Impaired intestinal NHE3 activity in the PDK1 hypomorphic mouse

In vitro experiments have demonstrated the stimulating effect of serum- and glucocorticoid-inducible kinase (SGK)1 on the activity of the Na+/H+ exchanger (NHE3). SGK1 requires activation by phosphoinositide-dependent kinase (PDK)1, which may thus similarly play a role in the regulation of NHE3-dependent epithelial electrolyte transport. The present study was performed to explore the role of PDK1 in the regulation of NHE3 activity. Because mice completely lacking functional PDK1 are not viable, hypomorphic mice expressing ∼20% of PDK1 (pdk1hm) were compared with their wild-type littermates (pdk1wt). NHE3 activity in the intestine and PDK1-overexpressing HEK-293 cells was estimated by utilizing 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein fluorescence for the determination of intracellular pH. NHE activity was reflected by the Na+-dependent pH recovery from an ammonium prepulse (ΔpHNHE). The pH changes after an ammonium pulse allowed the calculation of cellular buffer capacity, which was not significa...