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

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Abstract
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-βII) on L-type calcium channels in isolation from other cardiac isoforms, using a transgenic mouse that conditionally expresses PKC-βII. 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-βII showed a twofold increase in nifedipine-sensitive I Ca. The PKC-βII antagonist LY-379196 returned I Caamplitude to levels found in non-PKC-βII-expressing myocytes. The increase in I Ca was independent of Cav1.2-subunit mRNA levels as determined by quantitative RT-PCR. Thus these data demonstrate that PKC-β is a potent modulator of cardiac L-type calcium channels and that this specific isoform increases I Ca in neonatal ventricular myocytes.