Independent and exclusive modulation of cardiac delayed rectifying K+ current by protein kinase C and protein kinase A.

Expression of minK in Xenopus oocytes results in a current similar to the cardiac slow delayed rectifying K+ (IKs) current. Modulation of the IKs current in cardiac myocytes has been studied extensively because of its role in shaping the cardiac action potential. The human and cat minK cDNA have been cloned, but their regulation by protein kinases has not been characterized. We report here on the complex modulation of human and cat IKs currents by protein kinase C (PKC) and protein kinase A (PKA). Activation of PKC by phorbol ester (100 nmol/L phorbol 12,13-didecanoate [PDD]) produces an increase in IKs current that peaks after 20 minutes and then subsequently decreases to approximately 50% of the control level after 1 hour. PKA activation only produces a sustained increase in IKs current. Interestingly, premodulation by PKC prevents IKs current modulation by PKA, and PKC has no effect on IKs current after potentiation by PKA. This shows that the IKs current is modulated by PKC and PKA in a mutually exclusive manner and suggests that multiple interacting phosphorylation sites are involved. Activation of PKC by diacylglycerol analogues only produces a slow decrease in IKs current. The biphasic effects of PKC on IKs current activated by PDD can also be separated by dose and duration. Low doses of PDD (5 nmol/L) or brief applications (5 minutes) of 100 nmol/L PDD only produces IKs current activation. These data suggest that there are at least 2 independent PKC phosphorylation sites in the minK-KvLQT1 channel. Additionally, long-term activation of PKC strongly attenuates the IKs current expression even when the corresponding changes in capacitance are taken into account.