Roles of mitogen-activated protein kinases and protein kinase C in α1A-adrenoceptor-mediated stimulation of the sarcolemmal Na+-H+ exchanger

Activation of the sarcolemmal Na+-H+ exchanger (NHE) has been implicated as a mechanism of inotropic, arrhythmogenic, antiacidotic, and hypertrophic effects of alpha(1)-adrenoseptor (AR) stimulation Although such regulation of sarcolemmal NHE activity has been shown to be selectively mediated through the alpha(1A)-AR subtype, distal signaling mechanisms remain poorly defined. We investigated the roles of various kinase pathways in alpha(1A)-AR-mediated stimulation of sarcolemmal NHE activity in adult rat ventricular myocytes. as an index of NHE activity, trans-sarcolemmal acid efflux rate (J(H)) was determined through microepifluorescence in single cells, during recovery from intracellular acidosis in bicarbonate-free conditions. Extracellular signal-regulated kinase (ERK), p38-mitogen-activated protein kinase (MAPK), and p90(rsk) activities were indexed on the basis of analysis of their phosphorylation status. In control cells, then was no change in J(H) in response to vehicle. Phenylephrine and A61603, an alpha(1A)-AR subtype-selective agonist, increased J(H) as well as cellular ERK and p90(rsk) activities. Neither agonist affected p38 activity, which was increased with sorbitol. The MAPK kinase inhibitor PD98059 abolished phenylephrine- and A61603-induced increases in J(H) and cellular ERK and p90(rsk) activities. In contrast, the PKC inhibitor GF109203X abolished phenylephrine- and A61603-induced increases in JH but failed to prevent the increases in ERK and p90(rsk) activities. Our findings suggest that alpha(1A)-AR-mediated stimulation of sarcolemmal NHE activity in rat ventricular myocytes requires activation of the ERK (but not the p38) pathway of the MAPK cascade and that the ERK-mediated effect may occur via p90(rsk). Activation of PKC is also required for alpha(1A)-AR-mediated NHE stimulation, but such regulation occurs through an ERK-independent pathway.