Effect and signaling pathway of epinephrine on the Na⁺-K⁺ ATPase in Caco-2 cells -

Abstract

Epinephrine, a key stress hormone, has been shown to affect the physiological homeostasis of several biological processes in various body systems. In the gastrointestinal tract, stress has been associated with alterations in colonic functions leading to changes in water movements manifested as diarrhea or constipation. Colonic water movement is driven by the Na⁺-gradient created by the Na⁺-K⁺-ATPase. Whether epinephrine acts via an effect on the Na⁺-K⁺-ATPase hasn’t been studied before. In this work, we aim to investigate the effect of epinephrine on the Na⁺-K⁺-ATPase and to elucidate the signaling pathway involved by using CaCo-2 cells as a model. The activity of the Na⁺-K⁺-ATPase was assayed by measuring ATP hydrolysis in presence and absence of ouabain, a specific inhibitor of the enzyme. Epinephrine, added for 20 minutes, decreased the activity of the Na⁺-K⁺-ATPase by 50percent. This effect was found to be mediated by α2 adrenergic receptors as it was fully abolished in the presence of Yohimbine an α2-blocker, but persisted in presence of other adrenergic antagonists. Furthermore, treatment with Rp-cAMP, a PKA inhibitor, mimicked epinephrine’s negative effect and didn’t result in any additional inhibition when both were added simultaneously. Treatment with indomethacin, PTIO, calphostin C, and PD98059, the respective inhibitors of PGE2, NO, PKC, and ERK completely abrogated the effect of epinephrine. In addition, an inhibitory effect, similar to that of epinephrine’s, was observed upon incubation with PGE2, SNAP-1(NO generator), or PMA (PKC activator). PGE-2 was shown to act by binding to its EP1-receptors since its effect disappeared in presence of SC19220, an EP1-receptor antagonist. PGE2 failed to decrease the activity of the Na⁺-K⁺-ATPase in presence of PTIO and Calphostin C .Similarly, PMA’s negative effect was not observed when added with PTIO, but persisted in the presence of indomethacin.