Expression of transfected human Na+/H+ exchanger (NHE-1) in the basolateral membrane of opossum kidney cells

Some epithelial cells have Na+/H+ exchanger (NHE) activity in both apical a nd basolateral membranes. Amiloride-sensitive NHE-1 is generally identified in the basolateral membrane. The renal cell line, OK7a, targets amiloride- resistant NHE predominantly to the apical membrane. It is controversial whe ther the transfected NHE-1 is targeted preferentially to the basolateral me mbrane in OK7a cells, when human NHE-1 is chronically expressed under contr ol of constitutively active promoters. We tried to identify the membranes i n which the transfected human NHE-1 could be detected following acute expre ssion in OK7a cells. We have always observed small Na+-dependent pH recover y in the basolateral membrane in OK7a cells. It is, however, controversial whether or not OK7a cells express NHE activity in the basolateral membrane. We also characterized Na+-dependent pH recovery in the basolateral membran e. It was not inhibited by [4,4'-diisothiocyanatostilbene-2,2'-disulfonic a cid] (DIDS), [4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid] ( SITS), or contralateral amiloride. Li+ but not K+, chol(+), or NMC+ could r eplace Na+. These results are consistent with the presence of the NHE in th e basolateral membrane. NHE activities were predominant in the apical membr ane and those in both membranes were resistant to amiloride analogs. After stable transfection with human NHE-1 in a vector utilizing the metallothion ein promoter, overnight induction with Zn2+ increased the NHE activity and its sensitivity to amiloride only in the basolateral membrane in OK7a cells . We conclude that the transfected human NHE-1 is exclusively targeted to t he basolateral membrane of OK7a cells during acute induction. (C) 1999 Wile y-Liss, Inc.