Modification of Distinct Ion Channels Differentially Modulates Ca Dynamics in Primary Cultured Rat Ventricular Cardiomyocytes

Primary cultured cardiomyocytes show spontaneous Ca oscillations (SCOs) which not only govern contractile events, but undergo derangements that promote arrhythmogenesis through Ca -dependent mechanism. We systematically examined influence on SCOs of an array of ion channel modifiers by recording intracellular Ca dynamics in rat ventricular cardiomyocytes using Ca specific fluorescence dye, Fluo-8/AM. Voltage-gated sodium channels (VGSCs) activation elongates SCO duration and reduces SCO frequency while inhibition of VGSCs decreases SCO frequency without affecting amplitude and duration. Inhibition of voltage-gated potassium channel increases SCO duration. Direct activation of L-type Ca channels (LTCCs) induces SCO bursts while suppressing LTCCs decreases SCO amplitude and slightly increases SCO frequency. Activation of ryanodine receptors (RyRs) increases SCO duration and decreases both SCO amplitude and frequency while inhibiting RyRs decreases SCO frequency without affecting amplitude and duration. The potencies of these ion channel modifiers on SCO responses are generally consistent with their affinities in respective targets demonstrating that modification of distinct targets produces different SCO profiles. We further demonstrate that clinically-used drugs that produce Long-QT syndrome including cisapride, dofetilide, sotalol, and quinidine all induce SCO bursts while verapamil has no effect. Therefore, occurrence of SCO bursts may have a translational value to predict cardiotoxicants causing Long-QT syndrome.