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D Feuvray

Publications and source records attributed to D Feuvray.

At least 19 recordsLinked to original sources
PubMed2000

Slowly inactivating component of sodium current in ventricular myocytes is decreased by diabetes and partially inhibited by known Na(+)-H(+)Exchange blockers.

Recent evidence has suggested a major role for a slowly inactivating component of Na(+)current (I(NaL)) as a contributor to ischemic Na(+)loading. The purposes of this study were to investigate veratrine and lysophosphatidylcholine (LPC)-induced I(NaL)in single ventricular myocytes of normal and diabetic rats and to analyse the effects on this current of three pharmacological agents, known as Na(+)/H(+)exchange inhibitors, whose selectivity has been questioned in several studies. A decrease in Na(+)/H(+)exchange activity has been previously shown to be associated with diabetes, and this has been found to confer some protection to the diabetic heart after an episode of ischemia/reperfusion. Recordings were made using the whole-cell patch-clamp technique. I(NaL)was stimulated either by veratrine (100 mg/ml) or by LPC (10 micromol/l) applied extracellularly. Veratrine as well as LPC-induced I(NaL)was found to be significantly decreased in ventricular myocytes isolated from diabetic rat hearts. Veratrine- and LPC-induced I(NaL)in ventricular myocytes of normal rats was significantly (in the range 10(-7)to 10(-4)mol/l) inhibited by the Na(+)/H(+)exchange blockers HOE 694, EIPA and HOE 642. HOE 694 was the most potent inhibitor, followed by the amiloride derivative EIPA and HOE 642. The sensitivity of veratrine-induced I(NaL)to inhibition by HOE 694 and EIPA was markedly reduced in diabetic ventricular myocytes, with no observed inhibition by HOE 642. These data may have important implications as to the protection that may be afforded against ischemic and reperfusion injury, especially during ischemia and when ischemia occurs in a diabetic situation.

Amiloride↗
PubMed2000

Changes in intracellular sodium and pH during ischaemia-reperfusion are attenuated by trimetazidine. Comparison between low- and zero-flow ischaemia.

OBJECTIVE: The aim of this study was to investigate whether trimetazidine (TMZ; 10(-6)M), which has been shown to inhibit fatty acid oxidation, reduces the ionic imbalance induced by ischaemia and reperfusion, especially through an attenuation in intracellular changes in H(+) and Na(+). METHODS: Isovolumic rat hearts receiving 5.5 mM glucose and 1.2 mM palmitate as metabolic substrates were exposed to zero-flow ischaemia (TI) or low-flow ischaemia (LFI - coronary flow decreased by an average of 90%) (30 min at 37 degrees C) and then reperfused. 23Na nuclear magnetic resonance (NMR) spectroscopy was used to monitor intracellular Na(+) (Na(+)(i)) and 31P NMR spectroscopy was used to monitor intracellular pH (pH(i)). RESULTS: During LFI the major effect of TMZ was a significant reduction in intracellular acidosis, whereas during TI the main effect of TMZ was a significant reduction in Na(+)(i) gain. In addition, the further gain in Na(+)(i) that occurred during the first minutes of reperfusion following TI, and to a far lesser extent following LFI, was suppressed in TMZ-treated hearts and also suppressed when hearts were perfused without fatty acid. In both LFI and TI, TMZ-induced attenuation of ionic imbalance was associated with a significantly improved recovery of ventricular function on reperfusion, as assessed by a lower increase in diastolic pressure and an increased recovery of developed pressure. CONCLUSION: Our data provide evidence that specific myocardial metabolic modulation plays a significant role in reducing ionic imbalance during ischaemia and reperfusion.

Analysis of Variance↗
PubMed1999

Decrease in sodium-calcium exchange and calcium currents in diabetic rat ventricular myocytes.

This study was designed in order to gain insight into possible changes in the inward sodium-calcium exchange current (INa-Ca) and the L-type calcium current (ICa), in ventricular myocytes isolated from streptozotocin-induced diabetic rats. Recordings were made using the nystatin-perforated patch technique which minimizes interference with the normal intracellular Ca2+ buffering mechanisms. The averaged INa-Ca current density elicited by Ca2+ current was smaller in diabetic than in normal myocytes at all potentials tested. INa-Ca activated by rapid application of caffeine was significantly reduced and the decay phase was prolonged. The density of ICa was also significantly reduced by diabetes in the range of test potentials between -10 and +50 mV. In addition, the fast time constant of ICa inactivation, which represents mainly the sarcoplasmic reticulum (SR) Ca2+ release-induced inactivation, was significantly higher in diabetic than in normal myocytes. The decrease in ICa, which is the main source of trigger Ca2+ for SR Ca2+ release, may explain the significantly lowered peak systolic [Ca2+]i previously shown in diabetic myocytes. As activation of ICa is essential for subsequent stimulation of INa-Ca, reduced ICa may contribute to decreasing activation of the Na+-Ca2+ exchanger.

Animals↗
PubMed1998

Ionic and metabolic imbalance as potential factors of ischemia reperfusion injury.

This study examined the influence of metabolic substrates on the effects of trimetazidine on functional and metabolic aspects of the ischemic reperfused heart. Isovolumic rat hearts were submitted to a 30-minute period of global mild ischemia (coronary flow decreased by an average of 70%) and then reperfused at constant preischemic coronary flow rate. Either glucose (11 mM) or glucose and palmitic acid (0.1 mM) were used as metabolic substrates. Trimetazidine (6 x 10(-7)M) markedly reduced the increase in diastolic pressure that occurred on reperfusion after the ischemic episode, whatever the exogenous substrate used. However, in those hearts that received fatty acid, the postischemic increase in diastolic pressure was abolished. Ischemia-induced increase in acyl carnitine levels-determined as indicators of fatty acid utilization by myocardial cells-was significantly decreased by trimetazidine in those hearts receiving fatty acid. Also, similar effects to those of trimetazidine on the postischemic increase in diastolic pressure and on tissue levels of acyl carnitine were obtained in the presence of dichloroacetate. Moreover, the presence of trimetazidine was associated with a reduction in the intracellular pH decrease during ischemia in those hearts receiving fatty acid. Combined with previous studies, these results suggest that an improved metabolic balance by trimetazidine may well consequently decrease the ionic imbalance after a transient period of ischemia.

Acetylcarnitine↗
PubMed1997

Controversies on the sensitivity of the diabetic heart to ischemic injury: the sensitivity of the diabetic heart to ischemic injury is decreased.

Controversy exists as to whether the diabetic heart is more or less sensitive to ischemic injury. Although a considerable number of experimental studies have directly determined the effects of ischemia on the diabetic heart, there is still no general agreement as to whether metabolic changes within the myocardium contribute to the severity of ischemic injury. This paper reviews the evidence suggesting that the diabetic heart can actually be less sensitive to an episode of severe ischemia. Possible reasons for this decreased sensitivity to injury are discussed, which include a decreased accumulation of glycolytic products during ischemia (lactate and protons), as well as alterations in the regulation of intracellular pH in the diabetic heart. Based on existing studies, we suggest that although impaired glucose metabolism in the diabetic heart contributes to injury in hypoxic hearts or in hearts subjected to low-flow ischemia, diabetes-induced decreases in glycolysis can actually be beneficial to the diabetic heart during and following a severe ischemic episode. A decreased clearance of protons via the Na+/H+ exchanger may also contribute to the decreased sensitivity to ischemic injury in the diabetic heart.

Animals↗
PubMed1997

HCO3(-)-dependent alkalinizing transporter in adult rat ventricular myocytes: characterization and modulation.

The present work was designed to identify the HCO3(-)-dependent alkalinizing carrier in ventricular myocytes of normal and diabetic adult rats and to determine to what extent this system contributes to acid-equivalent extrusion after an intracellular acidification. We also examined the possible influence of intracellular Ca2+ (Cai2-) and glycolytic inhibition on the carrier activation. Intracellular pH (pHi) was recorded using seminaphthorhodafluor-1. The NH4+ method was used to induce an intracellular acid load. Evidence is provided for the existence of a Cl(-)-independent Na(+)-HCO3- cotransport contributing to pHi recovery from an intracellular acid load in ventricular cells of adult rats. Na(+)-HCO3- cotransport accounts for 33% of the total acid-equivalent efflux (JHe) from normal adult myocytes after intracellular acidification at pHi 6.75 in CO2/HCO3(-)-buffered solution. In addition, the activity of this carrier, which is not affected either by decreasing Cai2+ or by inhibiting Ca2+/calmodulin protein kinase II, is down-regulated by inhibition of glycolysis. Under pathophysiological conditions such as diabetes, although total JHe was significantly decreased compared with normal myocytes, JHe carried by Na(+)-HCO3- cotransport remained unchanged. However, because of a decrease in Na+/H+ exchange, the contribution of this carrier to total JHe increased with decreasing pHi (i.e., under conditions that may be associated with an ischemic episode), reaching approximately 58% of total JHe at pHi 6.75 (vs. approximately 33% in normal myocytes.

Amiloride↗
PubMed1997

Modulation by pH0 and intracellular Ca2+ of Na(+)-H+ exchange in diabetic rat isolated ventricular myocytes.

We have previously shown that diabetes is associated with a decrease in Na(+)-H+ exchange activity in rat cardiac papillary muscle. The present work has been carried out in order to elucidate the factors responsible for such an alteration. Thus, we have studied the effects of pH0 and intracellular Ca2+ on Na(+)-H+ exchange in ventricular myocytes isolated from streptozotocin-induced diabetic rat hearts. pH1 was recorded using carboxy-seminaphthorhodafluor (SNARF-1). The NH4+ (10 mmol/L) prepulse method was used to induce an acid load in order to activate Na(+)-H+ exchange in HEPES-buffered Tyrode's solution. Whereas diabetes did not change intracellular buffering power, it significantly decreased acid efflux through Na(+)-H+ exchange (acid efflux, 4.32 +/- 0.4 [n = 32, normal cells] versus 2.5 +/- 0.2 [n = 43, diabetic cells] meq/L per minute at pHi 6.9; P < .02). Upon changes of pH0 (at a range of 8.0 to 6.8), acid efflux similarly varied in normal and diabetic cells, thus pointing to an unchanged pH0 sensitivity of Na(+)-H+ exchange. Buffering of intracellular Ca2+ by pretreatment of the cells with BAPTA-AM (25 mumol/L Ca2(+)-chelator) resulted in a decrease by approximately 58% of acid efflux in the diabetic group. This decrease was even more marked in normal cells (by approximately 74%). Interestingly, the pH1 dependence of the acid efflux carried by Na(+)-H+ exchange then became identical in both groups of cells, thus pointing to a role for intracellular Ca2+ in the diabetes-related alterations of the exchange. Inhibition of calmodulin (by 1.5 mumol/L calmidazolium) and of Ca2+/calmodulin-dependent protein kinase II (by 2 mumol/L 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazin e [KN-62]) significantly slowed down pH1 recovery in both normal and diabetic cells. However, the effect of KN-62 was significantly lower in diabetic cells (efflux decreased by approximately 17%) compared with normal cells (decrease by 45%). In conclusion, these data, in light of recent observations showing a decreased [Ca2+]i associated with diabetes in isolated ventricular myocytes, suggest that changes in intracellular Ca2+ may play an important role in altering Na(+)-H+ exchange activity in diabetic ventricular myocytes. They also point to diabetes-related alterations in the Ca2+/calmodulin protein kinase II-dependent phosphorylation of Na(+)-H+ exchange.

Animals↗
PubMed1996

Intracellular pH control mechanisms in the diabetic myocardium.

Intracellular pH (pHi) regulation and the consequences of this regulation may play a crucial role during ischaemia and especially on reperfusion after an ischaemic episode. A significant decrease in Na+/H+ exchange activity was first demonstrated in papillary muscles isolated from hearts of diabetic rats, and recently confirmed in diabetic rat isolated ventricular myocytes. This depressed activity of one of the major pHi regulatory mechanisms may afford some protection against ischaemia/reperfusion injury. A protection was indeed observed in perfused hearts isolated from diabetic rats, in which there was a markedly improved recovery of contractility following ischaemia, comparable to that obtained with a pharmacological block of Na+/H+ exchange in normal hearts. This was associated with a markedly slower pHi recovery.

Animals↗
PubMed1996

Effects of S20787 on pHi-regulating mechanisms in isolated rat ventricular myocytes.

Intracellular pH (pHi) regulation in the heart relies on the activity of three membrane mechanisms: the Na+/H+ exchange and an Na+, HCO3(-)-dependent transport, both activated after an acid load, and the Cl-/HCO(3-) exchange, activated by an intracellular alkalinization. Whereas several specific inhibitors of Na+/H+ exchange exist, distinguishing between the two HCO3(-)-dependent mechanisms remains difficult, especially near the steady state, because of the lack of specific inhibitors. To detect one such inhibitor, we tested the effects of S20787 on pHi regulation in the rat isolated ventricular myocytes. Intracellular pH was recorded with the fluorescent probe carboxy-SNARF-1. The NH4Cl (10 mM) prepulse method was used to induce an acid load to activate the dual acid extrusion system; Cl-/HCO3- exchange was activated with the acetate (40 mM) prepulse method. Our results showed that (a) a high dose (5.10(-6) M) of S20787 did not change intracellular intrinsic buffering power, beta i; (b) the dual acid extrusion system was unaffected by S20787 in the concentration range of 10(-11)-10(-6) M; and (c) S20787 partially inhibited (approximately 50%) the activity of Cl-/HCO3- exchange in a dose-dependent manner, with an IC50 of 8.8 x 10(-10) M. This inhibitory action of S20787 did not change the steady-state pHi after 5-10 min application. Our results demonstrate that S20787 is a specific and potent partial inhibitor of Cl-/HCO3- exchange in cardiac cells.

Acid-Base Equilibrium↗
PubMed1996

Effects of trimetazidine on pHi regulation in the rat isolated ventricular myocyte.

1. We have examined the effects of trimetazidine (TMZ) on intracellular pH (pHi) regulation in rat isolated ventricular myocytes. pHi was recorded ratiometrically by use of the pH-sensitive fluoroprobe, carboxy-SNARF-1 (carboxy-seminaphtorhodafluor). 2. Following an intracellular acid load (induced by 10 mM NH4Cl removal), pHi recovery in HEPES-buffered Tyrode solution was significantly slowed down upon application of 0.3 mM TMZ only when myocytes were pretreated for 5 h 30 min (slowing by approximately 50%; P < 0.01). This effect of TMZ on pHi recovery was shown to be not only time- but also dose-dependent with a large, quickly reversible, effect obtained with 1 mM TMZ applied for 2-3 h (slowing by approximately 64%; P < 0.001). This slowing of pHi recovery was also associated with a decrease of the NH4+ removal-induced acidification. 3. Relationship between intracellular intrinsic buffering power (beta i) and pHi was assessed in absence or presence of TMZ (0.3 mM or 1 mM). As expected, beta i increased roughly linearly with a decrease in pHi in all cases. However, both concentrations of TMZ significantly increased beta i (by approximately 55 and 65% at pHi 7.1, respectively). 4. When Na+/H+ exchange was inhibited by dimethyl amiloride (DMA; 40 microM), trimetazidine (1 mM) did not change the H+ flux estimated at pHi 7.1 (0.31 +/- 0.03 mequiv l-1 min-1, n = 5, control, versus 0.30 +/- 0.025 mequiv l-1 min-1, n = 5, TMZ), ruling out any effect of TMZ on background acid loading. 5. Acid efflux carried by Na+/H+ exchange was significantly decreased only when myocytes were pretreated with 1 mM TMZ, for 2-3 h (JeH = 2.86 +/- 0.38 mequiv l-1 min-1, n = 26, control, versus 1.66 +/- 0.26 mequiv l-1 min-1, n = 10, TMZ, estimated at pHi 7.1; P < 0.05). 6. In conclusion, the present work demonstrates that, following an intracellular acid load in HEPES-buffered medium, trimetazidine slows down pHi recovery in rat isolated ventricular myocytes, primarily through an increase of beta i. An effect on Na+/H+ exchange is also detected but only after long-term incubation of the myocytes with TMZ.

Animals↗
PubMed1996

Altered Ca2+ handling in ventricular myocytes isolated from diabetic rats.

It has been suggested that alterations in intracellular Ca2+ homeostasis may be responsible for the development of diabetic cardiomyopathy. We have studied the effects of streptozotocin-induced diabetes on intracellular Ca2+ concentration ([Ca2+]i) in enzymically isolated rat ventricular myocytes. [Ca2+]i was measured using indo 1 or fluo 3. Both diastolic and peak systolic [Ca2+]i were reduced in diabetic compared with normal myocytes (by 52 and 43%, respectively). The decay phase of the systolic [Ca2+]i transient was slower in the diabetic myocyte compared with normal (time constant = 89.6 +/- 3.4 ms, n = 23, normal vs. 105.2 +/- 4.05 ms, n = 20, diabetic; P < 0.01). This led to a significant prolongation of the [Ca2+]i transient duration in the diabetic myocyte. In both normal and diabetic myocytes, increasing the frequency of electrical stimulation decreased peak systolic [Ca2+]i. The relationship between stimulation frequency and normalized peak systolic [Ca2+]i was the same for both normal and diabetic myocytes. We also found that the caffeine-induced Ca2+ release [used as an index of sarcoplasmic reticulum (SR) Ca2+ content] was significantly reduced in diabetic myocytes. These data indicate that SR Ca2+ content is decreased by diabetes. In the presence of thapsigargin (2.5 microM, an inhibitor of SR Ca(2+)-adenosinetriphosphatase), the magnitude and time course of stimulus-evoked [Ca2+]i transients were identical in both groups of myocytes, suggesting that Ca2+ influx and/or efflux across the plasma membrane is not significantly affected in diabetes. We conclude that 1) diabetes is associated with significant alterations in [Ca2+]i homeostasis and 2) the decrease in systolic [Ca2+]i and lengthening of the systolic [Ca2+]i transient result primarily from dysfunction of the SR.

Aniline Compounds↗
PubMed1995

Mechanisms of intracellular pH regulation during postischemic reperfusion of diabetic rat hearts.

A marked decrease in the activity of the amiloride-sensitive Na+/H+ exchanger has been demonstrated in hearts from streptozotocin (STZ)-induced diabetic rats. The aim of this study was to investigate the contribution of other specific sarcolemmal transport mechanisms to intracellular pH (pHi) recovery upon reperfusion in STZ-induced diabetic rat hearts and their relation to recovery of ventricular function. Isovolumic rat hearts were submitted to a zero-flow ischemic period of 28 min at 37 degrees C and then reperfused for 28 min. The time course of pHi decline during ischemia and of recovery on reperfusion was followed by means of 31P-labeled NMR. The perfusion buffers used were either HEPES or CO2/HCO3-. An HCO3(-)-dependent (amiloride-insensitive) mechanism contributed to pHi recovery after ischemia in the diabetic rat hearts. Even when the Na+/H+ exchanger was blocked by amiloride in nominally HCO3(-)-free solution, a rapid rise in pHi occurred during the first 3 min of reperfusion. The early rise in pHi was reduced by external lactate and inhibited by alpha-cyano-4-hydroxycinnamate. This suggested that a coupled H(+)-lactate efflux may be a major mechanism for acid extrusion in the initial stage of reperfusion. The observation of a higher functional recovery on reperfusion in diabetic hearts is in accordance with previous studies using HCO3- buffer. However, this study shows that a good recovery of function occurred even more rapidly in diabetic hearts receiving HEPES-buffered solution than in those receiving HCO3(-)-buffered solution. This suggests that the HCO3(-)-dependent mechanism of regulation may be depressed in diabetic rat hearts.

Amiloride↗
PubMed1994

Comparison of effects of aprikalim and of hypoxic and ischaemic preconditioning on extracellular potassium accumulation, metabolism, and functional recovery of the globally ischaemic rat heart.

OBJECTIVE: The aim was to compare the effects of a potassium channel opener, aprikalim, and of hypoxic and ischaemic preconditioning on extracellular K+ concentration change, metabolism, and ventricular function in isolated globally ischaemic rat hearts. METHODS: Isovolumetric rat hearts (37 degrees C) were treated with 1 microM (apri 1) or 30 microM (apri 30) aprikalim, or preconditioned with either 10 min of hypoxia (N2PC) or 5 min of ischaemia followed by 5 min of perfusion (IPC5) or 10 min of ischaemia followed by 3 min of perfusion (IPC10). Control hearts received neither treatment nor preconditioning. All hearts received 30 min of sustained ischaemia followed by 25 min of reperfusion. Extracellular K+ concentration was measured with a potassium sensitive electrode inserted into the extracellular space of the left ventricular wall. RESULTS: Recovery of left ventricular developed pressure after 25 min of reperfusion was only 19.20(SEM 5.09)% of the preischaemic level in the control group. No recovery was obtained for the apri 1 group. In contrast, a very good recovery was obtained for the apri 30 group [96.69(10.92)%], the N2PC group [104.92(17.40)%], and the IPC10 group [84.96(9.86)%]. The IPC5 group, however, did not have improved recovery of left ventricular pressure [14.15(5.61)%]; this is likely to be related to differences in the stimulation of anaerobic glycolysis. The protection was also markedly attenuated by pretreatment with 50 microM glibenclamide in the apri 30, N2PC, and IPC10 groups [22.76(9.00), 66.06(6.09), and 46.18(7.06)%, respectively]. Hearts treated with aprikalim before inducing ischaemia showed a concentration dependent increase in [K+]e. Hypoxic (N2PC) and ischaemic preconditioning (IPC5 and IPC10) were also associated with an increase in [K+]e over the 5-10 min period preceding the 30 min of sustained ischaemia. During sustained ischaemia all groups showed a nearly triphasic pattern of extracellular K+ changes with an early rising phase, with the exception of the N2PC group for which the early [K+]e rise was barely detectable. CONCLUSIONS: An increase in [K+]e before sustained ischaemia is one of the mechanisms involved in the conditions affording protection. Although important, this is not sufficient, and further protection may be accomplished by decreased stimulation of anaerobic glycolysis during the sustained ischaemia.

Animals↗
PubMed1993

Skinned cardiac fibres of diabetic rats: contractile activation and effects of 2,3-butanedione monoxime (BDM) and caffeine.

OBJECTIVE: The aim was to examine contractile properties of skinned cardiac fibres from rats with streptozotocin induced diabetes and to compare the effects of two agents, caffeine and 2,3-butanedione monoxime (BDM), on myocardial contractile characteristics of normal and diabetic cardiac fibres. METHODS: Small fibre bundles dissected from papillary muscles of the left ventricle were chemically skinned by exposure to Triton X-100. The tension-pCa (pCa = -log10 [Ca2+]) relationships were determined under isometric conditions. RESULTS: In skinned fibres from diabetic rats maximum Ca2+ activated force was unchanged in comparison with normal rats, but a significant, though small, increase in the Ca2+ sensitivity [pCa for one half maximal activation (pCa50)] of contraction was shown. Caffeine (5-20 mM) increased Ca2+ sensitivity in a dose dependent manner and to the same extent in the two groups of preparations. Up to 10 mM caffeine, maximum force was not affected. On the other hand, BDM (2 and 5 mM) decreased Ca2+ sensitivity in both normal and diabetic fibres, but the rightward shift of the tension-pCa relationship induced by BDM was more pronounced in diabetic than in normal fibres: pCa50 was 5.55(SEM 0.02), 5.51(0.01), and 5.46(0.01) in normal fibres, and 5.62(0.01), 5.51(0.02), and 5.45(0.02) in diabetic fibres for 0, 2, and 5 mM BDM, respectively. Maximum tension was similarly decreased by BDM in the two groups of fibres. CONCLUSIONS: (1) No change is induced by diabetes in the site of action of caffeine; (2) some drugs that affect myofilament Ca2+ sensitivity, such as BDM, may act differently in diabetic and control myocardium.

Animals↗