ACUTE ALPHA-1-ADRENERGIC STIMULATION OF CARDIAC PROTEIN-SYNTHESIS MAY INVOLVE INCREASED INTRACELLULAR PH AND PROTEIN-KINASE ACTIVITY

In the presence of 5 mu-M-DL-propranolol and in HCO3-containing buffers, 1 mu-M-adrenaline acutely stimulated protein synthesis by about 25% in the anterogradely perfused rat heart. This stimulation was opposed by low (1-10 nM) concentrations of prazosin, but not by similar concentrations of yohimbine, suggesting involvement of the alpha-1-adrenoceptor. Under the same conditions, adrenaline raised intracellular pH (pH(i)) by about 0.1 unit. The increase in pH(i) induced by adrenaline was prevented by 5 nM-prazosin, but not by 5 nM-yohimbine, again suggesting involvement of the alpha-1-adrenoceptor. Since an increase in pH(i)) stimulates protein synthesis in the heart [Sugden & Fuller (1991) Biochem. J. 273, 339-346], the increase in pH(i) induced by adrenaline may be involved in its stimulation of protein synthesis. Adrenaline also increased phosphocreatine concentrations. As discussed, the increase in pH(i) induced by adrenaline may be responsible for this effect. Using second-order polynomial regression analysis, we showed that rates of protein synthesis were significantly correlated (P < 0.0001) with phosphocreatine concentrations. We discuss two possible reasons for this correlation: (i) increases in pH(i) stimulates protein synthesis and separately raise phosphocreatine concentrations, or (ii) the increase in protein synthesis rates is a consequence of the raised phosphocreatine concentrations induced by the increase in pH(i). Rates of protein synthesis were not significantly correlated with ATP/ADP concentration ratios, nor with any of the following: ATP, ADP, AMP or total adenine nucleotide concentrations. In freshly isolated adult rat cardiomyocytes, the protein kinase inhibitor staurosporine (1 mu-M) prevented stimulation of protein synthesis by 0.3 mu-M-adrenaline (and by 1 mu-M-phorbol 12-myristate 13-acetate or 1 m-unit of insulin/ml). The results are discussed within a mechanistic framework initiated by stimulation of the hydrolysis of membrane phospholipids by alpha-1-adrenergic agonists.