Role for PKC in the adenosine-induced decrease in shortening velocity of rat ventricular myocytes

Abstract

We previously demonstrated that both adenosine receptor activation and direct activation of protein kinase C (PKC) decrease unloaded shortening velocity ( V max) of rat ventricular myocytes. The goal of this study was to further investigate a possible link among adenosine receptors, phosphoinositide-PKC signaling, and V max in rat ventricular myocytes. We determined that the adenosine receptor agonist R-phenylisopropyladenosine ( R-PIA, 100 μM) and the α-adrenergic receptor agonist phenylephrine (Phe, 10 μM) increased turnover of inositol phosphates. PKC translocation from the cytosol to the sarcolemma was used as an indicator of PKC activation. Western blot analysis demonstrated an increased PKC-ɛ translocation after exposure to R-PIA, Phe, and the PKC activators dioctanoylglycerol (50 μM) and phorbol myristate acetate (1 μM). PKC-α, PKC-δ, and PKC-ζ did not translocate to the membrane after R-PIA exposure. Finally, PKC inhibitors blocked R-PIA-induced decreases in V max as well as Ca2+-dependent actomyosin ATPase in rat ventricular myocytes. These results support the conclusions that adenosine receptors activate phosphoinositide-PKC signaling and that adenosine receptor-induced PKC activation mediates a decrease in V max in ventricular myocytes.