Rutaecarpine Induces Chloride Secretion across Rat Isolated Distal Colon

Abstract

The present study evaluated the effect of rutaecarpine (Rut) on Cl(-) secretion across rat distal colonic mucosa. Basolateral application of Rut elicited an increase in short-circuit current (I(SC)) response in a concentration-dependent manner. Evidence that Rut-stimulated I(SC) was due to Cl(-) secretion is based on 1) inhibition of current by bumetanide; 2) Cl(-) channel blockers diphenylamine-2-carboxylate, 5-nitro-2-(3-phenylpropylamino)-benzoic acid, and glibenclamide; and 3) removal of Cl(-) ions in bath solution. Determination of neurogenic blockers on Rut-induced I(SC) indicated that pretreatment of tissues with tetrodotoxin or indomethacin, but not atropine or hexamethonium, inhibited Rut-induced response. Treatment with Rut led to release and synthesis of prostaglandin E(2) in rat colonic mucosa. Rut-stimulated I(SC) was markedly reduced by pretreatment with MDL-12,330A [cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine] and N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, bisindolylmaleimide, and thapsigargin. Elimination of the extracellular Ca(2+) also did not alter Rut response. Rut treatment resulted in the increase in intracellular cAMP levels and the activation of protein kinase A. Depolarizing the basolateral membrane with high K(+) showed that Rut-stimulated apical Cl(-) current was largely prevented by cystic fibrosis transmembrane conductance regulator (CFTR) inhibitors. Permeabilizing apical membrane with nystatin revealed that Rut-stimulated basolateral K(+) current was specifically inhibited by Ba(2+) ions and chromanol 293B. The evidence derived from present study suggests that Rut-stimulated Cl(-) secretion is mediated by generation of endogenous prostaglandin E(2) and that it also involves the stimulation of cAMP and protein kinase A pathways, which subsequently lead to the activation of apical Cl(-) channels, mostly the CFTR and basolateral cAMP-dependent K(+) channels.