The alpha 1A-adrenergic receptor subtype mediates biochemical, molecular, and morphologic features of cultured myocardial cell hypertrophy

Abstract

alpha 1-Adrenergic agonists induce a hypertrophic phenotype in cultured neonatal rat ventricular myocytes. Quantifiable markers of this phenotype include stimulation of phosphoinositide hydrolysis, transcriptional induction of atrial natriuretic factor (ANF) gene expression, and an increase in myocardial cell size. The aim of the present work was to determine which alpha 1-adrenergic receptor subtype mediates the acquisition of these parameters of myocardial cell hypertrophy. Phosphoinositide hydrolysis is inhibited by low concentrations of 5-methylurapidil (log Ki = -8.7) and (+)-niguldipine (log Ki = -10.6). The alpha-adrenergic receptor-induced increase in transcriptional activation of an ANF luciferase reporter gene is inhibited over the same range of concentrations of 5-methylurapidil (log Ki = -8.2) and (+)-niguldipine (log Ki = -11.2) that inhibit phosphoinositide hydrolysis. In addition, the increase in cell size that accompanies alpha-adrenergic receptor stimulation of cultured ventricular myocytes is blocked by similar concentrations of 5-methylurapidil (log Ki = -8.0) and (+)-niguldipine (log Ki = -10.6). In contrast, treatment with the alpha 1B selective antagonist chlorethylclonidine at a concentration of 10 microM had no effect on the adrenergically mediated induction of ANF luciferase reporter gene expression or the adrenergically induced increase in myocardial cell size. These findings demonstrate that pharmacologically identifiable alpha 1A-adrenergic receptors mediate not only the early effects of alpha 1-adrenergic stimulation such as phosphoinositide hydrolysis, but that they activate the signaling pathways that control transcriptional induction of the ANF luciferase reporter gene and an increase in myocardial cell size. Studies using alpha 1-adrenergic receptor cDNAs to delineate and alter the direct interaction of this receptor subtype with proximal signaling molecules, e.g. GTP binding proteins, should provide a powerful means of assessing their role in the induction of the molecular and morphologic parameters of myocardial cell hypertrophy.