The catalytic subunit of cyclic AMP-dependent protein kinase directly inhibits sodium channel activities in guinea-pig ventricular myocytes.

We investigated the effects of the purified catalytic subunit (C subunit) of the cAMP-dependent protein kinase (A-kinase) on the cardiac Na+ channel currents. Single Na+ channel currents in guinea-pig ventricular myocytes were recorded using the patch clamp technique of the inside-out configuration. Application of C subunit decreased the peak average current and slowed the current decay, effects which were caused by decrease in the open probability of Na+ channels and increase in the first latency, whereas the unitary current amplitude and mean open times were not affected. We conclude that the cardiac Na+ channel is directly modulated by phosphorylation process through A-kinase.