- Email: [email protected]
Ischaemia-induced electrophysiological changes in the pig in situ heart
J Mol
Cell
Cardiol
22 (Supplement
IV)
(1990)
73 IXHAEMIA-INDUCEDELWIROPHYSIOLOGICALCHANGES
IN THE PIG IN SITU HEART M.Freysz, J.F.Aupetit, I.Gerentes, J.Imfoua, Q.Ti.mur, G.Faucon Medical Phanmcology, Cl.Bemard University, F-69008 Lyon The effects of is&a&a produced by transient (2 to 5 mini occlusion of the left anterior descending coronary artery was studied in open-chest pigs by recording rronophasic action potential (MAP) in the ischaemic area using an appropriate electrade introduced into the ventricular wall thickness and fixed there. Study was performed with sinus rate to establish correspondence to the expected electrocardiographic changes affecting ST segments and T waves, but also under pacing to determine for a constant rate (180 bpn) depolarization velocity, conduction time and effective refractory period (EXP) in the ventricular contractile fibres. Ischaemia induces : 1) First at all, reduction in MAP duration due to anticipated and accelerated repolarization. 2) Decrease in MAP amplitude caused by both defect in repolarization and slming ~.CWI-Iwith insufficiency in depolarization. 3) In prefibrillatory period, substantial increase in conduction time and less pronounced decrease in EF@. All these changes are probably related to the reduction in active ion transfers,.conseqxnt upon the reduction in metabolic processes. According to the duration of occlusion, these changes disappear totally or partially when circulation is restored.
74
FORMATION OF GAP JUNCTIONS IN DEVELOPING MOUSE HEART. IMMUNOFLUORESCENCE INVESTIGATIONS. Fmrnaget C., El Aoumari A., Dupont E., Briand J.P. and Gros D. Lab. Biilogii de la DiMrenciation Cellulaire, LA CNRS 32, Marseille ; Lab. Immunochimie. LP CNRS 24, Strasbourg. Connexin 43 (CX43) is the major Protein of vertebrate car&c gap junctions. Antipeptide antibodies (Abs) raised in rabbit to a COOH-terminal domain (residues 314-322) of rat CX 43 were used to investigate the formation of gap junctions in mouse heart at different stagss of development. These Abs were previously shown to be specific for rat cardiac gap junctions by immuno-bldtii, - fluorescence and - electron microscoPy (El Aoumari et al., 1990, J. Membrane Biil., in Press). lmmunoblotting of whole embryonic, neonatal and adult mouse heart fractions show that CX 43 is detected from 14 dpc. Double immunofluorescence investigations were carried out with ventricle sections of frozen heart using fluorescein-labeled kctins (Con A or WGA. to mark cut the cell outlines) and rhcdamine-labeled GAR Abs. At 9 and 11 days post-coitum (dpc), tiny fluorescent dots are scattered in the ventricular wall and the trabearlae. At 14 dpc the small dots are more numercus and a gradient seems to form : the labelings are more frequent between the cells of the trabearlae than between the cells of the ventricular wall. At 16 dpc the gradient previously observed is more obviius and the labelings are homogeneously distributed at the periphery of rylrnemus cells. At 19 dpc the cells lengthened and they all show an homogeneous &ace labeling made of fluorescent dots and small dashes. In the 1 and 2 week post-parturn (wpp) new born hearts the fluorescence is seen both on the cell lateral sides and at the ends where the intercalated discs (ids) are differentiating. At 3 wpp the fluorescence is restricted to the ids and the closest lateral zones. At the adult stage (12 wpp) only the ids are labeled. (Supported by CNRS and INSERM). l
l
75
E;QUENCY DEPENDEN:? OF QT TyAL PROLONGATfON WlTy SOTAL?L IN v. g. Fuocke tano, Y. Kibleur, J.-M. Pomer, P. Jadlon. Chmcal Pharmacology Umt, StAntome Umverslty HospltaI, Pars, France. Animal studies have shown that drug-induced action potential prolongation increases with stow pacing rates. It has also beso suggested that the concentrations of sotalol (Sot) required for QT prolongation are 4 to 9 times higher than those required for 8-adrenoceptor blockade. In a randomized, crossover study of 3 dosages of Sot, we studied the rate dependence of its effects on ventricular repolarizatioo, measured as QT interval duration on the ECG, ia 10 normal volunteers. l-blockade (% reduction in peak exercise heart rate from control) was measured. During each period, 50 to 100 QT-RR pairs were measured over a wide range of RR intervals. In each subject, QTc, the QT interval normalized for a heart rate of 60 bpm, was calculated from the equation: QT=A-B*expx’%bicb best fit the QT vs. RR relationship. Sot-induced&blockade and QTc prolongation were dose- and coocentratioodependent (both pcO.01). The concentrations of Sot for which the 95% lower confidence interval of the relationship betweo &blockade or QTc prolongation and concentration rose above 0 were similar, 840 ag/ml and 680 &ml respectively. QT prolongation with Sot decreased with decreasing RR iotervals (i.e. increasing heart rate) at all dosages (figure). For example, at the dosage or &lCmg/Z-Zh, Sot increased QT by X6+4% (SD) at RR-6C0ms and by 11.8~3% at RR=1000 ms compared to control values (pcO.01) In conclusion: Sot prolongs QTc interval in man at dosages and concentrations simii to those required to produce b-adrenoceptor blockade; QTc prolongation with Sot is more pronounced when heart rate decreases; the latter result might contribute to explain the beneficial effect of heart rate acceleration in the treatment of Sot-induced torsade de pointes. S.25
Cell
Cardiol
22 (Supplement
IV)
(1990)
73 IXHAEMIA-INDUCEDELWIROPHYSIOLOGICALCHANGES
IN THE PIG IN SITU HEART M.Freysz, J.F.Aupetit, I.Gerentes, J.Imfoua, Q.Ti.mur, G.Faucon Medical Phanmcology, Cl.Bemard University, F-69008 Lyon The effects of is&a&a produced by transient (2 to 5 mini occlusion of the left anterior descending coronary artery was studied in open-chest pigs by recording rronophasic action potential (MAP) in the ischaemic area using an appropriate electrade introduced into the ventricular wall thickness and fixed there. Study was performed with sinus rate to establish correspondence to the expected electrocardiographic changes affecting ST segments and T waves, but also under pacing to determine for a constant rate (180 bpn) depolarization velocity, conduction time and effective refractory period (EXP) in the ventricular contractile fibres. Ischaemia induces : 1) First at all, reduction in MAP duration due to anticipated and accelerated repolarization. 2) Decrease in MAP amplitude caused by both defect in repolarization and slming ~.CWI-Iwith insufficiency in depolarization. 3) In prefibrillatory period, substantial increase in conduction time and less pronounced decrease in EF@. All these changes are probably related to the reduction in active ion transfers,.conseqxnt upon the reduction in metabolic processes. According to the duration of occlusion, these changes disappear totally or partially when circulation is restored.
74
FORMATION OF GAP JUNCTIONS IN DEVELOPING MOUSE HEART. IMMUNOFLUORESCENCE INVESTIGATIONS. Fmrnaget C., El Aoumari A., Dupont E., Briand J.P. and Gros D. Lab. Biilogii de la DiMrenciation Cellulaire, LA CNRS 32, Marseille ; Lab. Immunochimie. LP CNRS 24, Strasbourg. Connexin 43 (CX43) is the major Protein of vertebrate car&c gap junctions. Antipeptide antibodies (Abs) raised in rabbit to a COOH-terminal domain (residues 314-322) of rat CX 43 were used to investigate the formation of gap junctions in mouse heart at different stagss of development. These Abs were previously shown to be specific for rat cardiac gap junctions by immuno-bldtii, - fluorescence and - electron microscoPy (El Aoumari et al., 1990, J. Membrane Biil., in Press). lmmunoblotting of whole embryonic, neonatal and adult mouse heart fractions show that CX 43 is detected from 14 dpc. Double immunofluorescence investigations were carried out with ventricle sections of frozen heart using fluorescein-labeled kctins (Con A or WGA. to mark cut the cell outlines) and rhcdamine-labeled GAR Abs. At 9 and 11 days post-coitum (dpc), tiny fluorescent dots are scattered in the ventricular wall and the trabearlae. At 14 dpc the small dots are more numercus and a gradient seems to form : the labelings are more frequent between the cells of the trabearlae than between the cells of the ventricular wall. At 16 dpc the gradient previously observed is more obviius and the labelings are homogeneously distributed at the periphery of rylrnemus cells. At 19 dpc the cells lengthened and they all show an homogeneous &ace labeling made of fluorescent dots and small dashes. In the 1 and 2 week post-parturn (wpp) new born hearts the fluorescence is seen both on the cell lateral sides and at the ends where the intercalated discs (ids) are differentiating. At 3 wpp the fluorescence is restricted to the ids and the closest lateral zones. At the adult stage (12 wpp) only the ids are labeled. (Supported by CNRS and INSERM). l
l
75
E;QUENCY DEPENDEN:? OF QT TyAL PROLONGATfON WlTy SOTAL?L IN v. g. Fuocke tano, Y. Kibleur, J.-M. Pomer, P. Jadlon. Chmcal Pharmacology Umt, StAntome Umverslty HospltaI, Pars, France. Animal studies have shown that drug-induced action potential prolongation increases with stow pacing rates. It has also beso suggested that the concentrations of sotalol (Sot) required for QT prolongation are 4 to 9 times higher than those required for 8-adrenoceptor blockade. In a randomized, crossover study of 3 dosages of Sot, we studied the rate dependence of its effects on ventricular repolarizatioo, measured as QT interval duration on the ECG, ia 10 normal volunteers. l-blockade (% reduction in peak exercise heart rate from control) was measured. During each period, 50 to 100 QT-RR pairs were measured over a wide range of RR intervals. In each subject, QTc, the QT interval normalized for a heart rate of 60 bpm, was calculated from the equation: QT=A-B*expx’%bicb best fit the QT vs. RR relationship. Sot-induced&blockade and QTc prolongation were dose- and coocentratioodependent (both pcO.01). The concentrations of Sot for which the 95% lower confidence interval of the relationship betweo &blockade or QTc prolongation and concentration rose above 0 were similar, 840 ag/ml and 680 &ml respectively. QT prolongation with Sot decreased with decreasing RR iotervals (i.e. increasing heart rate) at all dosages (figure). For example, at the dosage or &lCmg/Z-Zh, Sot increased QT by X6+4% (SD) at RR-6C0ms and by 11.8~3% at RR=1000 ms compared to control values (pcO.01) In conclusion: Sot prolongs QTc interval in man at dosages and concentrations simii to those required to produce b-adrenoceptor blockade; QTc prolongation with Sot is more pronounced when heart rate decreases; the latter result might contribute to explain the beneficial effect of heart rate acceleration in the treatment of Sot-induced torsade de pointes. S.25