Hypoxia alters the subcellular distribution of protein kinase C isoforms in neonatal rat ventricular myocytes

Abstract

Cardiac myocytes coexpress multiple protein kinase C (PKC) isoforms which likely play distinct roles in signaling pathways leading to changes in contractility, hypertrophy, and ischemic preconditioning. Although PKC has been reported to be activated during myocardial ischemia, the effect of ischemia/hypoxia on individual PKC isoforms has not been determined. This study examines the effect of hypoxia on the subcellular distribution of individual PKC isoforms in cultured neonatal rat ventricular myocytes. Hypoxia induces the redistribution of PKCα and PKCε from the soluble to the particulate compartment. This effect (which is presumed to represent activation of PKCα and PKCε) is detectable by 1 h, sustained for up to 24 h, and reversible within 1 h of reoxygenation. Inhibition of phospholipase C with tricyclodecan-9-yl-xanthogenate (D609) prevents the hypoxia-induced redistribution of PKCα and PKCε, whereas chelation of intracellular calcium with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) blocks the redistribution of PKCα, but not PKCε; D609 and BAPTA do not influence the partitioning of PKCα and PKCε in normoxic myocytes. Hypoxia, in contrast, decreases the membrane association of PKCδ via a mechanism that is distinct from the hypoxia-induced translocation/activation of PKCα/PKCε, since the response is slower in onset, slowly reversible upon reoxygenation, and not blocked by D609 or BAPTA. The hypoxia-induced shift of PKCδ to the soluble compartment does not prevent subsequent 4-β phorbol 12-myristate- 13-acetate-dependent translocation/activation of PKCδ. Hypoxia does not alter the abundance of any PKC isoform nor does it alter the subcellular distribution of PKCλ. The selective hypoxia-induced activation of PKC isoforms through a pathway involving phospholipase C (PKCα/PKCε) and intracellular calcium (PKCα) may critically influence cardiac myocyte contractility, gene expression, and/or tolerance to ischemia.