beta-Adrenoceptor stimulation potentiates insulin-stimulated PKB phosphorylation in rat cardiomyocytes via cAMP and PKA

Background and purpose: Genetic approaches have documented protein kinase B (PKB) as a pivotal regulator of heart function. Insulin strongly activates PKB, whereas adrenaline is not considered a major physiological regulator of PKB in heart. In skeletal muscles, however, adrenaline potentiates insulin‐stimulated PKB activation without having effect in the absence of insulin. The purpose of the present study was to investigate the interaction between insulin and β‐adrenergic stimulation in regulation of PKB phosphorylation. Experimental approach: Cardiomyocytes were isolated from adult rats by collagenase, and incubated with insulin, isoprenaline, and other compounds. Protein phosphorylation was evaluated by Western blot and phospho‐specific antibodies. Key results: Isoprenaline increased insulin‐stimulated PKB Ser473 and Thr308 phosphorylation more than threefold in cardiomyocytes. Isoprenaline alone did not increase PKB phosphorylation. Isoprenaline also increased insulin‐stimulated GSK‐3β Ser9 phosphorylation approximately twofold, supporting that PKB phosphorylation increased kinase activity. Dobutamine (β1‐agonist) increased insulin‐stimulated PKB phosphorylation as effectively as isoprenaline (more than threefold), whereas salbutamol (β2‐agonist) only potentiated insulin‐stimulated PKB phosphorylation by approximately 80%. Dobutamine, but not salbutamol, increased phospholamban Ser16 phosphorylation and glycogen phosphorylase activation (PKA‐mediated effects). Furthermore, the cAMP analogue that activates PKA (dibutyryl‐cAMP and N6‐benzoyl‐cAMP) increased insulin‐stimulated PKB phosphorylation by more than threefold without effect alone. The Epac‐specific...