Abstract： Aim: To explore the effects of benactyzine (BEN) on the action potential and contractile force in guinea pig papillary muscles.Methods: Conventional microelectrode technique was used to record the fast action potentials (FAP) and slow action potentials (SAP) of guinea pig papillary muscles.Results: Benactyzine 5,10,50 μmol^. L^-1 suppressed the maximal upstroke velocity (v_max ) of FAP and contractile force (Fc) concentration-dependently while prolonged the action potential duration at 50%,90% repolarization (APD₅₀ ,APD₉₀ ) and effective refractory period (ERP) of FAP.The suppression on the v_max was frequency-dependent.Benactyzine 5,10,50μmol^. L^-1 lengthened the APD50,APD90 of SAP induced by isoprenaline or histamine when perfused with KCl 22 mmol^. L^-1 Tyrode's solution.The v_max of the SAP was not decreased by benactyzine 5,10 μmol^. L^-1 but by 50 μmol^. L^-1 .The effects on the SAP were antagonized by elevation of the extracellular calcium from 2.0 to 5.6 mmol^. L^-1 .The effects of benactyzine on SAP elicited by tetrodotoxin resembled that by isoprenaline or histamine except the more pronounced suppression on v_max and action potential amplitude (APA).The persistent rapid spontaneous activity and triggered tachyarrhythmia induced by ouabain were also abolished immediately by benactyzine 5 μmol^. L^-1 .Conclusion: Benactyzine can inhibit Na⁺ ,K⁺ ,Ca²⁺ transmembrane movement and intracellular Ca²⁺ mobilization in the myocardium,and this may be the electrophysiological basis of its effects against experimental arrhythmias.

INTRODUCTION

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