OPIOID PEPTIDE GENE-EXPRESSION IN THE PRIMARY HEREDITARY CARDIOMYOPATHY OF THE SYRIAN-HAMSTER .2. ROLE OF INTRACELLULAR CALCIUM LOADING

We have previously shown that prodynorphin gene expression was markedl y increased in adult myocytes of BIO 14.6 cardiomyopathic hamsters and that nuclear protein kinase C (PKC) may be involved in the induction of this opioid gene, Here we report that the cytosolic Ca2+ concentrat ion was significantly increased in resting and in KCl-depolarized card iomyopathic myocytes compared with normal cells, In normal and in card iomyopathic cells, KCl significantly increased prodynorphin mRNA level s and prodynorphin gene transcription, These effects were abolished by the Ca2+ channel blocker verapamil. In control myocytes, the KCl-indu ced increase in prodynorphin mRNA expression was in part attenuated by chelerythrine or calphostin C, two selective PKC inhibitors, In these cells, KCL induced the translocation of PKC-alpha into the nucleus, i ncreasing nuclear PKC activity, In resting cardiomyopathic myocytes, t he increase in prodynorphin mRNA levels and gene transcription were si gnificantly attenuated by the intracellular Ca2+ chelator ,2-bis(2-ami nophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethylester be ing completely abolished when the chelating agent was administered in the presence of PKC inhibitors, KCI and the PKC activator 1,2-dioctano yl-sn-glycerol additively stimulated prodynorphin gene expression both in normal and in cardiomyopathic cells, Therefore, we conclude that P KC activation and intracellular Ca2+ overload may represent the two ma jor signaling mechanisms involved in the induction of the prodynorphin gene in cardiomyopathic cells.