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Department of Physiology, University of Tennessee, Memphis, Tennessee 38163
We previously demonstrated that
both adenosine receptor activation and direct activation of protein
kinase C (PKC) decrease unloaded shortening velocity
(Vmax) of rat ventricular myocytes. The goal of
this study was to further investigate a possible link among adenosine
receptors, phosphoinositide-PKC signaling, and Vmax in rat ventricular myocytes. We determined
that the adenosine receptor agonist
R-phenylisopropyladenosine (R-PIA, 100 µM) and the
-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-
translocation after exposure to R-PIA, Phe, and the PKC activators
dioctanoylglycerol (50 µM) and phorbol myristate acetate (1 µM).
PKC-
, PKC-
, and PKC-
did not translocate to the membrane after
R-PIA exposure. Finally, PKC inhibitors blocked
R-PIA-induced decreases in Vmax 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
Vmax in ventricular myocytes.
R-phenylisopropyladenosine; protein kinase C-
; inositol (1,4,5)trisphosphate
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