Enhancement of L-type Ca2+ current from neonatal mouse ventricular myocytes by constitutively active PKC-βII

The cardiac L-type calcium current (I-Ca) can be modified by activation of protein kinase C (PKC). However, the effect of PKC activation on I-Ca is still controversial. Some studies have shown a decrease in current, whereas other studies have reported a biphasic effect (an increase followed by a decrease in current or vice versa). A possible explanation for the conflicting results is that several isoforms of PKC with opposing effects on I-Ca were activated simultaneously. Here, we examined the influence of a single PKC isoform (PKC-betaII) on L-type calcium channels in isolation from other cardiac isoforms, using a transgenic mouse that conditionally expresses PKC-betaII. Ventricular cardiac myocytes were isolated from newborn mice and examined for expression of the transgene using single cell RT-PCR after I-Ca recording. Cells expressing PKC-betaII showed a twofold increase in nifedipine-sensitive I-Ca. The PKC-betaII antagonist LY-379196 returned I-Ca amplitude to levels found in non-PKC-betaII-expressing myocytes. The increase in I-Ca was independent of Ca(v)1.2-subunit mRNA levels as determined by quantitative RT-PCR. Thus these data demonstrate that PKC-beta is a potent modulator of cardiac L-type calcium channels and that this specific isoform increases I-Ca in neonatal ventricular myocytes.