Phosphorylation of Ryanodine Receptors in Rat Myocytes during β-Adrenergic Stimulation

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Abstract
We studied β-adrenergic agonist-stimulated phosphorylation of the ryanodine receptor in rat cardiac myocytes. The ryanodine receptor solubilized from myocytes and Immuno-precipitated by a monoclonal antibody against canine cardiac ryanodine receptor was phosphorylated by the catalytic subunit of cAMP-dependent protein kinase (PKA). Incubation of saponin-permeabilized myocytes with [γ-32P] ATP also induced ryanodine receptor phosphorylation, which was enhanced significantly in the presence of isoproterenol. This stimulating action of isoproterenol was suppressed by the β-adrenergic antagonist, propranolol. On the other hand, exogenously added cAMP caused a much larger stimulation of phosphorylation of the ryanodine receptor in permeabilized myocytes. The β-agonist-induced phosphorylation of the ryanodine receptor was also observed in intact myocytes from the newborn rat heart. These results suggest that the ryanodine receptor is phosphorylated by PKA during β-adrenergic stimulation of cardiac myocytes.

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