Prolonged phorbol ester treatment down-regulates protein kinase C isozymes and increases contraction rate in neonatal cardiac myocytes

John A. Johnson, Sudeshna Adak, Daria Mochly-Rosen

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22 Scopus citations


We have determined the effects of chronic exposure to the protein kinase C (PKC) activating drug 4-p phorbol 12-myristate-13-acetate (PMA) on PKC isozymes and the rate of spontaneous contraction in neonatal rat cardiac myocytes in culture. Western blot analyses revealed that a two day exposure to 0.1-1 nM PMA increased the total amount of δPKC, whereas, 100 nM PMA concentrations caused a complete down-regulation of the αPKC and an 80 kDa ζPKC-like protein. In addition, 100 nM PMA treatment for 2 days did not result in complete down-regulation of the β, 6, and εPKC isozymes in Western blot and immunocytochemical studies. We also found a PKC-mediated enhancement of the rate of contraction in these cells following prolonged exposure to PMA (1-100nM). Our studies suggest that this enhancement of contraction rate may be mediated by the β, δ, or εPKC isozymes. A better understanding of the role(s) of PKC isozymes in the modulation of cardiac functions may reveal selective targets for therapies of cardiac disorders.

Original languageEnglish (US)
Pages (from-to)1027-1038
Number of pages12
JournalLife sciences
Issue number11
Publication statusPublished - Aug 4 1995
Externally publishedYes



  • PKC isozymes
  • cardiac myocyte
  • contraction rate
  • phorbol ester

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Pharmacology, Toxicology and Pharmaceutics(all)

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