PKC-LAMBDA IS THE ATYPICAL PROTEIN-KINASE-C ISOFORM EXPRESSED BY IMMATURE VENTRICLE

We recently identified a developmental decline in protein kinase C (PK C) isoform expression, at the level of the protein, in rat ventricular myocardium. To investigate mechanisms regulating PKC isoform expressi on in cardiac tissue, this study uses Northern blot analysis to compar e the abundance of PKC isoform mRNAs in neonatal and adult rat ventric ular myocardium. PKC-epsilon protein and mRNA were detected in both ne onatal and adult rat ventricular myocardial preparations. In contrast, coordinate postnatal declines in the abundance of PKC-alpha and PKC-d elta proteins and transcripts were identified. An antiserum raised aga inst the COOH-terminal sequence of PKC-zeta detected abundant immunore activity in neonatal, but not adult, ventricular myocytes. However, PK C-zeta transcripts were not detectable in the heart either by Northern blot analysis or a reverse transcriptase-polymerase chain reaction ap proach, indicating that neither the myocytes nor the contaminating cel lular elements in the heart express PKC-zeta. Rather, PKC-lambda, anot her atypical PKC isoform that is structurally highly homologous to PKC -zeta, was detected at the protein and mRNA level in neonatal, but not adult, ventricular myocardium. Taken together, these results establis h that developmental declines in calcium-sensitive, novel, and atypica l PKC isoforms are paralleled by changes in the levels of the mRNAs en coding these proteins, suggesting transcriptional regulation of PKC du ring normal cardiac development. The results of this study further ide ntify PKC-lambda as the atypical PKC isoform expressed by the immature ventricle.