Short-chain fatty acids inhibit cAMP-mediated chloride secretion in rat colon

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Abstract
Butyrate stimulates salt absorption in mammalian colon. We examined whether butyrate also affects Cl- secretion. Mucosal segments of distal colon of male Sprague-Dawley rats and T84 cells were studied in Ussing chambers. In control colon, 1 mM dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) increased short-circuit current (Isc) and serosal-to-mucosal Cl- flux (JsmCl) by 3.2 +/- 0.8 and 2.9 +/- 0.8 mueq.cm-2.h-1, respectively. Mucosal or serosal 25 mM butyrate prevented DBcAMP-induced increases in Isc and JsmCl. Four and eight millimolar butyrate caused half-maximal inhibition of the increases in JsmCl and Isc, respectively. Butyrate also inhibited basal JsmCl (by 2.0 +/- 0.4 mueq.cm-2.h-1) but not carbachol-mediated Cl- secretion. The relative inhibitory potency at 25 mM of other short-chain fatty acids (SCFA) paralleled their degree of cellular metabolism: butyrate > acetate = propionate > isobutyrate. At 25 mM, all SCFA reduced mucosal intracellular pH (pHi) transiently by 0.1 pH unit. In intact T84 cells, 50 mM butyrate inhibited the DBcAMP-induced rise in Isc by 55%. In T84 cells with nystatin-permeabilized basolateral membranes, butyrate inhibited the increase in Isc by 82%. We conclude that butyrate inhibits basal and cAMP-mediated Cl- secretion by a mechanism independent of pHi, possibly located at the apical membrane.