REDOX MODULATION OF L-TYPE CALCIUM CHANNELS IN FERRET VENTRICULAR MYOCYTES - DUAL MECHANISM REGULATION BY NITRIC-OXIDE AND S-NITROSOTHIOLS

The effects of NO-related activity and cellular thiol redox state on b asal L-type calcium current, I-Ca,I-L, in ferret right ventricular myo cytes were studied using the patch clamp technique. SIN-1, which gener ates both NO . and O-2(-), either inhibited or stimulated I-Ca,I-L. In the presence of superoxide dismutase only inhibition was seen. 8-Br-c GMP also inhibited I-Ca,I-L, suggesting that the NO inhibition is cGMP -dependent. On the other hand, S-nitrosothiols (RSNOs), which donate N O+, stimulated I-Ca,I-L. RSNO effects were not dependent upon cell per meability , modulation of SR Ca2+ release, activation of kinases, inhi bition of phosphatases, or alterations in cGMP levels. Similar activat ion of I-Ca,I-L by thiol oxidants, and reversal by thiol reductants, i dentifies an allosteric thiol-containing ''redox switch'' on the L-typ e calcium channel subunit complex by which NO ./O-2(-) and NO+ transfe r can exert effects opposite to those produced by NO .. In sum, our re sults suggest that: (a) both indirect (cGMP-dependent) and direct (S-n itrosylation/oxidation) regulation of ventricular I-Ca,I-L and (b) sar colemma thiol redox state may be an important determinant of I-Ca,I-L activity.