Single anion-selective channels in basolateral membrane of a mammalian tight epithelium

Basolateral membrane chloride permeability of surface cells from rabbit urinary bladder epithelium was studied using the patch-clamp technique. Two types of anion-selective channel were observed. One channel type showed inward rectification and had a conductance of 64 pS at-50 mV when bathed symmetrically by saline solution containing 150 mM chloride; the other resembled high-conductance voltage-dependent anion channels (VDACs). Both channels had the selectivity sequence Cl-approximately equal to Br-approximately equal to I- approximately equal to SCN- approximately equal to NO3- greater than F- greater than acetate greater than gluconate greater than Na+ approximately equal to K+ and were sensitive to the anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Basolateral chloride conductance in urinary bladder is apparently due to the 64 pS anion channel, which is active at physiological potentials. Imperfect selectivity of this channel against cations might also account for the low, but finite, sodium permeability of the basolateral membrane.