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M A Devynck

Publications and source records attributed to M A Devynck.

At least 55 records · Page 3Linked to original sources
PubMed1995

Alterations of cytosolic calcium in platelets and erythrocytes of Lyon hypertensive rats.

Platelet cytosolic free calcium concentration ([Ca2+]i) and intracellular pH (pHi) (including their responses to thrombin), as well as erythrocyte [Ca2+]i and 45Ca2+ influx, were studied in Lyon hypertensive (LH) and normotensive (LN) rats aged 3 months. Platelets of LH rats were characterized by substantially elevated basal [Ca2+]i values, higher [Ca2+]i levels after thrombin stimulation, and enhanced initial rate of thrombin-induced Mn2+ entry through receptor-operated Ca2+ channels. Basal platelet pHi values were not significantly different in LH and LN animals but thrombin elicited a significant alkalinization only in LH platelets. Erythrocytes of LH rats had an enhanced initial rate of 45Ca2+ and tended to elevated [Ca2+]i levels. Our data indicate profound alterations in cell Ca2+ handling in platelets and erythrocytes of LH rats, similar to those previously described in spontaneously hypertensive rats of the Okamoto-Aoki strain. The analysis of the relations between blood pressure, plasma lipids, and cell Ca2+ handling suggested that triglycerides, but not cholesterol, might be involved in altered platelet Ca2+ handling in LH rats.

Animals↗
PubMed1995

Different effects of endothelin-3 on the Ca2+ discharge induced by agonists and Ca(2+)-ATPase inhibitors in human platelets.

1. The present study demonstrates that endothelin-3 (ET-3), previously shown to attenuate thrombin-evoked aggregation of human platelets, delayed the dose-dependent aggregatory response to thapsigargin (Tg). As this Ca(2+)-ATPase inhibitor induces platelet activation in part through the depletion of internal Ca(2+)-stores, we examined the influence of ET-3 on Ca2+ discharge from internal pools. 2. Cytosolic Ca2+ concentration was evaluated with Fura-2 in the absence of Ca2+ influx. Platelet preincubation for 15 min with 5 x 10(-7) M ET-3 decreased the Ca2+ release evoked by thrombin and U46619, a thromboxane-mimetic. However, ET-3 did not affect Ca2+ movements induced by 1 microM ADP. Addition of Tg (0.5 to 5 microM) to resting platelets induced a cytosolic [Ca2+] rise with concentration-dependent increase of the initial rate and decrease of the time to reach the peak. ET-3 slowed down these dose-dependent effects with a more marked influence on the responses induced by low concentrations of Tg. 3. ET-3 did not modify the Ca2+ response to another Ca(2+)-ATPase inhibitor, 2,5-di-(tert-butyl)-1,4-benzohydroquinone(tBuBHQ). The thromboxane A2 receptor antagonist, SQ 29548, reduced by 53% the calcium signal evoked by 1 microM Tg, which became similar to that induced by 15 microM tBuBHQ. Under these conditions, the ET-3 effects were suppressed. A subsequent addition of thrombin induced a substantial further Ca2+ increase which was again sensitive to ET-3. 4. ET-3 attenuates Ca2+ mobilization from an internal pool dependent on the stimulation of thrombin and thromboxane A2 receptors and insensitive to the direct effect of Ca2+-ATPase inhibitors. The small but significant inhibitory effect of ET-3 leads us to propose that endothelin-3 acts as a modulator of platelet activation.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1995

Platelet cytosolic Ca2+ and membrane dynamics in patients with primary hypercholesterolemia. Effects of pravastatin.

This study was designed to evaluate the relationships between platelet cytosolic Ca2+ concentration ([Ca2+]i) and plasma lipids in patients with primary hypercholesterolemia. In a double-blind, placebo-controlled trial, we determined platelet [Ca2+]i in the presence and virtual absence of extracellular Ca2+ and the effects of prolonged treatment with pravastatin, a selective inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase. Platelet [Ca2+]i and membrane microviscosity were determined in 22 normotensive hypercholesterolemic men. Platelet [Ca2+]i was observed to vary with in vivo plasma lipid characteristics: in untreated patients, [Ca2+]i determined at low extracellular Ca2+ concentration was significantly associated with plasma triacylglycerols (P = .008) and with the total cholesterol to HDL cholesterol ratio (P = .044). Triacylglycerol levels also correlated inversely with the external Ca(2+)-dependent [Ca2+]i rise. Pravastatin treatment reduced plasma total cholesterol (-20 +/- 3%), LDL cholesterol (-30 +/- 3%), triacylglycerols (-17 +/- 6%), and apoB levels (-25 +/- 4%) and simultaneously decreased platelet [Ca2+]i measured in a low-Ca2+ medium by 14 +/- 6% (P = .03). However, [Ca2+]i values remained positively correlated with the total cholesterol to HDL cholesterol ratio (P = .04). Prvastatin treatment did not induce marked changes in membrane microviscosity, although the changes in trimethylaminodiphenylhexatriene anisotropy were inversely correlated with those of HDL cholesterol. These results indicate that plasma lipids can modulate cytosolic Ca2+ in platelets by affecting Ca2+ transport pathways that are dependent and independent of Ca2+ influx.

Adult↗
PubMed1995

Endothelin-3 decreases Ca2+ uptake in platelet membrane vesicles.

To analyze the mechanisms by which endothelin-3 (ET-3) attenuates agonist-mediated Ca2+ mobilization from an internal pool, we investigated ET-3 effects on 45Ca2+ uptake in platelet membrane vesicles. They were compared to those of thapsigargin (Tg), a specific inhibitor of the dense tubule Ca2+ pumps. In the absence of ATP, ET-3 up to 1 microM did not affect the amount of Ca2+ bound to membrane sites. In the presence of ATP, ET-3 dose-dependently reduced the initial rate and the extent of Ca2+ uptake (p < 0.001). In comparison, Tg dose-dependently inhibited both the ATP-independent Ca2+ binding (p < 0.001) and the ATP-dependent Ca2+ accumulation (p < 0.001), with half-maximal effects at 7 nM. Pretreatment with 1 microM ET-3 decreased the inhibitory effect of 10 nM Tg, but only on the initial rate of ATP-dependent Ca2+ uptake (p = 0.04; n = 6). These results indicate that ET-3 is functionally coupled to Ca(2+)-ATPases of the dense tubules. Its inhibitory effects are probably due to inhibition of the catalytic cycle of the Ca2+ pumps. Such inhibition could lead to a depletion of Ca2+ stores and therefore to reduced Ca2+ release in response to agonists.

Adenosine Triphosphate↗
PubMed1995

Platelet cytosolic calcium concentration, plasma lipids and hypertension.

OBJECTIVE: To study the relationship between high blood pressure and hyperlipidaemia and the cytosolic calcium concentration in unstimulated platelets, focusing on the effects of an alteration in membrane dynamics. MATERIALS AND METHODS: Basal cytosolic calcium concentrations were determined in the presence and the absence of a significant calcium influx in platelets of 47 untreated hypertensive patients and 26 normotensive subjects. Membrane microviscosity was investigated by fluorescence depolarization of diphenylhexatriene and trimethylaminodiphenylhexatriene. To study the influence of plasma factors, unstimulated platelets were loaded in the presence of plasma with Quin-2, which forms a relatively strong intracellular calcium buffer. The cytosolic calcium concentration was then determined at two extracellular calcium concentrations (1 mmol/l and in the absence of a Ca2+ influx). RESULTS: Irrespective of the external calcium concentration, the cytosolic calcium concentration increased significantly with diastolic blood pressure (P = 0.026 in the presence and P = 0.003 in the absence of Ca2+ influx) and with plasma triacylglycerols (P = 0.03 and 0.001, respectively). Multiple regression analysis indicated that the cytosolic Ca+ concentration was independently related to these two factors [Ca2+ = 35 + (18.6 +/- 4.6). In triacylglycerols (mmol/l) + (0.45 +/- 0.15) mmHg diastolic blood pressure; P < 0.001]. The relationship between the cytosolic calcium concentration and diphenylhexatriene or trimethylaminodiphenylhexatriene anisotropies was not independent of blood pressure and plasma triacylglycerol levels. CONCLUSIONS: The present results confirm the link between blood pressure and the platelet cytosolic calcium concentration and indicate that plasma triacylglycerols directly or indirectly modulate the ex vivo efficacy of platelet calcium storage and/or extrusion mechanisms. They could facilitate cell stimulation.

Blood Platelets↗
PubMed1994

Alterations of membrane properties in erythrocytes of salt hypertensive Sabra rats.

This study was designed to investigate the effects of a hypertensive stimulus, high salt intake, in hypertension-prone (SBH) and -resistant (SBN) Sabra rats on erythrocyte Na+ content (Na+i), Ca2+ influx and cytosolic Ca2+ concentration ([Ca2+]i). The relationships of these parameters to plasma lipids, circulating digoxin-like immunoreactivity and membrane microviscosity, determined by the fluorescence anisotropy of trimethylamino-diphenylhexatriene (TMA-DPH) and diphenylhexatriene (DPH), were also evaluated. Erythrocytes of SBH rats were characterized by increased [Ca2+]i, unchanged Ca2+ influx and reduced Na+i. There were no significant differences in the plasma digoxin-like immunoreactivity between the two strains. High-salt intake decreased membrane microviscosity (DPH anisotropy) in SBH rats but did not alter the above parameters. Erythrocyte [Ca2+]i correlated positively with diastolic blood pressure and negatively with erythrocyte Na+i. Membrane dynamics evaluated by the two fluorescent probes did not correlate with [Ca2+]i, Ca2+ influx or Na+i whereas DPH anisotropy was inversely related to blood pressure. These relationships were independent of plasma cholesterol or triglycerides. It can be concluded that 1) similarly to earlier observations in essential hypertension and spontaneously hypertensive rats, erythrocyte [Ca2+]i correlates positively with blood pressure in salt-dependent hypertension, and 2) increased erythrocyte Na+ content need not be a hallmark of hypertension.

Animals↗
PubMed1994

Erythrocyte Ca2+ handling in the spontaneously hypertensive rat, effect of vanadate ions.

Cytosolic Ca2+ concentration ([Ca2+]i) and 45Ca2+ influx were investigated in erythrocytes from conscious spontaneously hypertensive rats (SHR) and their normotensive controls Wistar-Kyoto (WKY). [Ca2+]i was evaluated with fura-2 and intra- and extra-cellular calibration parameters were compared. Irrespective of the calibration parameters used, erythrocyte [Ca2+]i was always significantly higher in SHR than in WKY and Wistar rats (by 25 and 40%, p < 0.01 and 0.001). A rise of the external Ca2+ concentration from 1 to 2 mmol/l increased less [Ca2+]i in SHR than in WKY erythrocytes (17 vs 37%, p < 0.01). SHR erythrocytes incorporated more 45Ca2+ than those from WKY, with an initial rate of 45Ca2+ uptake higher by 57% than that of WKY erythrocytes (p < 0.05). Vanadate ions, after corrections of their quenching effect on red cell and fura-2 fluorescence signals, increased [Ca2+]i by 19% in WKY erythrocytes (p = 0.05), but did not modify the SHR values. They also increased 45Ca2+ accumulation and the initial rate of 45Ca2+ influx in WKY erythrocytes only (p < 0.01). This study indicates that, when compared to WKY rats, erythrocytes from SHR are characterized by higher [Ca2+]i values, higher initial rate of Ca2+ influx and low sensitivity to vanadate ions.

Animals↗
PubMed1994

Platelet membrane microviscosity in Sabra rats with early salt hypertension.

1. To investigate the possibility that arterial hypertension is associated with changes in the physicochemical properties of cell membranes, we have studied the effects of dietary salt loading on platelet membrane microviscosity in hypertension-prone and -resistant Sabra rats. 2. Sixteen hypertension-prone and 14 hypertension-resistant Sabra rats were submitted to either a low-salt (0.25% NaCl) or a high-salt (4% NaCl) diet for 3-4 weeks. Platelet membrane anisotropy was determined, in the presence and absence of extracellular Na+, using two fluorescent probes, diphenylhexatriene and trimethylamino-diphenylhexatriene, inserted in different areas of the cell membranes. 3. A decrease in diphenylhexatriene anisotropy was demonstrated when platelets of hypertension-prone (but not hypertension-resistant) Sabra rats were suspended in a Na(+)-free medium. This alteration in membrane dynamic properties is localized within the hydrophobic core of the platelet membranes and is independent of salt intake. It reflects an abnormal fluidizing effect of extracellular Na+ removal. 4. Platelets of hypertension-prone and hypertension-resistant Sabra rats did not differ significantly in trimethylamino-diphenylhexatriene fluorescence anisotropy, irrespective of the incubation media used. Extracellular Na+ removal caused an increase in trimethylamino-diphenylhexatriene fluorescence anisotropy in all groups, the change being greatest in salt-loaded rats. 5. This study indicates that platelet membrane microviscosity is specifically altered in the hypertension-prone Sabra rat irrespective of salt intake. This raises the question of the relation of this inherited defect with the susceptibility of this strain to dietary salt loading.

Animals↗
PubMed1994

Platelet and erythrocyte membrane microviscosity in Lyon hypertensive rats.

The altered membrane microviscosity demonstrated in various cells of spontaneously hypertensive rats (SHR) and essential hypertensive (EH) patients has been proposed to play an important role in the pathogenesis of genetic forms of hypertension. The aim of this study was to evaluate possible changes of membrane microviscosity in platelets and red cell ghosts of Lyon hypertensive (LH) and normotensive (LN) rats. Both erythrocyte and platelet membranes of LH rats had a clear tendency to reduced DPH fluorescence anisotropy reflecting the decreased core membrane microviscosity. On the other hand, there were no changes in TMA-DPH fluorescence anisotropy that characterizes the dynamic properties of the outer membrane leaflet. DPH, but not TMA-DPH, anisotropy correlated negatively with blood pressure. This was true for both red cell ghosts and platelets. Membrane microviscosity had no significant relationship to plasma cholesterol or triglycerides. In platelets, TMA-DPH anisotropy correlated positively with cytosolic free calcium concentration ([Ca2+]i). A similar trend was observed in erythrocytes. In contrast, DPH anisotropy had an inverse relationship to platelet [Ca2+]i. It can be concluded that the alterations of membrane microviscosity seen in LH rats are completely different from those reported in SHR animals and that surface and core membrane microviscosity differ in their relationship to blood pressure and [Ca2+]i.

Animals↗
PubMed1994

Inhibitory effect of trimetazidine on thrombin-induced aggregation and calcium entry into human platelets.

The antiaggregatory properties of trimetazidine were investigated further by analyzing its effects on cytosolic calcium and proton concentrations, well-known regulators of platelet reactivity. Aggregatory responses of washed platelets were assessed by turbidometry, and cytosolic Ca2+ concentration ([Ca2+]i) and pH (pHi) were determined by their respective fluorescent probes: Fura-2 and BCECF. Preincubation with trimetazidine dose-dependently inhibited platelet aggregation induced by 0.05 U/ml thrombin (p < 0.001). At concentrations < or = 1 mM, trimetazidine did not affect the resting [Ca2+]i value but slightly alkalinized the cytosol by 0.05 +/- 0.03 pH units (p < 0.02, n = 11). In platelets stimulated by 0.05 U/ml thrombin, 0.1 mM trimetazidine did not modify pHi variations but decreased [Ca2+]i variations (p < 0.003, n = 16), blunting by 28 +/- 6% the transient peak of [Ca2+]i (p < 0.006) and decreasing by 6 +/- 2% the equilibrium value (p < 0.005). These inhibitory effects were inversely dependent on thrombin concentrations (p < 0.004, n = 21) and were abolished in the virtual absence of external Ca2+. Trimetazidine therefore attenuates the Ca2+ influx evoked by thrombin, thereby limiting Ca2+ accumulation in stimulated platelets. Such a protective effect may participate in the antiaggregatory properties of trimetazidine.

Blood Platelets↗
PubMed1994

Erythrocyte membrane microviscosity and blood pressure in rats with salt-induced and spontaneous hypertension.

OBJECTIVE: To study membrane viscosity in various rat strains with genetic forms of experimental hypertension. DESIGN: The relationship between blood pressure and membrane dynamics was investigated in erythrocytes from three different rat strains with experimental hypertension, namely two models of salt-induced hypertension (Sabra and Dahl rats) and Lyon hypertensive rats with spontaneous hypertension. METHODS: Membrane microviscosity was evaluated by diphenylhexatriene and trimethylamino-diphenylhexatriene fluorescence steady-state anisotropy. RESULTS: There were no significant differences among particular experimental groups in trimethylamino-diphenylhexatriene anisotropy that reflect microviscosity changes at the water-lipid interface of the external membrane leaflet. In contrast, the diphenylhexatriene anisotropy, which is related to the core membrane microviscosity, was significantly reduced in the Dahl salt-sensitive rats (irrespective of salt intake level) and in the Sabra hypertension-prone rats with developed salt hypertension. Erythrocyte membranes of Lyon hypertensive rats also had lower values of diphenylhexatriene anisotropy than the respective normotensive controls but this difference was not statistically significant. CONCLUSIONS: Systolic (and often also diastolic) blood pressure correlated negatively with the diphenylhexatriene anisotropy in each of the three strains studied, whereas the trimethylamino-diphenylhexatriene anisotropy of the erythrocyte membranes had no significant relationship to the blood pressure. Further experiments should clarify whether the observed relationship of the diphenylhexatriene anisotropy to blood pressure reflects true pathogenetic mechanisms or is a consequence of haemodynamic changes.

Animals↗
PubMed1994

Platelet aggregation and in vivo shear forces.

Haemodynamic shear forces have been reported to exert direct and indirect effects on platelet reactivity. In vitro, they activate platelets leading to spontaneous or facilitated aggregation. In vivo, they stimulate the production of endothelium-derived anti-aggregatory agents. This study was designed to evaluate in hypertensive patients, before and after antihypertensive treatment, the possible role of these haemodynamic forces, determined at the brachial artery level on the ex vivo platelet aggregatory response to ADP and collagen. Platelet reactivity, evaluated by EC50 for ADP and collagen, was found to be related to blood velocity, shear rate and shear stress (p < 0.01 for each). These inverse correlations of platelet aggregation with stress levels did not depend on age, body mass index, mean blood pressure, serum cholesterol and triglycerides or haematocrit. They were also independent of platelet cytosolic Ca2+ and cyclic AMP. The changes in shear forces and in aggregatory responses to ADP and collagen induced by nitrendipine treatment for 6 months remained negatively correlated, confirming the relationships existing between haemodynamic shear forces and platelet reactivity. These results indicate that the shear antiaggregant effects, likely mediated by flow-dependent endothelium-derived factors, prevail over its direct platelet aggregating effects.

Adenosine Diphosphate↗
PubMed1993

Acute membrane effects of trimetazidine in human platelets.

The mechanisms by which trimetazidine (1-[2,3,4-trimethoxybenzyl]-piperazine) exerts its cytoprotective action have not been identified. This study was designed to investigate in human platelets and erythrocyte ghosts a possible perturbation of membrane dynamics by trimetazidine. Its effects on the steady-state anisotropies of two fluorescent probes, trimethylamino-diphenyl-hexatriene (TMA-DPH) and diphenylhexatriene (DPH) were compared. The effects on the aggregatory responses to collagen and ADP, and on platelet cAMP content were also investigated. In platelets, trimetazidine dose-dependently raised TMA-DPH anisotropy but not that of DPH. It reduced cAMP content (in the presence of Ro 15-2041, a phosphodiesterase inhibitor) and the aggregation responses to collagen and ADP. This suggests that trimetazidine decreases the 'fluidity' of the outer part of the plasma membrane, the adenylyl cyclase activity and some steps involved in platelet activation. In erythrocyte ghosts, the fluorescence anisotropy of TMA-DPH was not modified by trimetazidine. The membrane effects reported here could participate in the protection of cell metabolism afforded by a long-term treatment with trimetazidine.

Adenosine Diphosphate↗
PubMed1993

Plasma lipids and platelet membrane fluidity in essential hypertension.

Essential hypertension is often associated with high levels of plasma cholesterol or triglycerides. The relationships between plasma lipids and platelet lipids, membrane fluidity and functions in untreated hypertensive patients were investigated by measuring the fluorescence anisotropies of two fluorescent dyes (DPH and its cationic derivative, TMA-DPH, with different subcellular localization), cytosolic Ca2+ and pH, cyclic AMP content and aggregation to ADP and collagen. Hypercholesterolemia was found to be accompanied by a rise in platelet cholesterol content without changes in TMA-DPH or DPH anisotropies whereas hypertriglyceridemia was associated with a decreased cholesterol to phospholipid molar ratio, a decreased DPH anisotropy and a tendency of the cytosol to alkalinize. These results point out the differences between the effects of an acute cholesterol load and those of chronic hypercholesterolemia on platelet membrane microviscosity and aggregation. They demonstrate a strong association between plasma triglyceride levels and platelet membrane structure.

Adult↗
PubMed1993

Regulation of the dynamic properties of platelet plasma membrane by intracellular sodium ions.

Our previous experiments in human and rat platelets demonstrated that the absence of extracellular Na+ increased the fluorescence anisotropy of TMA-DPH (trimethylamino-diphenylhexatriene, probe preferentially incorporated into the outer leaflet of the plasma membrane). Here we investigated further the in vitro effects of Na+ ions on membrane dynamic properties. Na(+)-dependent changes were reversible and they required about 10-20 min to be induced. They were specifically located in the TMA-DPH environment because they were not observed with diphenylhexatriene (probe non-selectively incorporated into all hydrophobic domains of the cell). To evaluate the possible influence of the intracellular Na+, the effects of sodium replenishment, monensin, ouabain and thrombin on TMA-DPH anisotropy were measured. A rise in intracellular Na+ above the physiological level was associated with unchanged or slightly decreased TMA-DPH anisotropy whereas its decrease was accompanied by a pronounced rise in TMA-DPH anisotropy. Our data indicate that the changes in intracellular Na+ concentration, rather than those in extracellular Na+ concentration, are responsible for the alterations in platelet membrane fluidity probed by TMA-DPH.

Animals↗
PubMed1993

In vivo shear flow and erythrocyte membrane fluidity in hypertensive patients.

1. To evaluate the response of red blood cells subjected to the shear flow in hypertension, the relationships between wall shear phenomena determined in vivo in the brachial artery of hypertensive patients and the modifications of the membrane dynamics measured in vitro in erythrocyte ghosts of 32 patients were investigated. 2. Two fluorescent probes, diphenylhexatriene (DPH) and its trimethylamino-derivative (TMA-DPH), localized respectively in the lipid membrane core and at the lipid-water interface, were used. 3. Shear rate, shear stress and blood velocity were positively correlated with TMA-DPH anisotropy (P = 0.015, 0.005 and 0.026, respectively), but not with that of DPH. This indicates that wall shear forces were associated with the microviscosity of the outer part of the cell membrane. 4. The changes in wall shear forces and erythrocyte membrane microviscosity probed by TMA-DPH or DPH were observed to vary in parallel under nitrendipine therapy. 5. These results suggest that in vivo shear forces participate in the control of erythrocyte membrane fluidity or that erythrocytes adapt their membrane properties to blood flow conditions.

Antihypertensive Agents↗