Roscovitine as the Archetypal Member of a Novel Class of Antiarrhythmics Targeting Late ICa,L

L-type calcium current (ICa,L) plays a central role in counterbalancing potassium current during the plateau phase of cardiac action potential (AP). When repolarization reserve is reduced, the aberrant reactivation of ICa,L during repolarization can cause transient depolarization events called Early Afterdepolarizations (EADs), a recognized trigger of cardiac arrhythmias. Recently we demonstrated that EADs are highly sensitive to the steady-state voltage-dependent properties of ICa,L. Using the dynamic clamp technique in isolated rabbit ventricular myocytes under EAD-favoring condition (i.e. oxidative stress or hypokalemia), we found that selectively inhibiting the non-inactivating component (late) of ICa,L potently suppressed EAD-occurrence. Roscovitine, a purine analog, has been shown to reduce the late ICa,L component while leaving peak unperturbed. Here we tested the ability of this drug to suppress EADs in isolated rabbit ventricular myocytes induced by exposure to H2O2 (600µM). This oxidative stress caused EADs in 81% [95% CI: 66-95%] of the APs, prolonging AP duration (APD90) from 276 ms [97-433 ms] to 840ms [285-1967ms] (n=4). Addition of roscovitine (20µM) completely abolished EADs and reduced the APD90 to 189 ms [155-222 ms]. Moreover, roscovitine did not significantly perturb the Ca transient, implying maintenance of normal excitation-contraction coupling. We next exposed isolated aged rat hearts to 0.1 mM H2O2 to induce EADs and spontaneous ventricular tachycardia/fibrillation (VT/VF). In all tested hearts (n=4), roscovitine terminated VT/VF and led to resumption of sinus rhythm within 10 min. Our study offers additional proof of concept supporting a pharmacological strategy to target late ICa,L to prevent EAD-mediated arrhythmias, with roscovitine as an archetypal drug to guide the development of this new class of antiarrhythmics.