Inhibition of Ca2+-dependent PKC isoforms unmasks ERK-dependent hypertrophic growth evoked by phenylephrine in adult ventricular cardiomyocytes.

OBJECTIVE The duration of extracellular signal-regulated kinase (ERK) activation and the ERK-dependency of hypertrophic growth differ between stimulation of alpha-adrenoceptors or angiotensin II receptors. As both receptor systems activate different protein kinase C (PKC) isoforms, we hypothesized that PKC isoforms contribute to the specific effect of alpha-adrenoceptor stimulation. METHODS Isolated adult ventricular cardiomyocytes from rats were used. Different PKC isoforms were inhibited either pharmacologically by six different PKC inhibitors or specifically downregulated by antisense oligonucleotides. ERK activation was determined by phosphorylation relative to total ERK. The rate of protein synthesis was determined by 14C-phenylalanine incorporation. RESULTS The hypertrophic response of phenylephrine was inhibited in a concentration-dependent fashion by three different inhibitors of Ca2+-independent PKC isoforms (Gö6983, rottlerin, Gö6850), but not by three distinct PKC inhibitors directed preferentially against Ca2+-dependent PKC isoforms (Ro32-0432, HBDDE, Gö6976). Antisense oligonucleotides directed against PKC-alpha, -delta, or -epsilon downregulated their specific isoforms. Their corresponding sense oligonucleotides did not affect PKC isoform expression. The phenylephrine-induced increase in protein synthesis was blocked by antisense oligonucleotides directed against PKC-delta or PKC-epsilon but not PKC-alpha, confirming the pharmacological experiments. Inhibition of Ca2+-dependent PKC isoforms by HBDDE or Gö6976 converted a transient activation of ERK by phenylephrine into a sustained response. Under these conditions, phenylephrine increased protein synthesis in an ERK-dependent way. CONCLUSION Inhibition of Ca2+-dependent PKC isoforms converts the ERK-independent effect of phenylephrine on protein synthesis into an ERK-dependent induction of protein synthesis. We conclude that co-activation of Ca2+-dependent PKC isoforms by phenylephrine contributes to the specific effect on adult ventricular cardiomyocytes from rat.