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J W Fiolet

Publications and source records attributed to J W Fiolet.

At least 19 recordsLinked to original sources
PubMed2000

Presence of functional sarcoplasmic reticulum in the developing heart and its confinement to chamber myocardium.

During development fast-contracting atrial and ventricular chambers develop from a peristaltic-contracting heart tube. This study addresses the question of whether chamber formation is paralleled by a matching expression of the sarcoplasmic reticulum (SR) Ca(2+) pump. We studied indo-1 Ca(2+) transients elicited by field stimulation of linear heart tube stages and of explants from atria and outflow tracts of the prototypical preseptational E13 rat heart. Ca(2+) transients of H/H 11+ chicken hearts, which constitute the prototypic linear heart tube stage, were sensitive to verapamil only, indicating a minor contribution of Ca(2+)-triggered SR Ca(2+) release. Outflow tract transients displayed sensitivity to the inhibitors similar to that of the linear heart tube stages. Atrial Ca(2+) transients disappeared upon addition of ryanodine, tetracaine, or verapamil, indicating the presence of Ca(2+)-triggered SR Ca(2+) release. Quantitative radioactive in situ hybridization on sections of E13 rat hearts showed approximately 10-fold higher SERCA2a mRNA levels in the atria compared to nonmyocardial tissue and approximately 5-fold higher expression in compact ventricular myocardium. The myocardium of atrioventricular canal, outflow tract, inner curvature, and ventricular trabecules displayed weak expression. Immunohistochemistry on sections of rat and human embryos showed a similar pattern. The significance of these findings is threefold. (i) A functional SR is present long before birth. (ii) SR development is concomitant with cardiac chamber development, explaining regional differences in cardiac function. (iii) The pattern of SERCA2a expression underscores a manner of chamber development by differentiation at the outer curvature, rather than by segmentation of the linear heart tube.

Animals↗
PubMed2000

SR calcium depletion following reversal of the Na+/Ca2+-exchanger in rat ventricular myocytes.

We previously reported that cytosolic calcium transiently increases after reversal of the sarcolemmal Na+/Ca2+-exchanger. Calcium released from sarcoplasmic reticulum (SR) constituted the major part of this cytosolic transient. The aim of this study was to test whether reversal of the Na+/Ca2+-exchanger affects SR calcium content, and whether altered SR calcium content is associated with direct triggering of SR calcium release or calcium release secondary to SR calcium overload. To this purpose we studied the change of SR calcium content after reversal of the Na+/Ca2+-exchanger and the dependence on the magnitude of change of its free energy (delta Gexch) in isolated rat ventricular myocytes. The Na+/Ca2+-exchanger was reversed by abrupt reduction of extracellular sodium ([Na+]o). The magnitude of change of deltaGexch was varied with [Na+]o. Cytosolic free calcium ([Ca2+]i) was measured with indo-1 and SR calcium content was estimated from the increase of [Ca2+]i after rapid cooling (RC). SR function was manipulated either by blockade of the SR Ca2+-ATPase with thapsigargin or by blockade of SR calcium release channels with tetracaine. Reversal of the Na+/Ca2+-exchanger caused a transient increase of [Ca2+]i of about 180 s duration with a time to peak of about 30 s. During the first 30 s rapid small amplitude cytosolic calcium fluctuations were superimposed on this transient. The magnitude of the response of [Ca2+]i to RC, during the course of the cytosolic [Ca2+]i transient, also transiently increased from 174 in control myocytes to 480 nmol/l at the time of the peak value. After correction of [Ca2+]i data for the fraction of mitochondrially compartmentalized indo-1 and mitochondrial calcium, total calcium released from SR after RC was calculated with the use of literature data on cytosolic calcium buffer capacity. Contrary to the measured RC-dependent increase of measured [Ca2+]i, after reversal of the Na+/Ca2+-exchanger, calculated total calcium released from SR transiently decreased. The extent of SR calcium depletion after reversal of the Na+/Ca2+-exchanger increased with the magnitude of change of deltaGexch. Restitution of [Na+]o 30 s after reversal of the Na+/Ca2+-exchanger, greatly accelerated both recovery of [Ca2+]i and SR calcium content. Pretreatment of myocytes with thapsigargin caused almost entire depletion of SR and substantial reduction of the cytosolic transient of [Ca2+]i following reversal of the Na+/Ca2+-exchanger. Application of tetracaine hardly affected SR calcium content, but caused an increase of the SR calcium content following reversal of the Na+/Ca2+-exchanger, while the cytosolic transient increase of [Ca2+]i was substantially reduced. We conclude that reversal of the Na+/Ca2+-exchanger directly triggers SR calcium release and decreases SR calcium content in a deltaGexch dependent manner.

Animals↗
PubMed1998

Energy-dependent transport of calcium to the extracellular space during acute ischemia of the rat heart.

OBJECTIVE: Acute ischemia is associated with rapidly decreasing contractility and Ca2+-transients. Diastolic intracellular Ca2+, however, only mildly increases until development of contracture. The purpose of this study was to investigate whether changes of cellular calcium handling during the early phase of ischemia are associated with active sarcolemmal calcium transport. METHODS: Changes of extracellular concentration of calcium ([Ca2+]o) and tetramethylammonium ([TMA+]o), to estimate extracellular space, were simultaneously measured with ion-specific electrodes in the globally ischemic rat heart. The magnitude and direction of sarcolemmal calcium transport were calculated from [Ca2]o corrected for changed extracellular water content. Energy dependence of sarcolemmal calcium transport was investigated by application of iodoaceticacid (IAA) to inhibit anaerobic glycolysis, and the involvement of the sarcoplasmic reticulum (SR) was studied by application of thapsigargin. The effect of anoxia and thapsigargin on cytosolic and SR calcium was studied in isolated myocytes with the fluorescent indicator indo-1. RESULTS: [Ca2+]o increased and extracellular space gradually decreased in the ischemic intact heart. During the first 7 min, the increase of [Ca2+]o was associated with net outward transport of calcium. Subsequently, net re-uptake occurred. IAA completely abolished outward transport and influx was accelerated and enhanced. Application of thapsigargin attenuated outward transport. In electrically-stimulated myocytes, anoxia caused little change of diastolic calcium and depletion of SR. Thapsigargin reduced both calcium transient amplitude and SR calcium without affecting diastolic calcium. During three successive short episodes of ischemia/reperfusion (preconditioning), outward transport of calcium progressively decreased. CONCLUSION: During the early phase of global ischemia, energy dependent transport of calcium to the extracellular space occurs. At least part of this calcium originates from SR. During the later stage of ischemia, re-uptake of calcium occurs, which is associated with development of contracture.

Animals↗
PubMed1998

Cytoplasmic sodium, calcium and free energy change of the Na+/Ca2+-exchanger in rat ventricular myocytes.

The relationship between changing driving force of the Na+/Ca2+-exchanger (deltaG(exch)) and associated cytosolic calcium fluxes was studied in rat ventricular myocytes. DeltaG(exch) was abruptly reversed by the reduction of extracellular sodium ([Na+]o) with or without sustained depolarization by the elevation of potassium ([K+]o). Cytosolic sodium ([Na+]i) and calcium ([Ca2+]i) were measured with SBFI and indo-1 respectively and the time course of recovery of deltaG(exch) was calculated. Following abrupt reversal of deltaG(exch) from +4.1 to -9.2 kJ/mol [Na+]i exponentially decreased from 9.6-2.5 mmol/l (t(1/2) about 30 s) and [Ca2+]i transiently increased to a peak value after about 30 s. Negative values of deltaG(exch) were associated with an increase and positive values with a decrease of [Ca2+]i. Equilibrium (deltaG(exch) = 0) was reached after about 30 s coinciding with the time to peak [Ca2+]i. After 180 s deltaG(exch) reached a new steady state at +3.5 kJ/mol. Inhibition of SR with ryanodine or thapsigargin reduced the amplitude of the [Ca2+]i transient and shifted its peak to 80 s, but did not affect the time course of [Na+]i changes. In the presence of ryanodine or thapsigargin the time required for deltaG(exch) to recover to equilibrium was also shifted to 80 s. When we changed the deltaG(exch) to the same extent by the reduction of [Na+]o in combination with a sustained depolarization, [Na+]i decreased less and the amplitude of [Ca2+]i transient was much enhanced. This increase of [Ca2+]i was completely abolished by verapamil. DeltaG(exch) only recovered to a little above equilibrium (+1 kJ/mol). Inhibition of the Na+/K+-ATPase with ouabain entirely prevented the decrease of [Na+]i and caused a much larger increase of [Ca2+]i, which remained elevated; deltaG(exch) recovered to equilibrium and never returned to positive values. The rate of change of total cytosolic calcium was related to deltaG(exch), despite the fact that the calcium flux associated with the exchanger itself contributed only about 10%; SR related flux contributed by about 90% to the rate of change of total cytosolic calcium. In summary, reduction of [Na+]o causes reversal of the Na+/Ca2+-exchanger and its driving force deltaG(exch), a transient increase of [Ca2+]i and a decrease of [Na+]i. The influx of calcium associated with reversed deltaG(exch) triggers the release of calcium from SR. Both the decrease of [Na+]i and the increase of [Ca2+]i contribute to the recovery of deltaG(exch) to equilibrium. The time at which deltaG(exch) reaches equilibrium always coincides with the time to peak of [Ca2+]i transient. Activation of the Na+/K+-ATPase is required to reduce [Na+]i and recover deltaG(exch) to positive values in order to reduce [Ca2+]i. We conclude that deltaG(exch) is a major regulator of cytosolic calcium by interaction with SR.

Animals↗
PubMed1997

Small changes of cytosolic sodium in rat ventricular myocytes measured with SBFI in emission ratio mode.

The spectral properties of SBFI (sodium-binding benzofurzan isophthalate) were re-examined to arrive at a more specific and sensitive method to measure small changes of intracellular sodium ([Na+]i) particularly at low concentration. Relative to spectra of SBFI in protein- and cell-free solution, binding of SBFI to intracellular proteins caused a shift of excitation and emission spectra, and increased quantum efficiency. Excitation of SBFI at 340 nm caused an exclusively sodium-dependent fluorescence from 400-420 nm, and hardly any change of fluorescence above 530 nm upon replacing sodium by potassium. Due to these spectral and quantum efficiency changes, SBFI excitated at 340 nm can be used in a dual emission ratio mode to measure [Na+]i. In dual emission ratio mode (410 and 590 nm, respectively), the fluorescence ratio increased by a factor of 13 upon replacing sodium for potassium. The apparent equilibrium constant measured in single isolated rat ventricular myocytes was 22.5+/-0.3 mmol/l. Control [Na+]i was 9.6+/-0.4 mmol/l. After abrupt reduction of extracellular sodium from 156 to 29 or 11 mmol/l, [Na+]i decreased mono-exponentially to 2.5+/-0.3 and 1.9+/-0. 3 mmol/l, respectively, with a rate constant of about 0.02/s. We conclude that SBFI used in dual emission mode provides a more sensitive and more specific method to measure small changes of [Na+]i in single myocytes down to cytosolic sodium concentration as low as about 1 mmol/l.

Animals↗
PubMed1996

The origin of increased cytoplasmic calcium upon reversal of the Na+/Ca(2+)-exchanger in isolated rat ventricular myocytes.

Reversal of the driving force of the Na+/Ca(2+)-exchanger (delta Gexch) by a sufficiently large change of the transsarcolemmal electrochemical potential of sodium and calcium causes a transient increase of cytoplasmic calcium ([Ca2+]i). The objective of this study was to investigate the origin of this transient increase of calcium. In isolated quiescent rat ventricular myocytes delta Gexch was abruptly changed by reduction of extracellular sodium ([Na+]o), with or without a simultaneous increase of potassium ([K+]o) or calcium ([Ca2+]i). [Ca2+]i was measured with indo-1. A particular change of delta Gexch induced either by reduction of [Na+]o alone or in combination with increase of [Ca2+]o, produced a transient increase of [Ca2+]i of the same magnitude with a maximum after around 30s. The response of [Ca2+]i was insensitive to verapamil, but was greatly reduced by ryanodine, thapsigargin and caffeine, indicating a large contribution originating from the sarcoplasmic reticulum (SR). The magnitude of the response of [Ca2+]i and also the contribution from SR increased with increasing change of delta Gexch. A particular change of delta Gexch. Induced by a reduction of [Na+]o in combination with membrane depolarization (increase of [K+]o) increased the response of [Ca2+]i, compared that induced by reduction of [Na+]o alone at the same change of delta Gexch. This effect increased with the degree of depolarization, and was completely abolished by verapamil. Also in depolarized cells the response of [Ca2+]i was reduced by ryanodine. However, the contribution from SR to the response did not depend on the degree of depolarization, but only on the magnitude of the change of delta Gexch. Inhibition of the Na+/Ca(2+)-exchanger by Ni2+ almost completely abolished the response of [Ca2+]i to reduction of [Na+]o. Restitution of [Na+]o during the course of the calcium response greatly accelerated the rate of decay of [Ca2+]i. It is concluded that in quiescent rat ventricular myocytes, a large part of the transient increase of cytoplasmic calcium associated with reversal of the driving force of the Na+/Ca(2+)-exchanger originates from SR. Reversal of the exchanger combined with sustained depolarization increased the transient of [Ca2+]i, but the extra influx of calcium associated with depolarization did not affect the contribution from SR.

Animals↗
PubMed1996

Intracellular Ca2+, intercellular electrical coupling, and mechanical activity in ischemic rabbit papillary muscle. Effects of preconditioning and metabolic blockade.

During myocardial ischemia, electrical uncoupling and contracture herald irreversible damage. In the present study, we tested the hypothesis that an increase of intracellular Ca2+ is an important factor initiating these events. Therefore, we simultaneously determined tissue resistance, mechanical activity, pH(0), and intracellular Ca2+ (with the fluorescent indicator indo 1, Molecular Probes, Inc) in arterially perfused rabbit papillary muscles. Sustained ischemia was induced in three experimental groups: (1) control, (2) preparations preconditioned with two 5-minute periods of ischemia followed by reperfusion, and (3) preparations pretreated with 1 mmol/L iodoacetate to block anaerobic metabolism and minimize acidification during ischemia. In a fourth experimental group, intracellular Ca2+ was increased under nonischemic conditions by perfusing with 0.1 mmol/L ionomycin and 0.1 mumol/L gramicidin. Ca2+ transients and contractions rapidly disappeared after the induction of ischemia. In the control group, diastolic Ca2+ began to rise after 12.6 +/- 1.3 minutes of ischemia; uncoupling, after 14.5 +/- 1.2 minutes of ischemia; and contracture, after 12.6 +/- 1.5 minutes of ischemia (mean +/- SEM). Preconditioning significantly postponed Ca2+ rise, uncoupling, and contracture (21.5 +/- 4.0, 24.0 +/- 4.1, and 23.0 +/- 5.3 minutes of ischemia, respectively). Pretreatment with iodoacetate significantly advanced these events (1.9 +/- 0.7, 3.6 +/- 0.9, and 1.9 +/- 0.2 minutes of ischemia, respectively). In all groups, the onset of uncoupling always followed the start of Ca2+ rise, whereas the start of contracture was not different from the rise in Ca2+. Perfusion with ionomycin and gramicidin permitted estimation of a threshold [Ca2+] for electrical uncoupling of 685 +/- 85 nmol/L. In conclusion, the rise in intracellular Ca2+ is the main trigger for cellular uncoupling during ischemia. Contracture is closely associated with the increase of intracellular Ca2+ during ischemia.

Animals↗
PubMed1995

The relation between extracellular potassium concentration and pH in the border zone during regional ischemia in isolated porcine hearts.

During regional ischemia gradients of extracellular potassium concentration ([K+]o) and extracellular pH (pHo) exist. In globally ischemic papillary muscles increased PCO2 causes a rise in [K+]o. We studied whether pHo and [K+]o are causally related during acute regional ischemia in the isolated blood-perfused pig heart. Multiple pH- or K(+)-sensitive electrodes were inserted in the left ventricular midmyocardium. Local electrograms and ionic data were simultaneously acquired. Regional ischemia was produced by interrupting left anterior descending (LAD) artery flow (10 min). Up to 5 mm from the electrophysiological border the pH-K relation deviated from that in the central ischemic zone. Respiratory acidosis (pH about 7.10) of the perfusate in the presence of LAD-ischemia caused acidification of the ischemic border zone without a local change in [K+]o. We conclude that pHo changes are not related to changes of intramural [K+]o in the lateral border zone during regional ischemia.

Animals↗
PubMed1995

Intracellular [Ca2+] and Vo2 after manipulation of the free-energy of the Na+/Ca(2+)-exchanger in isolated rat ventricular myocytes.

We have investigated whether the Na+/Ca(2+)-exchanger has a functional regulatory role in the control of oxidative metabolism in suspensions of isolated rat ventricular myocytes. Therefore we simultaneously measured intracellular [Ca2+] ([Ca2+]i) with Indo-1 and respiratory rate (Vo2) after abrupt manipulation of the free-energy of the Na+/Ca(2+)-exchanger (delta Gexch). The average fraction of viable myocytes was about 90% (82% rod-shaped plus 8% viable round cells). delta Gexch was manipulated either by an abrupt decrease of [Na+]o (in combination with an increase of [K+]o or [Ca2+]o) or by changing membrane potential and/or intracellular cation activities with the use of gramicidin or veratridine. A change of extracellular cation composition caused a transient increase of [Ca2+]i and Vo2, with peak values after 30 to 40 s and a new steady state near control values after 180 to 240 s. Peak values of the transients were associated with the magnitude of the thermodynamic disturbance. Inhibition of sodium-pump activity with ouabain greatly enhanced peak values and reduced the rate of return to a new steady state. Reversal of the initial disturbance of delta Gexch by restoring [Na+]o or reduction of [Ca2+]o during the time course of the transients greatly accelerated return to a new steady-state. An increase of sarcolemmal sodium permeability with the Na-channel ligand veratridine or manipulation of [Na+]i and [K+]i with the Na+/K(+)-exchanger gramicidin caused monophasic increase of both [Ca2+]i and Vo2. The relationship between VO2 and [Ca2+]i was the same, irrespective of the nature of the intervention (either extracellular or intracellular manipulation of delta Gexch). We conclude that cytoplasmic [Ca2+] (thermodynamically controlled by the Na+/Ca(2+)-exchanger) is a major regulator of the respiratory rate in (quiescent) myocytes.

Animals↗
PubMed1992

The premature beat.

Explore the source record for details and available documents.

Cardiac Complexes, Premature↗
PubMed1992

Reperfusion arrhythmias in isolated perfused pig hearts. Inhomogeneities in extracellular potassium, ST and TQ potentials, and transmembrane action potentials.

We recorded direct current electrograms and local [K+]o at multiple sites and transmembrane potentials at selected sites during reperfusion after 5 minutes and 10 minutes of regional ischemia in isolated perfused pig hearts. After 10 minutes of ischemia, the incidence of ventricular fibrillation (VF) was 38%. At 80-90 seconds after reperfusion, [K+]o was 0.8 mM less than in normal tissue in half of the reperfused tissue, especially in the border zone. This was associated with TQ elevation of +4.5 mV and large peaked T waves. The latter was caused by an abrupt decrease of action potential duration in reperfused tissue, leading to a difference of up to 165 msec with normal tissue. Reperfusion VF started with a closely coupled ventricular premature beat. Activation block between reperfused and normal tissue permitted reentrant activation, leading to VF. Pretreatment with ryanodine (10(-6) M) and reperfusion with elevated [K+] (both of which prevent delayed afterdepolarizations) did not prevent closely coupled ventricular premature beats or VF. Five minutes of ischemia never caused VF. K+ depletion and TQ elevation in the reperfused zone was less frequent and smaller (-0.4 mM and 1.8 mV, respectively). Peaked T waves did not occur, and shortening of the action potential duration was less. We conclude that extracellular K+ depletion and marked action potential duration shortening in the reperfused tissue play a role in the genesis of reperfusion VF, which is caused by reentry. The closely coupled ventricular premature beat that initiates reentry is not caused by delayed afterdepolarizations but most likely by intramural reentry.

Action Potentials↗
PubMed1991

Transsarcolemmal sodium-calcium exchange and myocardial oxygen consumption in isolated rat ventricular myocytes.

We studied oxygen consumption and energy metabolism in isolated rat ventricular myocytes which were subjected to an abrupt change in the cation composition of the extracellular medium ('transition'); extracellular [Na+] was decreased either alone or in combination with a change of [K+] or [Ca2+]. The magnitude of change of the cation concentration(s) was varied. The respiratory rate (vO2) of myocytes changed biphasically after such a transition. vO2 increases to a maximum after about 25 to 30 s and returns to almost control after 180 to 200 s. vO2-max depends on both the nature of the cation(s) of which the concentration(s) are varied and on the magnitude of these change(s); vO2-max can almost be as high as that induced by uncoupling of oxidative phosphorylation with DNP. The free energy of hydrolysis of cytoplasmic ATP hardly decreases after transition. Cell viability remains unaltered, although an increasingly larger fraction of rod-shaped cells transform to a hypercontracted state with increasing magnitude of the extracellular ion concentration change. Reversal of the ionic change or addition of EGTA at 30 s after transition accelerates the return of vO2 to the value prior to transition. In the presence of ouabain, vO2-max is higher and return to control is slower and incomplete. The total amount of oxygen consumption after transition, is linearly related to the initial change of the free energy of the Na+/Ca(2+)-exchanger caused by the cation concentration change(s); this relationship does not depend on the nature of the cation(s) changed. We conclude that the transient increase of vO2 after transition is regulated by intracellular free [Ca2+], which transiently increases. This transient increase is caused by change of the thermodynamic driving force on the Na+/Ca(2+)-exchanger after transition.

Adenosine Triphosphate↗
PubMed1990

Potassium accumulation in the globally ischemic mammalian heart. A role for the ATP-sensitive potassium channel.

We investigated the contribution of opening of the ATP-sensitive K+ channel to extracellular accumulation of K+ during ischemia with the use of glibenclamide, a specific blocker of this K+ channel. To characterize the electrophysiological effects of glibenclamide during metabolic inhibition (by either application of dinitrophenol or hypoxia) we performed patch-clamp studies in isolated membrane patches of guinea pig myocytes and in intact guinea pig myocytes and studied action potential parameters in isolated superfused guinea pig papillary muscle. We studied the effect of glibenclamide on extracellular accumulation of K+ and H+ in isolated retrogradely perfused globally ischemic hearts of rat, guinea pig, and rabbit. Experimental evidence is presented that supports the conclusions that glibenclamide 1) effectively blocks open K+ATP channels, 2) reverses the dinitrophenol-induced increase of the outward current and prevents the hypoxia-induced shortening of the action potential, 3) decreases the rate of K+ accumulation during the first minutes of ischemia in stimulated hearts, an effect which was entirely absent in quiescent hearts, and 4) does not influence the rate and extent of ischemia-induced extracellular acidification.

Action Potentials↗
PubMed1989

Distribution of extracellular potassium and electrophysiologic changes during two-stage coronary ligation in the isolated, perfused canine heart.

We studied the relation between [K+]o and the electrophysiologic changes during a "Harris two-stage ligation," which is an occlusion of a coronary artery, preceded by a 30-minute period of 50% reduction of flow through the artery. This two-stage ligation has been reported to be antiarrhythmic. Local direct current electrograms and [K+]o signals from up to 48 intramural sites were simultaneously recorded in isolated, perfused dog hearts. A second period of one-stage ligation was compared with a consecutive two-stage ligation because reproducibility in [K+]o and electrophysiologic changes are established only after the first period of ischemia. In control experiments, no difference was found between the second and third period of one-stage ligation in the electrophysiologic changes and in increases in [K+]o. After complete occlusion during two-stage ligation, activation block in the ischemic tissue occurred about 6 minutes earlier than during one-stage ligation, but the average potassium concentration at which block occurred was identical. This [K+]o during total ischemia was achieved earlier during two-stage ligation than during one-stage ligation. No indication was found for a large decrease of intracellular potassium content during the period of low flow perfusion. Early activation block may explain the previously reported reduced incidence of ventricular fibrillation during two-stage ligation.

Animals↗