The effect of short-chain fatty acids on Cl? and K+ conductance in rat colonic crypts

Publisher Website
Google Scholar
Abstract
The effect of butyrate on membrane potential and membrane currents of colonic enterocytes was studied with the whole-cell patch-clamp method. Superfusion of crypts from the rat distal colon with butyrate-containing solutions induced a membrane depolarization of 16.5±2.3 mV. This response was only observed in the upper third of the crypt. The depolarization was dependent on the presence of Cl− and was accompanied by an increase in membrane inward current, indicating that it is caused by an increase in Cl− conductance. Membrane outward current, however, behaved inconsistently. Whereas in most cells an increase was observed, about 25% of the cells responded with a decrease. This unexpected inhibition of the outward current probably represents a decrease of K+ conductance caused by the cellular acidification in the presence of butyrate. Ma-noeuvres carried out to acidify the cell interior, like perfusion with acid buffer solutions or inhibition of the Na+/H+ exchanger by amiloride, mimicked this inhibition of the K+ conductance. Orientating cell-attached patch-clamp recordings performed in parallel revealed an activation of previously silent basolateral Cl− channels by butyrate. They had a linear current/voltage relationship and a single-channel conductance of 20–30 pS. The butyrate-induced depolarization was not dependent on intracellular adenosine 5′-triphosphate (ATP) and was also observed when the buffer capacity of the pipette for Ca2+ was increased. It was also not inhibited by guanosine-5′-O(2-thiodiphosphate) (GDP[βS]). In the presence of the lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), the butyrate response was inhibited and even reversed to a slight hyperpolarization indicating that the butyrate-induced Cl− channels, but not the K+ channels, are stimulated by a leukotriene. The effect of butyrate could be mimicked by administration of leukotriene D4 (LTD41, 5×10−7 mol · l−1). The eicosanoid induced a depolarization, which was completely dependent on the presence of Cl−. Consequently, LTD4 is a likely candidate for the lipoxygenase metabolite, which activates basolateral Cl− channels. This activation seems not to be mediated by a protein phosphorylation or a G-protein.