The calmodulin antagonist W-7 inhibits the epithelial Na+/H+ exchanger via modulating membrane surface potential.

NHE3 is regulated via alterations in membrane surface charge. This is achieved through altered binding of cationic regions in the cytosolic-terminus of the exchanger with the inner leaflet of the plasma membrane. Calmodulin antagonists, including W-7, regulate surface potential and inhibit NHE3 activity. Utilizing fluorescent protein conjugated membrane probes we show that binding of cationic, but not hydrophobic peptides, to the plasma membrane is prevented by W-7. An interaction between cationic regions in the regulatory, cytosolic domain of NHE3 to anionic phospholipids in either reconstituted liposomes or the plasma membrane in cell culture is similarly prevented by W-7, at a concentration that inhibits the exchanger. We propose therefore that W-7 inhibits NHE3 activity, at least in part, by altering the association of cationic segments within the carboxy-terminus of the exchanger with anionic phospholipids in the plasma membrane.