A consensus sequence in the endothelin-B receptor second intracellular loop is required for NHE3 activation by endothelin-1

Endothelin-1 (ET-1) increases the activity of Na+/H+ exchanger 3 (NHE3), the major proximal tubule apical membrane Na+/H+ antiporter. This effect is seen in opossum kidney (OKP) cells expressing the endothelin-B (ETB) and not in cells expressing the endothelin-A (ETA) receptor. However, ET-1 causes similar patterns of protein tyrosine phosphorylation, adenylyl cyclase inhibition, and increases in cell [Ca2+] in ETA- and ETB-expressing OKP cells, implying that an additional mechanism is required for NHE3 stimulation by the ETB receptor. The present studies used ETA and ETB receptor chimeras and site-directed mutagenesis to identify the ET receptor domains that mediate ET-1 regulation of NHE3 activity. We found that binding of ET-1 to the ETA receptor inhibits NHE3 activity, an effect for which the COOH-terminal tail is necessary and sufficient. ET-1 stimulation of NHE3 activity requires the COOH-terminal tail and the second intracellular loop of the ETB receptor. Within the second intracellular loop, a con...