Cloning and characterization of Na+/H+ Exchanger isoforms NHE2 and NHE3 from the gill of Pacific dogfish Squalus suckleyi

Na+/H+ Exchanger (NHE) proteins mediate cellular and systemic homeostasis of sodium and acid and may be the major sodium uptake method for fishes. We cloned and sequenced NHE2 and NHE3 from the gill of the North Pacific Spiny Dogfish shark Squalus suckleyi and expressed them in functional form in NHE-deficient (AP-1) cell lines. Estimated IC50 for inhibition of NHE activity by amiloride and EIPA were 55 μmol l− 1 and 4.8 μmol l− 1, respectively, for NHE2 and 9 μmol l− 1 and 24 μmol l− 1, respectively, for NHE3. Phenamil at 100 μmol l− 1 caused less than 16% inhibition of activity for each isoform. Although the IC50 are similar for the two isoforms, dfNHE2 is less sensitive than human NHE2 to inhibition by amiloride and EIPA, while dfNHE3 is more sensitive than human NHE3. These IC50 estimates should be considered when selecting inhibitor doses for fishes and for reinterpretation of previous studies that use these pharmacological agents.