Cellular mechanisms underlying the inhibitory effect of flufenamic acid on chloride secretion in human intestinal epithelial cells

Intestinal Cl^- secretion is involved in the pathogenesis of secretory diarrheas including cholera. We recently demonstrated that flufenamic acid (FFA) suppressed Vibrio cholerae El Tor variant-induced intestinal fluid secretion via mechanisms involving AMPK activation and NF-κB-suppression. The present study aimed to investigate the effect of FFA on transepithelial Cl^- secretion in human intestinal epithelial (T84) cells. FFA inhibited cAMP-dependent Cl^- secretion in T84 cell monolayers with IC₅₀ of ∼8 μM. Other fenamate drugs including tolfenamic acid, meclofenamic acid and mefenamic acid exhibited the same effect albeit with lower potency. FFA also inhibited activities of CFTR, a cAMP-activated apical Cl^- channel, and KCNQ1/KCNE3, a cAMP-activated basolateral K⁺ channel. Mechanisms of CFTR inhibition by FFA did not involve activation of its negative regulators. Interestingly, FFA inhibited Ca²⁺-dependent Cl^- secretion with IC₅₀ of ∼10 μM. FFA inhibited activities of Ca²⁺-activated Cl^- channels and K_Ca3.1, a Ca²⁺-activated basolateral K⁺ channels, but had no effect on activities of Na⁺-K⁺-Cl^- cotransporters and Na⁺-K⁺ ATPases. These results indicate that FFA inhibits both cAMP and Ca²⁺-dependent Cl^- secretion by suppressing activities of both apical Cl^- channels and basolateral K⁺ channels. FFA and other fenamate drugs may be useful in the treatment of secretory diarrheas.