Regulation of gastric acid secretion by the serum and glucocorticoid inducible kinase isoform SGK3

The serum and glucocorticoid inducible kinase isoform SGK3 is ubiquitously expressed and has been shown to participate in the regulation of cell survival and transport. Similar to SGK1 and protein kinase B (PKB/Akt) isoforms, SGK3 may phosphorylate glycogen synthase kinase (GSK) 3 alpha,beta, which has recently been shown to participate in the regulation of basal gastric acid secretion. The present study thus explored the role of SGK3 in the regulation of gastric acid secretion. Experiments were performed in isolated glands from gene-targeted mice lacking functional SGK3 (sgk3 (-/-)) or from their wild-type littermates (sgk3 (+/+)). Utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF) fluorescence, gastric acid secretion was determined from Na+-independent pH recovery (a dagger pH/min) following an ammonium pulse, which reflects H+/K+ adenosine triphosphatase (ATP) ase activity. Cytosolic pH in isolated gastric glands was similar in sgk3 (-/-) and sgk3 (+/+) mice. a dagger pH/min was, however, significantly larger in sgk3 (-/-) than in sgk3 (+/+) mice. In both genotypes, a dagger pH/min was virtually abolished in the presence of the H+/K+ ATPase inhibitor omeprazole (100 mu M) and SCH28080 (500 nM). Increase of extracellular K+ concentrations to 35 mM (replacing Na+/NMDG) or treatment with 5 mu M forskolin increased a dagger pH/min in sgk3 (+/+) mice to a larger extent than in sgk3 (-/-) mice and abrogated the differences between genotypes. The protein kinase A inhibitor H89 (150 nM) decreased a dagger pH/min to similarly low values in both genotypes. SGK3 suppresses gastric acid secretion, an effect presumably mediated by the stimulation of protein kinase A with the subsequent activation of K+ channels.