Gastrin Stimulates Na, K‐ATPase Phosphorylation and Endocytosis via PI3 kinase‐mTOR‐S6 Kinase and PKC Pathways in Immortalized Renal Proximal Tubule Cells

Several enterokines have been postulated to mediate postprandrial natriuresis. However, the renal uptake of gastrin is several‐fold higher than that observed for cholecystokinin, bombesin, neurotensin, or somatostatin. We hypothesized that gastrin is the major enterokine mediating postprandial natriuresis. The aim of this study was to determine the molecular and cellular mechanisms involved in the short‐term regulation of Na, K‐ATPase by gastrin. We found that gastrin (100 nM/3hr) treatment of renal proximal tubule cells from a normotensive male caused activation of PI3 kinase‐mTOR‐S6 pathway as reflected by increased phosphorylation of S6 (80%, n=3). The phosphorylation of S6 was biphasic, increasing from 10 to 300nM, but decreasing at 1 μM concentrations. The phosphorylation of serine 16 of Na, K‐ATPase showed a similar pattern (> 4 fold‐ increase at 100 nM, n=3). Blocking PI3 kinase with wortmannin (1 μM) or PKC with chelerytherine (10 μM) abolished the gastrin‐mediated S6 and Na,K‐ATPase phosphorylation. Gastrin (100–300 nM/3 hr) also increased the endocytosis of serine 16 phosho‐Na, K‐ATPase. These findings suggest that one of the mechanisms by which gastrin induces a natriuresis is by decreasing the plasma membrane level of Na, K‐ATPase via endocytosis, and such a process is mediated by both PI3 kinase and PKC pathways.