Zinc inhibits cAMP-induced Cl^- secretion in intestinal epithelial cells via calcium-sensing receptor

Zinc is a commonly used antidiarrheal supplement; however, its exact mechanism of action is not well understood. Calcium-sensing receptor (CaSR) is a regulator of intestinal ion transport and a therapeutic target for secretory diarrhea. CaSR is activated by various cations and here we investigated the roles of CaSR in the antidiarrheal effects of the divalent metal zinc (Zn²⁺). In human intestinal T84 cells expressing CaSR, zinc (100 µM) inhibited forskolin-induced secretory short-circuit current (I_sc) by 60% and its effect was comparable with CaSR activator cinacalcet. Zinc effect was via inhibition of apical CFTR Cl^- channel and basolateral K⁺ channels. In cell models, zinc was a CaSR agonist and its antisecretory effects were CaSR-dependent. Similarly, 100 µM zinc inhibited forskolin-induced secretory I_sc by 40% in wild-type mouse intestine with no antisecretory effects in intestinal epithelia-specific CaSR knockout mice (Casr^flox/flox;Vil1-cre). Zinc inhibited I_sc induced by clinically-relevant cAMP agonists (cholera toxin and vasoactive intestinal peptide) by 65% in T84 cells. Interestingly, zinc had no effect on cGMP agonists (heat-stable E. coli enterotoxin and linaclotide)-induced secretory I_sc, suggesting that its antisecretory effects are specific to cAMP. The mechanisms of zinc effect in T84 cells involved intracellular Ca²⁺ release via ryanodine receptors and inhibition of cAMP synthesis. Our findings suggest that CaSR activation is a major mechanism for the antidiarrheal effects of zinc, which specifically reduces cAMP levels. In addition to its use in cholera, zinc can be effective in other cAMP-mediated secretory diarrheas.NEW & NOTEWORTHY Zinc is a commonly used antidiarrheal supplement; however, its exact mechanisms of antisecretory effects remain unknown. In this study, we demonstrated that zinc is an agonist of the extracellular calcium-sensing receptor (CaSR) and its antidiarrheal effects are via reduced cAMP synthesis in intestinal epithelial cells. In addition to elucidating the mechanism of action of this antidiarrheal supplement, our data support the use of zinc as a simple and effective treatment option for all cAMP-mediated diarrheas.