Differential Role of Na+/H+ Exchange Isoforms NHE-1 and NHE-2 in Collecting Duct Cells.

FORD, PAULA; RIVAROLA, VALERIA; CHARA, OSVALDO; PARISI, MARIO; CAPURRO, CLAUDIA

Rio de Janeiro - Brasil

Conferencia; V Iberoamerican Congreso of Biophys; 2003

The Na+/H+ exchanger (NHE) constitutes a gene family containing several isoforms, which display different membrane localizaron and are involved in specialized functions. Although basolateral NHE-1 activity was described in the cortical collecting duct (CCD), the localization and function of other NHE isoforms is not yet clear. This study examines the expression, localization, and regulation of NHE isoforms in a rat cortical collecting duct cell line (RCCD1) which has previously shown to be a good model of CCD cells. Our molecular studies demonstrated the presence of NHE-1 and NHE-2 isoforms, but not NHE-3 and NHE-4, in RCCD1 cells. Cell monolayers, grown on permeable filters, were placed on special holders allowing independent access to apical and basolateral compartments. Intracellular pH (pHi) regulation was spectrofluorometrically studied in basal conditions and after stimulation by NH4Cl acid load or by an hyperosmotic shock. Since arginine-vasopressin (AVP) is involved in Na+ absorption in CCD cells we also tested its putative role in NHEs regulation. In order to difference NHE-1 and NHE-2 roles we have used the well selective HOE-694. The obtained results strongly suggest that NHE-1 and NHE-2 are expressed in the basolateral membrane but they would have differential roles: NHE-1 is responsible of pHi recovery after an acid load while NHE-2 is mainly involved in steady-state pHi and cell volume regulation. Moreover, AVP stimulates NHE-1 isoform, inducing a transient cell alkalinization, which is modulated by Cl/HCO3 exchangers.