Crosstalk between adenosine A 1 and β 1 ‐adrenergic receptors regulates translocation of PKCε in isolated rat cardiomyocytes

Adenosine A 1 receptor (A 1 R)‐induced translocation of PKCε to transverse (t) tubular membranes in isolated rat cardiomyocytes is associated with a reduction in β 1 ‐adrenergic‐stimulated contractile function. The PKCε‐mediated activation of protein kinase D (PKD) by endothelin‐1 is inhibited by β 1 ‐adrenergic stimulated protein kinase A (PKA) suggesting a similar mechanism of A 1 R signal transduction modulation by adrenergic agonists may exist in the heart. We have investigated the influence of β 1 ‐adrenergic stimulation on PKCε translocation elicited by A 1 R. Immunofluorescence imaging and Western blotting with PKCε and β‐COP antibodies were used to quantify the co‐localization of PKCε and t‐tubular structures in isolated rat cardiomyocytes. The A 1 R agonist CCPA increased the co‐localization of PKCε and t‐tubules as detected by imaging. The β 1 ‐adrenergic receptor agonist isoproterenol (ISO) inhibited this effect of CCPA. Forskolin, a potent activator of PKA, mimicked, and H89, a pharmacological PKA inhibitor, and PKI, a membrane‐permeable PKA peptide PKA inhibitor, attenuated the negative effect of ISO on the A 1 R‐mediated PKCε translocation. Western blotting with isolated intact hearts revealed an increase in PKCε/β‐COP co‐localization induced by A 1 R. This increase was attenuated by the A 1 R antagonist DPCPX and ISO. The ISO‐induced attenuation was reversed by H89. It is concluded that adrenergic stimulation inhibits A 1 R‐induced PKCε translocation to the PKCε anchor site RACK2 constituent of a coatomer containing β‐COP and associated with the t‐tubular structures of the heart. In that this translocation has been previously associated with the antiadrenergic property of A 1 R, it is apparent that the interactive effects of adenosine and β 1 ‐adrenergic agonists on function are complex in the heart. J. Cell. Physiol. 227: 3201–3207, 2012. © 2011 Wiley Periodicals, Inc.