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Abstract：
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 (ET(B)) and not in cells expressing the endothelin-A (ET(A)) receptor. However, ET-1 causes similar patterns of protein tyrosine phosphorylation, adenylyl cyclase inhibition, and increases in cell [Ca(2+)] in ET(A)- and ET(B)-expressing OKP cells, implying that an additional mechanism is required for NHE3 stimulation by the ET(B) receptor. The present studies used ET(A) and ET(B) 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 ET(A) 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 ET(B) receptor. Within the second intracellular loop, a consensus sequence was identified, KXXXVPKXXXV, that is required for ET-1 stimulation of NHE3 activity. This sequence suggests binding of a homodimeric protein that mediates NHE3 stimulation.
摘要：
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