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Effects of DL-sotalol on action potential duration in single guinea-pig ventricular myocytes
J Mel
CM
Cardiol
23 (Supplement
IV)
(1991)
1 REVERSAL
OF IMIPRAMINE-INDUCED v max DEPRESSION IN GUINEA-PIG VENTRICULAR CELLS BY SODIUM LACTATE. M.M. Adamantidis, C.A. Adnet-Bonte, P.J. Adnet, B.A. Dupuis. Laborntoire de Pbarmacologie, FacultC de Medeciue, Lille, France. Imipramine intoxication often results in severe ventricular arrhythmias which can be reversed by sodium lactate administration. The mechanisms of Na lactate action remain unclear. This study was designed lo test (i) whether Na lactate can in vitro reverse the depression of maximal rate of depolarization (Vmax) induced by imipramine in guinea-pig ventricular cells, (ii) whether increased Na concentration [C] is the major contributor to the reversal effect of Na lactate and (iii) wbether alkalinisation or anion per se may play an important role. Action potentials were recorded using standard microelectrodes. The effects of increasing [Cl (1 to 100 mM) of either Na lactate, bicarbonate or chloride on Vmax were tested in preparations exposed or not to 10 PM imipramine (I). The influences of pH (7.35 or 7.50) and osmolarity (+ 2 to 200 mM sucrose) were also evaluated. 30 mM Na lactate, bicarbonate or chloride totally reversed the 25 % Vmax depression induced by I at pIi 7.50. This reversal effect was already obvious with the clinically relevant [C] of IO mM Na lactate and bicarbonate but not chloride. Imipramine effects developed more slowly at pH 7.50 than at pH 7.35 but did not differ after 90 minutes of exposure. Osmolarity did not reverse the I-induced Vmax depression. The results show that the increased Na [Cl seems to be the major contributor to the reversal effects of Na salts. However lactate and bicarbonate anions per se are important and more effective than chloride anions. These observations are consistent with the clinical use of Na lactate and bicarbonate in the treatment of imipramine intoxication.
2
EFFECTS OF DL-SOTALOL ON ACTION POTENTIAL DURATION IN SINGLE GUINEA-PIG VENTRICULAR MYOCYTES. M.M. Adamantidis, S. Kacet, P. Navarre, B. Dupuis. Laboratoire de Pbarmacologie, Facult6 de Medecine, Lille, France. DL-sotalol is a beta-blocking drug with additional class III antiarrhytbmic action and arrhythmogenic properties that have not been demonstrated in single cells. The aim of this study was (i) to investigate in single ventricular myocytes isolated by enzymatic dissociation from guinea-pig hearts. the effects of increasing concentrations [C] (0.3 to 100 PM) of DL-sotalol on action potential duration (APD) and the influence of stimulation frequency, extracellular K+ ICI and temperature, (ii) to evaluate the influence of DL-sotalol on depolarization-induced Action potentials were recorded using standard abnormalities (DIA) in repolarization. microelectrode techniques. [Cl-and frequency (1 to 150 pulses/minute)-dependent effects of DLsotalol were examined in normal (5.4 mM K+, 35”C), low K+ (2.7 mM, 35°C) and low temperature (5.4 mM K+p 22’C) Tyrode’s solution. As described in multicellular preparations, DL-sotalol caused a [Cl-dependent increase in APD in single ventricular cells stimulated at 60 pulses/minute (+ 25 W increase in APD at 90 W repolarization in 5.4 mM K+, 35°C medium at the [Cl of 100 HIM). At this latter [Cl, the APD lengthening is majored at final repolarization by low frequencies (1 to 30 pulses/minute), low temperature and low K+ solution whereas at plateau level, it was rather suppressed by low K+ solution. Injection of depolarizing currents (2 nAf induced DIA in normal cells. Exposure to DL-sotalol (100 wM) needed lower currents (1.2 nA in 5.4 mM K+, 0.02 nA in 2.7 mM K+) to elicit DIA. These results are consistent with the effects of DL-sotalol described in multicellular preparations and may be attributed to the reduction of the time-dependent K+ outward current (IK) and of the background K+ current (Ii(l).
3
EFFECTS OF FREE AND BOUND CALCIUM ON MITOCHONDRIAL RESPIRATION. M. Akioud, M. Constantln, A. Younes, R. Massingham. RL-CERM, Riom, France. It is well known that mitochondrial function is altered by calcium accumulat1on. As far as we know this was observed as a function of free calcium concentraOur purpose was to study whether the amount of tion in the surrounding medium. bound calcium had any influence on these alterations. Rat heart mitochondrla were incubated at 25OC. Jhe medium was buffered at pH 7,2 or pH 6,5 free and bound calcium (lo-BM - IOM) were calculated from the different EGTA concentrations according to the equations of Sillen and Martell (1971). State 3 and State 4 respiratory rates were measured with a Clark electrode I” presence of glutamate + malate (5 PM) as++oxida+t+ive substrate. Oxygen consumption at state 3 decreased depending on free Ca (Ca f& as ~$11 as bound calcium (Cab). At 10 mM Cab; state 3 rate decreased by 50% at 10 M Ca f (IC50). This IC50 increase with ecreasing bo+u+nd calcium; for instance at 0,l mM Cab the IC50 was around -2 2.10 M of6free+C+a . At 10 mM Cab oxygen consumption at state 4 showed an increase at -i,5.:2 M Ca f, nevertheless at 0,i mM Cab this increase was ob;$ined around IO Ca f. From above it is apparent that at physiological free Ca concentrations, mitochondrial respiratory rate and phosphorylation activity depend rather upon the amount of bound calcium.
S.l
CM
Cardiol
23 (Supplement
IV)
(1991)
1 REVERSAL
OF IMIPRAMINE-INDUCED v max DEPRESSION IN GUINEA-PIG VENTRICULAR CELLS BY SODIUM LACTATE. M.M. Adamantidis, C.A. Adnet-Bonte, P.J. Adnet, B.A. Dupuis. Laborntoire de Pbarmacologie, FacultC de Medeciue, Lille, France. Imipramine intoxication often results in severe ventricular arrhythmias which can be reversed by sodium lactate administration. The mechanisms of Na lactate action remain unclear. This study was designed lo test (i) whether Na lactate can in vitro reverse the depression of maximal rate of depolarization (Vmax) induced by imipramine in guinea-pig ventricular cells, (ii) whether increased Na concentration [C] is the major contributor to the reversal effect of Na lactate and (iii) wbether alkalinisation or anion per se may play an important role. Action potentials were recorded using standard microelectrodes. The effects of increasing [Cl (1 to 100 mM) of either Na lactate, bicarbonate or chloride on Vmax were tested in preparations exposed or not to 10 PM imipramine (I). The influences of pH (7.35 or 7.50) and osmolarity (+ 2 to 200 mM sucrose) were also evaluated. 30 mM Na lactate, bicarbonate or chloride totally reversed the 25 % Vmax depression induced by I at pIi 7.50. This reversal effect was already obvious with the clinically relevant [C] of IO mM Na lactate and bicarbonate but not chloride. Imipramine effects developed more slowly at pH 7.50 than at pH 7.35 but did not differ after 90 minutes of exposure. Osmolarity did not reverse the I-induced Vmax depression. The results show that the increased Na [Cl seems to be the major contributor to the reversal effects of Na salts. However lactate and bicarbonate anions per se are important and more effective than chloride anions. These observations are consistent with the clinical use of Na lactate and bicarbonate in the treatment of imipramine intoxication.
2
EFFECTS OF DL-SOTALOL ON ACTION POTENTIAL DURATION IN SINGLE GUINEA-PIG VENTRICULAR MYOCYTES. M.M. Adamantidis, S. Kacet, P. Navarre, B. Dupuis. Laboratoire de Pbarmacologie, Facult6 de Medecine, Lille, France. DL-sotalol is a beta-blocking drug with additional class III antiarrhytbmic action and arrhythmogenic properties that have not been demonstrated in single cells. The aim of this study was (i) to investigate in single ventricular myocytes isolated by enzymatic dissociation from guinea-pig hearts. the effects of increasing concentrations [C] (0.3 to 100 PM) of DL-sotalol on action potential duration (APD) and the influence of stimulation frequency, extracellular K+ ICI and temperature, (ii) to evaluate the influence of DL-sotalol on depolarization-induced Action potentials were recorded using standard abnormalities (DIA) in repolarization. microelectrode techniques. [Cl-and frequency (1 to 150 pulses/minute)-dependent effects of DLsotalol were examined in normal (5.4 mM K+, 35”C), low K+ (2.7 mM, 35°C) and low temperature (5.4 mM K+p 22’C) Tyrode’s solution. As described in multicellular preparations, DL-sotalol caused a [Cl-dependent increase in APD in single ventricular cells stimulated at 60 pulses/minute (+ 25 W increase in APD at 90 W repolarization in 5.4 mM K+, 35°C medium at the [Cl of 100 HIM). At this latter [Cl, the APD lengthening is majored at final repolarization by low frequencies (1 to 30 pulses/minute), low temperature and low K+ solution whereas at plateau level, it was rather suppressed by low K+ solution. Injection of depolarizing currents (2 nAf induced DIA in normal cells. Exposure to DL-sotalol (100 wM) needed lower currents (1.2 nA in 5.4 mM K+, 0.02 nA in 2.7 mM K+) to elicit DIA. These results are consistent with the effects of DL-sotalol described in multicellular preparations and may be attributed to the reduction of the time-dependent K+ outward current (IK) and of the background K+ current (Ii(l).
3
EFFECTS OF FREE AND BOUND CALCIUM ON MITOCHONDRIAL RESPIRATION. M. Akioud, M. Constantln, A. Younes, R. Massingham. RL-CERM, Riom, France. It is well known that mitochondrial function is altered by calcium accumulat1on. As far as we know this was observed as a function of free calcium concentraOur purpose was to study whether the amount of tion in the surrounding medium. bound calcium had any influence on these alterations. Rat heart mitochondrla were incubated at 25OC. Jhe medium was buffered at pH 7,2 or pH 6,5 free and bound calcium (lo-BM - IOM) were calculated from the different EGTA concentrations according to the equations of Sillen and Martell (1971). State 3 and State 4 respiratory rates were measured with a Clark electrode I” presence of glutamate + malate (5 PM) as++oxida+t+ive substrate. Oxygen consumption at state 3 decreased depending on free Ca (Ca f& as ~$11 as bound calcium (Cab). At 10 mM Cab; state 3 rate decreased by 50% at 10 M Ca f (IC50). This IC50 increase with ecreasing bo+u+nd calcium; for instance at 0,l mM Cab the IC50 was around -2 2.10 M of6free+C+a . At 10 mM Cab oxygen consumption at state 4 showed an increase at -i,5.:2 M Ca f, nevertheless at 0,i mM Cab this increase was ob;$ined around IO Ca f. From above it is apparent that at physiological free Ca concentrations, mitochondrial respiratory rate and phosphorylation activity depend rather upon the amount of bound calcium.
S.l