Urotensin II Activates Sarcolemmal Na+/H+ Exchanger in Adult Rat Ventricular Myocytes

Objectives: Our aims in the present study were ( 1) to determine the effects of urotensin II (UT-II) on the sarcolemmal Na+/H+ exchanger (NHE1) activity, and (2) to investigate possible kinase pathways for UT-II-mediated NHE1 stimulation. Methods: In single rat ventricular myocytes (n = 5-10/group) loaded with the pH-sensitive fluoroprobe carboxy-seminaphthorhodafluor-1, acid efflux rates (J(H)) were determined as an index of NHE1 activity by rate of recovery of intracellular pH (pH(i)) from NH4Cl-induced acidosis and the intrinsic buffering power. Phosphorylation of extracellular signal-regulated kinase (ERK), a key kinase of NHE1 activation, was determined by Western blot analysis. Results: J(H) increased by 31%-71% relative to control in the presence of 100 nmol/L UT-II at pH(i) range of 6.6-7.0. Stimulation of NHE1 activity by UT-II was abolished by inhibitors of phospholipase C, protein kinase C, and ERK kinase; 2-nitro-4-carboxyphenil-N,N-diphenilcarbamate at 100 mu mol/L, GF109203X at 300 nmol/L, and PD98059 at 50 mu mol/L, respectively. Moreover, UT-II at 100 nmol/L produced a significant increase in cellular ERK1/2 phosphorylation, which was also inhibited by those inhibitors. Conclusions: Our study was the first to demonstrate that UT-II activates the cardiac sarcolemmal NHE1 and that the phenomenon may involve, at least in part, the phospholipase C-protein kinase C-ERK pathway.