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The absorption of short chain fatty acids (SCFA) from the rumen requires efficient mechanisms for both apical uptake and basolateral extrusion. Previous studies suggest that the rumen expresses a basolateral chloride conductance that might be permeable to SCFA. In order to characterize this conductance in more detail, isolated cultured ruminal epithelial cells were studied with the patch-clamp technique, revealing a whole cell conductance with p(Cl-) ≈ p(NO3-) > p(HCO3-) > p(acetate-) > p(gluconate-). Currents could be blocked by diisothiocyanato-stilbene-2,2"-disulfonic acid (DIDS; 1 mmol·l-1 > 100 mol·l-1), 5-nitro-2-(3-phenylpropyl-amino)benzoic acid (NPPB; 50 mol·l-1), niflumic acid (100 mol·l-1) and p-chloromercuribenzoate (pCMB; 1 mmol·l-1). Single-channel conductance was 350 ± 7 pS for chloride and 142 ± 7 pS for acetate. Open probability could be fitted with a three-state gating model. We propose a role for this channel in mediating the permeation of chloride, bicarbonate and acetate across the basolateral membrane of the ruminal epithelium.