NA+ H+ EXCHANGER (NHE) IN THE BASOLATERAL MEMBRANE IS ENCODED BY NHE-1 MESSENGER-RNA IN LLC-PK1 CLONE 4 CELLS/

Several isoforms of Na+/H+ exchanger (NHE-1-5) have been identified. L LC-PK1 clone 4 (CL4) expresses the amiloride-sensitive type of NHE pre dominantly in the basolateral membrane, which is believed to be NHE-1. It is not clear whether CL4 expresses NHE in the apical membrane and which side of NHE is encoded by the NHE-1 mRNA. Using acidified CL4 ce lls on the filler membrane, we examined Na+-dependent pH recovery of t he apical and basolateral membranes separately. Na+ applied to the api cal membrane recovered cell pH. Na+-dependent pH recovery in the apica l membrane was not inhibited by SITS, DIDS, or contralateral amiloride . Li+ but not K+, chol(+), or NMG(+) could replace Na+. These data are consistent with the presence of NHE in the apical membrane. Transfect ion with an antisense oligonucleotide corresponding to the 5' terminal site of NHE-1 cDNA of CL4 decreased NHE activity in the basolateral m embrane but not in the apical membrane. We conclude that CL4 expresses NHE activities in both apical and basolateral membranes and that NHE- 1 mRNA encodes NHE only in the basolateral membrane. (C) 1997 Wiley-Li ss, Inc.