Endothelin-1 chronically inhibits Na/H exchanger-3 in ETB-overexpressing OKP cells

Endothelin-1 (ET-1) acutely increases Na/H antiporter activity in OKPET(B)6 cells, an opossum kidney proximal tubule cell line transfected with ETB re ceptor cDNA. The purpose of the present study was to examine the chronic ef fect of ET-1 on Na/H antiporter activity in OKP cells and to examine whethe r Na/H exchanger (NHE)-3 mRNA and protein abundance are regulated by ET-1, Quiescent OKPET(B)6 cells were treated with 10 nM ET-1 for 3, 6 or 24 h and Na/H antiporter activity was assayed. The Na/H antiporter activity in 3-h ET-1-treated cells was not different from controls. However, Na/H antiporte r activity was significantly decreased by 29% at 6 h and 72% at 24 h. The e ffect of ET-1 on Na/H antiporter activity was blocked by BQ788, an ETB rece ptor antagonist, but not BQ123, an ETA receptor antagonist, The NHE-3 mRNA abundance in ET-1-treated cells was not different from controls at 3 h, How ever, there was a significant decrease in NHE-3 mRNA abundance at 6 and 24 h, There was also a significant decrease in NHE-3 protein abundance at 6 an d 24 h. In summary, ET-1 chronically inhibits NHE-3 in OKPET(B)6 cells. (C) 2000 Academic Press.