Effects of Disopyramide in HCM Cardiomyocytes
(Top) In HCM cardiomyocytes, ICa-L and INaL are increased, while IK is markedly decreased, leading to prolonged APs; Na overload impairs NCX, contributing to cytosolic Ca-overload. (Bottom) Disopyramide inhibits INa-peak (INaP), INaL, ICa-L and IK, while also stabilizing ryanodine receptors. These effects lead to shortening of APs. Moreover, normalization of NCX function and ICa-L inhibition and RyR stabilization contribute to reduce diastolic Ca and systolic Ca-release, determining negative inotropic effects.
APs = action potentials; HCM = hypertrophic cardiomyopathy; ICa-L = L-type Ca current; IK = delayed-rectifier K current; INaL = Late Na current; NCX = Na+/Ca2+ exchanger; RyR = ryanodine receptor.