Key result
Protein kinase A-catalyzed phosphorylation of rat heart ventricular membranes increased the antiadrenergic effect of adenosine A1 receptor stimulation on adenylyl cyclase activity to approximately 78%.
Cardiac membrane phosphorylation facilitates the cardioprotective antiadrenergic effect of adenosine.
May guide mechanistic studies on cardiac adenosine signaling; leaves open human translation.
Adenosine protects the myocardium of the heart by exerting an antiadrenergic action via the adenosine A1 receptor (A1R). Because beta 1-adrenergic receptor (beta 1R) stimulation elicits myocardial protein phosphorylation, the present study investigated whether protein kinase A (PKA) catalyzed rat heart ventricular membrane phosphorylation affects the beta 1R adrenergic and A1R adenosinergic actions on adenylyl cyclase activity. Membranes were either phosphorylated with PKA in the absence/presence of a protein kinase inhibitor (PKI) or dephosphorylated with alkaline phosphatase (AP) and assayed for adenylyl cyclase activity (AC) in the presence of the beta 1R agonist isoproterenol (ISO) and/or the A1R agonist 2-chloro-N6-cyclopentyladenosine (CCPA). 32P incorporation into the protein substrates of 140-120, 43, and 29 kDa with PKA increased both the ISO-elicited activation of AC by 51-54% and the A1R-mediated reduction of the ISO-induced increase in AC by 29-50%, thereby yielding a total antiadrenergic effect of approximately 78%. These effects of PKA were prevented by PKI. AP reduced the ISO-induced increase in AC and eliminated the antiadrenergic effect of CCPA. Immunoprecipitation of the solubilized membrane adenylyl cyclase with the use of a polyclonal adenylyl cyclase VI antibody indicated that the enzyme is phosphorylated by PKA. These results indicate that the cardioprotective effect of adenosine afforded by its antiadrenergic action is facilitated by cardiac membrane phosphorylation.
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Dobson et al. (2003) studied this question. Protein kinase A (PKA) catalyzed phosphorylation vs. Absence of PKA, presence of PKI, or dephosphorylation with AP was evaluated on Adenylyl cyclase activity (AC). Protein kinase A-catalyzed phosphorylation of rat heart ventricular membranes increased the antiadrenergic effect of adenosine A1 receptor stimulation on adenylyl cyclase activity to approximately 78%.
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