ENDOTHELIN-1-INDUCED PHOSPHOLIPASE-C-BETA AND PHOSPHOLIPASE-D AND PROTEIN-KINASE-C ISOENZYME SIGNALING LEADING TO HYPERTROPHY IN RAT CARDIOMYOCYTES

We have previously demonstrated that stimulation of cultured rat neona tal cardiomyocytes by endothelin-1 (ET-1) induces rapid activation of phospholipase C-beta (PLC-beta), accompanied by transient expression o f proto-oncogenes and subsequent development of hypertrophy and charac teristic phenotypic changes. In the present study we examined the ET-l -induced hypertrophic response in relation to the initial signaling by phospholipase D (PLD) and protein kinase C (PKC). ET-1 (10(-8) M) ind uced hypertrophy after 48 h, as judged by protein/DNA ratio. The forma tion (0.5 h) of C-14-labeled phosphatidylethanol ([C-14]PEth) in the p resence of exogenous ethanol (0.5%) in [C-14]palmitate prelabeled cell s, which reflects the PLD activity, was increased 1.9- and 5.6-fold by ET-1 and phorbolester (PMA, 10(-6) M), respectively. The translocatio n of PKC isoforms from the cytosol to the membrane fraction was examin ed by immunoblot analysis using specific antibodies for PKC-alpha and -epsilon. ET-1 caused a rapid (within 15 s) and sustained disappearanc e of PKC-epsilon but not of PKC-alpha, from the cytosol. The transloca tion of PKC-epsilon to the membrane fraction was just detectable. Howe ver, PMA (10(-7) M) showed a rapid, sustained, and clearly detectable translocation of PKC-alpha and PKC-epsilon. The results indicate that the ET-1-induced development of hypertrophy via activation of distinct PKC isoenzymes may be initiated not only by PLC-beta but also by PLD signaling.