Protection by benzamil against dysfunction and damage in rat myocardium after calcium depletion and repletion

Perfusion of the rat right ventricular wall muscle for 4 min with a Ca2(+)-free medium followed by perfusion with a Ca2(+)-containing solution resulted in a 42% recovery of developed tension, contracture, and a massive release of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) from the muscle. High concentrations (1-5 mM) of amiloride partially protected the ventricular wall from Ca2+ paradox-induced dysfunction. The inclusion of benzamil, an amiloride analogue, 2 min before and during the Ca2(+)-free perfusion period prevented contracture development, restored force development, and almost totally eliminated the release of CPK and LDH from the muscle. Contractile function was best protected by 10-50 microM benzamil. The results demonstrate the efficacy of benzamil as a protective agent against Ca2+ paradox-induced myocardial dysfunction and damage. In view of the known capacity of benzamil to block transsarcolemmal Na(+)-Ca2+ exchange, this study supports the involvement of elevated intracellular Na+ and a stimulation of Na(+)-Ca2+ exchange in this model of cardiac pathology.