Properties of an anion-selective channel from rat colonic enterocyte plasma membranes reconstituted into planar phospholipid bilayers.

Vesicles derived from epithelial cells of the colonic mucosa of the rat were fused to planar phospholipid bilayer membranes, revealing spontaneously switching anion-conducting channels of 50 pS conductance (at -30 mV with 200 mM Cl- each side). The equilibrium selectivity series was I- (1.7)/Br- (1.3)/Cl- (1.0)/F- (0.4)/HCO3- (0.4)/Na (less than 0.11). Only one dominant open-state conductance could be resolved, which responded linearly to Cl- concentrations up to 600 mM. The single-channel current-voltage curve was weakly rectifying with symmetrical solutions. When 50 mV were exceeded at the high-conductance branch of the curve, switching was arrested in the closed state. At more moderate voltages (+/- 40 mV) kinetics were dominated by one open state of about 35-msec lifetime and two closed states of about 2 and 9-msec lifetime. Of these, the more stable closed state occurred less often. At these voltages one additional closed state of significantly longer lifetime (greater than 0.5 sec) was observed.