Sarcolemmal NHE activity of human ventricular myocytes arises from the NHE1 isoform and is inhibited by HOE-642. Sarcolemmal NHE activity is significantly greater in recipient hearts with chronic end-stage heart failure than it is in unused donor hearts, and this difference is likely to arise from altered posttranslational regulation.

Abstract-Increased sarcolemmal Naϩ /H ϩ exchanger activity has been implicated as a mediator of the cardiac actions of angiotensin II. We studied the receptor subtypes and signaling pathways involved in the regulation of sarcolemmal Na ϩ /H ϩ exchanger activity by angiotensin II in adult rat ventricular myocytes. Cells were loaded with the pH-sensitive fluoroprobe carboxy-seminaphthorhodafluor-1, and acid efflux rates estimated during recovery from intracellular acidosis were used to quantify exchanger activity. Sarcolemmal Na ϩ /H ϩ exchanger activity was not affected by angiotensin II alone but was increased by angiotensin II plus PD123319 (AT 2 antagonist). In contrast, angiotensin II plus losartan (AT 1 antagonist) or CGP42112A (AT 2 agonist) did not affect exchanger activity. The increase in Na ϩ /H ϩ exchanger activity induced by angiotensin II plus PD123319 was blocked by losartan, PD98059 (extracellular signal-regulated kinase inhibitor), GF109203X (protein kinase C inhibitor), and tyrphostin AG1478 (epidermal growth factor receptor kinase inhibitor). Extracellular signal-regulated kinase phosphorylation and activity, measured by immunoblot analysis and an immune-complex kinase assay, respectively, were increased significantly by angiotensin II plus PD123319; these increases were blocked by losartan and PD98059. The increase in extracellular signal-regulated kinase phosphorylation induced by angiotensin II plus PD123319 was blocked also by GF109203X and tyrphostin AG1478. These data show that AT 1 stimulation increases sarcolemmal Na ϩ /H ϩ exchanger activity in adult rat ventricular myocytes and that this response requires extracellular signal-regulated kinase activation through a protein kinase C-and epidermal growth factor receptor-mediated mechanism. The positive effect of AT 1 stimulation on Na ϩ /H ϩ exchanger activity is counteracted by simultaneous AT 2 stimulation through a mechanism that does not involve direct inhibition of the exchanger or attenuation of extracellular signal-regulated kinase activation. (Circ Res. 1999;85:919-930.) Key Words: angiotensin Ⅲ myocyte Ⅲ Na ϩ /H ϩ exchanger Ⅲ signal transduction Ⅲ extracellular signal-regulated kinase T he sarcolemmal Na ϩ /H ϩ exchanger (NHE) of cardiac myocytes consists of the ubiquitous NHE1 isoform of this multigene family 1 and plays an important role in mediating recovery of intracellular pH (pH i ) from acidosis. 2 Although sarcolemmal NHE activity is regulated primarily by pH i and is increased in response to acidosis, it is also subject to modulation by a number of neurohormonal stimuli, 3 such as ␣ 1 -adrenergic agonists 4 endothelin 1 5 and thrombin. 6 These agonists appear to stimulate sarcolemmal NHE activity, through their respective G q protein-coupled receptors, by increasing the exchanger's affinity for intracellular H ϩ , which is the primary mechanism underlying receptor-mediated regulation of NHE1. 7 Several recent studies have suggested that angiotensin II also may stimulate sarcolemmal NHE activity and that a relative intrace...

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