Effects of short-chain fatty acids on cell volume regulation and chloride transport in the rat distal colon

Abstract

Superfusion of isolated crypts from rat colon with sodium butyrate-containing solutions induced an amiloride-sensitive swelling of the cells at the upper one-third of the crypt. In HCO3(-)-containing buffer, swelling was followed by regulatory volume decrease, which was inhibited by K+ and C- channel blockers and inhibitors of leukotriene synthesis. Whole-cell patch-clamp recordings revealed that butyrate induced a membrane depolarization, which was dependent on Cl- and was accompanied by an increase in membrane inward current, indicating an increase in Cl- conductance. Membrane outward (K+) current, however, behaved inconsistently, suggesting an activation of swelling-induced K+ currents, but an inhibition of pH-sensitive K+ currents due to the cellular acidification. Cell-attached patch-clamp recordings showed an activation of basolateral Cl- channels by butyrate. The lipoxygenase inhibitor, NDGA (nordihydroguaiaretic acid), inhibited the butyrate response and even reversed it into a slight hyperpolarization indicating that the butyrate-induced Cl- channels, but not the K+ channels, are stimulated by a leukotriene. Short-chain fatty acids concentration-dependently decreased short-circuit current (Isc). The decrease in Isc was diminished by a Cl- channel blocker, NPPB (5-nitro-2-[3-phenylpropylamino]-benzoate), and a lipoxygenase inhibitor, NDGA. Butyrate stimulated the mucosa to serosa fluxes (Jms) of Na+ and Cl-. The effect on J(ms)Cl was blocked by NPPB or NDGA. The stimulation of J(ms)Cl correlated with the degree of metabolism of the short-chain fatty acid. Consequently, two factors seem to be responsible for the stimulation of Cl- absorption by short-chain fatty acids: (a) the intracellular production of HCO3- during the oxidation of short-chain fatty acids as substrate for the apical Cl-/HCO3- exchanger, and (b) the activation of volume-sensitive basolateral Cl- channels.