Bile acid-induced increase of rat colonic apical membrane fluidity and proton permeability.

Rat colonic brush-border membrane vesicle fluidity and passive proton permeability were studied after in vitro exposure to chenodeoxycholate (CDC), taurochenodeoxycholate (TCDC) and taurocholate (TC). The bile acids caused significantly concentration-related increases in colonic membrane fluidity measured by the fluorophore DPH, which is reflecting the fluidity of all membrane layers, but not by 2-AS and 12-AS, which are reflecting the fluidity of the outer membrane layers, indicating that alterations of the membrane fluidity may appear at the inner membrane. Proton permeability (Pnet) of the membranes was increased by the three bile acids CDC, TC and TCDC up to 105%, 126%, 141% and 155% at concentrations of 0.1, 1.0, 1.5 and 3.0 mM, respectively. There were no consistent differences in the potency of the conjugated and unconjugated bile acids. The two variables were significantly positive correlated for the rat colonic brush-border membranes. These data demonstrate direct effects of bile acids on rat colonic brush-border membrane fluidity and proton permeability that are likely to be early events in bile acid-induced mucosal damage.