EXPRESSION OF PROTEIN-KINASE-C ISOFORMS DURING CARDIAC VENTRICULAR DEVELOPMENT

The expression of protein kinase C (PKC) isoforms (PKC-alpha, PKC-beta (1), PKC-delta, PKC-epsilon, and PKC-zeta) was studied by immunoblotti ng in whole ventricles of rat hearts during postnatal development (1-2 6 days) and in the adult. PKC-alpha, PKC-beta, PKC-delta, PKC-epsilon, and PKC-zeta were detected in ventricles of 1-day-old rats, although PKC-alpha and PKC-beta(1) were only barely detectable. All isoforms we re rapidly downregulated during development, with abundances relative to total protein declining in the adult to < 25% of 1-day-old values. PKC-beta(1) was not detectable in adult ventricles. The specific activ ity of PKC was also downregulated. The rat ventricular myocyte becomes amitotic soon after birth but continues to grow, increasing its prote in content 40- to 50-fold between the neonate and the 300-g adult. An important question is thus whether the amount of PKC per myocyte is do wnregulated. With the use of isolated cells, immunoblotting showed tha t the contents per myocyte of PKC-alpha and PKC-epsilon increased simi lar to 10-fold between the neonatal and adult stages. In rat ventricle s, the rank of association with the particulate fraction was PKC-delta > PKC-epsilon > PKC-zeta. Association of these isoforms with the part iculate fraction was less in the adult than in the neonate. In primary cultures of ventricular myocytes prepared from neonatal rat hearts, 1 mu M 12-O-tetradecanoylphorbol-13-acetate (TPA) elicited translocatio n of PKC-alpha, PKC-delta, and PKC-epsilon from the soluble to the par ticulate fraction in < 1 min, after which time no further translocatio n was observed. Prolonged exposure (16 h) of myocytes to 1 mu M TPA ca used essentially complete downregulation of these isoforms, although d ownregulation of PKC-epsilon was slower than for PKC-delta. In contras t, PKC-zeta was neither translocated nor downregulated by 1 mu M TPA. Immunoblotting of human ventricular samples also revealed downregulati on of PKC relative to total protein during fetal/postnatal development .