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Isolated Cells of the Sheep Rumen and Omasum Express Maxi‐anion Channels Permeable to Acetate, Propionate and Butyrate

Large quantities of short chain fatty acids (SCFA) are absorbed by the gut, representing the major source of energy in the ruminant. Both salivary buffering of SCFA in the forestomachs and intraepithelial mechanisms are necessary to prevent clinical complications. A recent study suggests that basolateral efflux of acetate from the rumen of sheep may occur through an anion channel with p(Cl−) ~350 pS and p(acetate−) ~140 pS. Using the patch clamp technique, we investigated the permeability of this channel for other SCFA and demonstrate its expression by cells isolated from the omasum. Whole cell currents were sensitive to DIDS and p‐chloromercuribenzoate with p(Cl−) > p(acetate−) > p(propionate−) > p(butyrate−) > p(gluconate−). Inside‐out data in symmetrical NMDG‐propionate solution showed a conductance of 114 ± 10 pS for propionate−. The size of channel events at positive pipette potential changed with the dominant anion in the bath, confirming the permeability sequence obtained. Data from asymmetric solutions could be fitted with a model assuming independence, with marginal negative interaction. We propose that protons taken up with SCFA are extruded apically via Na+/H+ exchange. While butyrate is mostly metabolized, the anions of acetate‐ and propionate‐ leave basolaterally via the channel described, driven by the potential generated by the Na+‐K+‐ATPase. German Sci. Found. STU 258/4‐1; Schaumann Stiftung