Antiarrhythmic effects of a benzothiazine derivative (SD-3211) and its stereoisomer (SA3212) in anaesthetized rats and isolated perfused rat hearts compared with bepridil.

The antiarrhythmic effects of a new calcium channel blocking agent (SD-3211) and its stereoisomer with additional sodium channel blocking activity (SA3212), were compared with those of a known antiarrhythmic drug (bepridil), using the left coronary artery ligation- and reperfusion-associated arrhythmia models both in isolated rat hearts and in anaesthetized rats. Isolated and perfused rat hearts were subjected to regional ischaemia for 15 min and subsequent reperfusion for 5 min. SD-3211 and SA3212 showed dose-dependently prolongations of the time interval between coronary ligation and first appearance of ventricular premature beats, reductions in the number of total ventricular premature beats during the ligation period and reductions in the incidence of reperfusion-induced ventricular fibrillation. The values of the negative logarithm of IC50 (mol/l) of SD-3211, SA3212 and bepridil were 7.97, 7.41 and 6.64 for the reduction of ventricular premature beats during ligation and 6.43, 7.49 and 6.17 for the reduction of ventricular fibrillation during reperfusion, respectively. In a separate study on force of concentration and coronary flow in perfused heart paced at 340-360 beats/min SD-3211 caused a significant negative inotropic effect between 10(-7) and 10(-6) mol/l. SA3212 at the concentration of less than 10(-6) mol/l did not result in any significant change in force of contraction. The coronary flow was increased dose-dependently by SA3212, while it was first increased and then reduced in the presence of higher concentration of SD-3211 (greater than 10(-7) mol/l). Hearts of anesthetized rats were also subjected to regional ischaemia for 7 min and subsequent reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)