Mechanisms of action of zinc on rat intestinal epithelial electrogenic ion secretion: insights into its antidiarrhoeal actions.

OBJECTIVES: Zinc is a useful addition to oral rehydration therapy for acute diarrhoea. We have assessed the mechanism of its epithelial antisecretory action when intestinal epithelial tight junctions were pharmacologically opened.
METHODS: Rat isolated ileal and colonic mucosae were mounted in Ussing chambers and exposed to ZnSO(4) (Zn(2+) ) in the presence of secretagogues and inhibition of short circuit current (I(sc) ) was measured. KEY
FINDINGS: Pre-incubation with basolateral but not apical Zn(2+) reduced I(sc) stimulated by forskolin, carbachol and A23187. In the presence of the tight junction-opener, cytochalasin D, antisecretory effects of apically-applied Zn(2+) were enabled in colon and ileum. The apparent permeability coefficient (P(app) ) of Zn(2+) was increased 1.4- and 2.4-fold across rat ileum and colon, respectively, by cytochalasin D. Basolateral addition of Zn(2+) also reduced the I(sc) stimulated by nystatin in rat colon, confirming K channel inhibition. In comparison with other inhibitors, Zn(2+) was a relatively weak blocker of basolateral K(ATP) and K (Ca2+) channels. Exposure of ileum and colon to Zn(2+) for 60 min had minimal effects on epithelial histology.
CONCLUSIONS: Antisecretory effects of Zn(2+) on intestinal epithelia arose in part through nonselective blockade of basolateral K channels, which was enabled when tight junctions were open.