Background and purpose: L-type calcium channels (Ca((V))1.2) play an important role in cardiac contraction. Roscovitine, a cyclin-dependent kinase inhibitor and promising anticancer drug, has been shown to affect Ca((V))1.2 by inhibiting current amplitude and slowing activation. This research investigates the mechanism by which roscovitine inhibits Ca((V))1.2 channels.
Experimental approach: Ca((V))1.2 channels were transfected into HEK 293 cells, using the calcium phosphate precipitation method, and currents were measured using the whole-cell patch clamp technique.
Key results: Roscovitine slows activation at all voltages, which precludes one previously proposed mechanism. In addition, roscovitine enhances voltage-dependent, but not calcium-dependent inactivation. This enhancement resulted from both an acceleration of inactivation and a slowing of the recovery from inactivation. Internally applied roscovitine failed to affect Ca((V))1.2 currents, which supports a kinase-independent mechanism and extracellular binding site. Unlike the dihydropyridines, closed state inactivation was not affected by roscovitine. Inactivation was enhanced in a dose-dependent manner with an IC(50)=29.5+/-12 microM, which is close to that for slow activation and inhibition.
Conclusions and implications: We conclude that roscovitine binds to an extracellular site on Ca((V))1.2 channels to inhibit current by both slowing activation and enhancing inactivation. Purine-based drugs could become a new option for treatment of diseases that benefit from L-channel inhibition such as cardiac arrhythmias and hypertension.