Opioid peptide gene expression in the primary hereditary cardiomyopathy of the Syrian hamster. II. Role of intracellular calcium loading.

We have previously shown that prodynorphin gene expression was markedly 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+ concentration was significantly increased in resting and in KCl-depolarized cardiomyopathic myocytes compared with normal cells. In normal and in cardiomyopathic cells, KCl significantly increased prodynorphin mRNA levels and prodynorphin gene transcription. These effects were abolished by the Ca2+ channel blocker verapamil. In control myocytes, the KCl-induced 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, increasing nuclear PKC activity. In resting cardiomyopathic myocytes, the increase in prodynorphin mRNA levels and gene transcription were significantly attenuated by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxy-methylester being completely abolished when the chelating agent was administered in the presence of PKC inhibitors. KCl and the PKC activator 1,2-dioctanoyl-sn-glycerol additively stimulated prodynorphin gene expression both in normal and in cardiomyopathic cells. Therefore, we conclude that PKC activation and intracellular Ca2+ overload may represent the two major signaling mechanisms involved in the induction of the prodynorphin gene in cardiomyopathic cells.