Zinc inhibits cAMP-induced Cl- secretion in intestinal epithelial cells via calcium-sensing receptor (CaSR).

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 I_sc by 60% and its effect was comparable to 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 wildtype 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 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.