DIFFERENTIAL ACTIVATION OF PROTEIN-KINASE-C ISOFORMS BY ENDOTHELIN-1 AND PHENYLEPHRINE AND SUBSEQUENT STIMULATION OF P42 AND P44 MITOGEN-ACTIVATED PROTEIN-KINASES IN VENTRICULAR MYOCYTES CULTURED FROM NEONATALRAT HEARTS

The translocation of protein kinase C (PKC) isoforms PKC-alpha, PKC-de lta, PKC-epsilon, and PKC-zeta from soluble to particulate fractions w as studied in ventricular cardiomyocytes cultured from neonatal rats, Endothelin-1 (ET-1) caused a rapid, ET(A) receptor-mediated translocat ion of PKC-delta and PKC-epsilon (complete in 0.5-1 min). By 3-5 min, both isoforms were returning to the soluble fraction, but a greater pr oportion of PKC-epsilon remained associated with the particulate fract ion, The EC(50) of translocation for PKC-delta was 11-15 nM ET-1 where as that for PKC-epsilon was 1.4-1.7 nM. Phenylephrine caused a rapid t ranslocation of PKC-epsilon (EC(50) = 0.9 mu M), but the proportion lo st from the soluble fraction was less than with ET-1. Translocation of PKC-delta was barely detectable with phenylephrine. Neither agonist c aused any consistent translocation of PKC-alpha or PKC-zeta. Activatio n of p42 and p44 mitogen-activated protein kinase (MAPK) by ET-1 or ph enylephrine followed more slowly (complete in 3-5 min), Phosphorylatio n of p42-MAPK occurred simultaneously with its activation, The proport ion of the total p42-MAPK pool phosphorylated in response to ET-1 (50% ) was greater than with phenylephrine (20%), In addition to activation of MAPK, an unidentified p85 protein kinase was activated by ET-1 in the soluble fraction whereas an unidentified p58 protein kinase was ac tivated in the particulate fraction.