ETB receptor activation causes exocytic insertion of NHE3 in OKP cells

Endothelin-1 (ET-1) activates sodium/hydrogen exchanger 3 (NHE3) in opossum kidney clone P (OKP) cells expressing ETB receptors. ET-1 (10(-8) M) cause d a two- to threefold increase in apical membrane NHE3 (assessed by surface biotinylation), in the absence of a change in total cellular NHE3. A maxim al effect was achieved within 15 min. The increase in apical NHE3 was not b locked by cytochalasin D but was blocked by latrunculin B, which also preve nted the ET-1-induced increase in NHE3 activity. Endocytic internalization of NHE3, measured as protection of biotinylated NHE3 from the membrane-impe rmeant, sulfhydryl-reducing agent MesNa was minimal within 35 min and was n ot regulated by ET-1. Exocytic insertion of NHE3, measured as the appearanc e of biotinylated NHE3 after the blockade of reactive sites with sulfo-NHS- acetate, was increased in response to ET-1. These studies demonstrate that ET-1 induces net trafficking of NHE3 to the apical membrane that is mediate d by enhanced exocytic insertion and is required for increased NHE3 activit y.