed a mixture of both inactivation processes. In some experimental conditions, isolated cells were able to produce overshooting action potentials. These results are discussed in relation with the membrane electrogenesis of this cell type.

Adrenal Cortex↗
PubMed1996

Picrotoxin potentiates contraction while inhibiting Ca current but increasing birefringence signal in frog skeletal muscle fibers.

In single frog skeletal muscle fibers, picrotoxin (5 mM) potentiated the voltage-dependent component of contractions in response to 2-s depolarizing pulses while greatly inhibiting the simultaneously recorded tubular Ca current in a normal-Ca, Na- and CI-deficient solution, provided the contractions were generated at long time intervals (2 min). In normal Ringer's solution, picrotoxin reversibly increased the amplitude of the early large birefringence signal and the amplitude and duration of the simultaneously recorded twitch tension, suggesting that the drug may increase, directly or indirectly, the release of Ca from the SR.

Animals↗
PubMed1995

Dose-dependent activation and block by bisG10, a K+ channel blocker, of mouse and frog skeletal muscle KATP channels.

The effects of a K+ channel blocker, bisG10, were examined on ATP-sensitive K+ (KATP) channels in membrane patches excised from mammalian and amphibian skeletal muscle fibres using the patch-clamp technique. At micromolar concentrations, bisG10, added on the intracellular side, induced a strong, reversible, flickery block of KATP channels. BisG10, added on the extracellular side, was about 100-fold less potent at inhibiting channel activity. At 10 nM, intracellular bisG10 increased KATP channel activity. This activation was independent of the presence of internal ATP or Mg2+. The inhibitory effect of bisG10 most likely arose from open-channel block whereas activation could result from more complex, indirect interactions.

Adenosine Triphosphate↗
PubMed1995

Activation of ATP-dependent K+ channels by metabolic poisoning in adult mouse skeletal muscle: role of intracellular Mg(2+) and pH.

1. The effects of metabolic poisoning, intracellular Mg(2+) and pH on ATP-dependent K+ (K+ATP) channels were examined in adult mouse isolated skeletal muscle fibres using the patch clamp technique. 2. In cell-attached membrane patches, while openings of one kind of channel could only rarely be detected under control conditions, cell poisoning with fluorodinitrobenzene (FDNB), dinitrophenol (DNP) and cyanide (CN) induced a strong and partially reversible increase in channel activity. 3. Slope conductance and glibenclamide sensitivity of this outward current indicated that the channel activated during poisoning was the K+ATP channel. 4. Single channel current amplitude was reduced during poisoning, but remained unchanged when activation of the K+ATP channel was induced by cromakalim. 5. In inside-out membrane patches, in the absence of intracellular ATP, intracellular application of Mg2+ decreased channel activity and single channel current amplitude. Inhibition of K+ATP channels by ATP was also reduced. 6. In the absence of intracellular ATP, a decrease in intracellular pH induced a reduction in channel activity and single channel current amplitude. Inhibition of K+ATP channels by ATP was also reduced. 7. The reduction of single channel current amplitude during poisoning was attributed to an increase in intracellular Mg2+ concentration caused by a fall in intracellular ATP concentration. These results also show that metabolic poisoning causes direct activation of K+ATP channels in skeletal muscle, and that is activation is at least partially mediated through an increase in intracellular Mg(2+) concentration and a decrease in intracellular pH.

2,4-Dinitrophenol↗
PubMed1994

The effects of chloride ions in excitation-contraction coupling and sarcoplasmic reticulum calcium release in twitch muscle fibre.

Using the sucrose vaseline gap technique, experiments were carried out on isolated frog twitch muscle fibre to investigate the role of chloride ions in excitation-contraction coupling. In current clamp conditions, replacement of chloride ions by impermeant anions led to an increase of the amplitude of the early after potential and of the amplitude of the twitch. Addition of a chloride channel blocker, anthracene-9-carboxylic acid gave similar results. In voltage clamp conditions, replacement of chloride ions by impermeant anions induced a decrease of the outward current and an increase of both the amplitude of the contraction and of the resting tension. Addition of anthracene-9-carboxylic acid gave similar results except that resting tension was not modified. Replacement of chloride ions by impermeant anions resulted in a shift of the tension-voltage relationship toward negative potentials and in an increase of the amplitude of the contraction at all potentials. Outward currents were also reduced at all potentials but no shift of the current-voltage relationship was observed. Similar results were obtained upon addition of anthracene-9-carboxylic acid. Rapid filtration experiments were performed on isolated sarcoplasmic reticulum vesicles to study the role of chloride ions in Ca2+ release. Under conditions where KCl was present in the intra- and extravesicular media, removal of chloride ions from the release solution produced a 2-fold increase in the rate of Ca(2+)-induced Ca2+ release. Together, these results suggest that, besides their involvement in the action potential time course, chloride ions could exert a negative control on the sarcoplasmic reticulum Ca2+ release.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

Inward barium current and excitation-contraction coupling in frog twitch muscle fibres.

The role of barium ions in excitation-contraction coupling was studied in single isolated frog semitendinosus fibres. Simultaneous recordings of membrane currents and contraction under voltage-clamp conditions in a sucrose-vaseline gap device show that barium ions have a reversible inhibiting effect on contraction. This inhibiting action was correlated to the entry of barium ions via the DHP-sensitive tubular calcium channel. Cytological observations and X-ray microanalysis performed on the fibres used in the electrophysiological experiments indicate that barium ions do not accumulate in the junctional sarcoplasmic reticulum; they can freely diffuse in the intermyofibrillar space and they accumulate in mitochondria. Calcium release experiments performed on isolated sarcoplasmic reticulum vesicles show that barium ions are not able to induce calcium release from calcium-loaded vesicles, they behave as calcium release inhibitors. These results are discussed in relation with the possible role of the slow Ca current in excitation-contraction coupling.

Animals↗
PubMed1992

Reappraisal of the role of sodium ions in excitation-contraction coupling in frog twitch muscle.

Tetanic and twitch tension were recorded on isolated frog twitch fibres under experimental conditions modifying the influx of sodium ions. In current clamp conditions replacing Li+ for Na+ did not modify the electrical activity but drastically decreased the plateau of tetanic tension. In voltage clamp conditions replacing Li+ for Na+ did not modify the inward currents but induced a marked decrease of the plateau of the tetanic tension for depolarizations between the activation threshold and the reversal potential of sodium current. Under veratridine treatment, during tetanic depolarization, a slow inward sodium (or lithium) current developed. This induced a parallel increase of the tetanic tension which was much more pronounced in sodium than in lithium containing solution. The twitch tension obtained during short depolarization was increased by greater than 100% during veratridine treatment with a sizeable decrease (40%) of the delay between the end of depolarization and the beginning of tension. All these results could be reproduced in calcium-free solution. Our data confirm that the entry of sodium ions (and to a lesser extent of lithium ions) is able to modulate the release of calcium from the sarcoplasmic reticulum (SR). We discuss these results in terms of a model where sodium ions entering the compartment between the tubular membrane and the SR junctional membrane carry counter charges through the SR K+ channels and help to maintain the SR Ca2+ release. This could occur in particular during a physiological tetanic contraction where the junctional compartment is probably filled with Na+ ions and depleted of K+ ions.

Action Potentials↗
PubMed1991

Action of heptaminol hydrochloride on contractile properties in frog isolated twitch muscle fibre.

1. Heptaminol stopped or delayed the progressive decline in tension which characterizes the phenomenon of fatigue in frog isolated twitch muscle fibre. 2. Heptaminol had no action on the sodium, potassium and calcium voltage-dependent ionic conductances. 3. The hypothesis of an action via an internal alkalinization was tested by comparison with the action of NH4Cl. Both substances increased the tension. 4. The action of heptaminol was suppressed in sodium-free (TRIS) solution or in the presence of amiloride while the action of NH4Cl was always observed. 5. These results could be explained by a stimulation of the Na/H antiport by heptaminol.

Action Potentials↗
PubMed1991

The effects of sodium removal on the two types of calcium currents in single frog atrial cells.

The effects of sodium removal on the two types of calcium currents were studied in enzymatically dispersed frog (Rana esculenta) atrial myocytes with the single pipette patch-clamp technique. Reduction of calcium currents was recorded when NaCl was replaced either by TEACl, LiCl, TrisCl, cholineCl or by mannitol. An involvement of the Na-Ca exchange mechanism could be ruled out since the decrease was also observed after replacing external Ca with Ba. The slight shift of the apparent reversal potential recorded in our study suggests that the inward flow of Na ions through calcium channels does not contribute significantly to the L-type calcium current. Once again, the slight negative shift of the steady-state inactivation curve of the L-type calcium current cannot explain this decrease while no shift was recorded for the T-type calcium current. Even if a TTX-resistant Na current was recorded from a few cells this current cannot explain the decrease of calcium currents which was always observed upon sodium removal. To date we have no explanation for this effect.

Animals↗