FOCAL LOCALIZATION OF THE NHE-1 ISOFORM OF THE NA+ H+ ANTIPORT - ASSESSMENT OF EFFECTS ON INTRACELLULAR PH/

Na+/H+ exchange (antiport) is a major pathway for the regulation of in tracellular pH. Antiport activity is stimulated when suspended cells a dhere to the substratum. In this report, immunofluorescence was used t o study the subcellular localization of the ubiquitous NHE-1 isoform o f the antiport. NHE-1 was not distributed homogeneously on the surface of the cells. Instead, antiports were found to accumulate along the b order of lamellipodia and near the edge of finer processes. Dual immun ofluorescence experiments demonstrated that vinculin, talin and F-acti n are concentrated at sites of NHE-1 accumulation. A mutated construct of NHE-1 lacking residues 566-635 of the cytosolic domain also accumu lated near marginal lamellae. In contrast, the focal distribution obse rved in adherent cells was not detectable in cells grown in suspension . Fluorescence ratio imaging was used to define the functional consequ ences of focal accumulation of NHE-1. In the steady state, the pH was virtually identical throughout the cytosol. Moreover, no pH gradients were found to develop when cells recovered from an acid load by activa tion of Na+/H+ exchange. This is probably because of the presence of h igh concentrations of mobile buffers in the cytosol. The focal accumul ation of antiporters near the cell margins may be involved in stimulat ion by adherence and/or generation of local osmotic gradients.