PROTEIN-KINASE-C ISOFORM EXPRESSION IN NORMAL AND FAILING RABBIT HEARTS

Protein kinase C (PKC) is activated by alpha-adrenergic stimulation. M olecular analysis showed that PKC consists of a family of at least 12 isozymes. Studies of their distribution in the heart showed conflictin g results. The first goal of our study was thus to characterize cardia c PKC in normal rabbits. PKC plays an important role in gene expressio n, cell growth, and differentiation and is involved in the hypertrophy phase of cardiac overload, but since its expression has never been ev aluated in heart failure, the second goal of our study was to evaluate PKC activity and isoform expression in rabbits with heart failure ind uced by a double hemodynamic overload (aortic insufficiency followed b y an aortic stenosis). In the first part of the study, PKC isoform exp ression analyzed in normal rabbits by immunoblotting showed that isofo rms alpha, beta, epsilon, and zeta were expressed along with PKC gamma , which had never been detected in the heart. PKC gamma expression was also identified by polymerase chain reaction, and immunofluorescence techniques showed a localization on intercalated disks associated with the membrane localization observed with the other isoforms. In the se cond part of the study, PKC activity, content, and isoform expression showed a decrease of 37% in the failing group. PKC immunodetection wit h a monoclonal antibody (Mab 1.9) recognizing the catalytic domain of all PKC isoforms revealed a 20% decrease in the failing ventricles com pared with normal left ventricles. Expressed PKC isoforms quantified b y Western blot showed, in the failing heart group compared with the co ntrol group, a decrease of 27%, 32%, 16%, and 9% of PKC alpha, PKC bet a(1), PKC gamma, and PKC epsilon, respectively, whereas PKC zeta was n ot significantly modified. These results show that, in heart failure, PKC activity and expression of Ga2+-dependent PKC isoforms are decreas ed. This may lead to alterations of PKC-induced phosphorylations.