BILE-SALTS STIMULATE MUCIN SECRETION BY CULTURED DOG GALLBLADDER EPITHELIAL-CELLS INDEPENDENT OF THEIR DETERGENT EFFECT

1. Bile salts stimulate mucin secretion by the gallbladder epithelium. We have investigated whether this stimulatory effect is due to a dete rgent effect of bile salts. 2. The bile salts taurocholic acid (TC) an d tauroursodeoxycholic acid (TUDC) and the detergents Triton X-100 (12 .5-400 mu M) and Tween-20 (0.1-3.2 mM) were applied to monolayers of c ultured dog gallbladder epithelial cells. Mucin secretion was studied by measuring the secretion of [H-3]N-acetyl-D-glucosamine-labelled gly coproteins. We also attempted to alter the fluidity of the apical memb rane of the cells through extraction of cholesterol with beta-cyclodex trin (2.5-15 mM). The effect on TUDC-induced mucin secretion was studi ed. Cell viability was assessed by measuring lactate dehydrogenase (LD H) leakage or Cr-51 release. 3. In contrast with the bile salts, the d etergents were not able to cause an increase in mucin secretion withou t causing concomitant cell lysis. Concentrations of detergent that inc reased mucin release (> 100 mu M Triton X-100, > 0.8 mM Tween-20), cau sed increased LDH release. Incubation with beta-cyclodextrin resulted in effective extraction of cholesterol without causing an increase in Cr-51 release. However, no effect of the presumed altered membrane flu idity on TUDC (10 mM)-induced mucin secretion was observed. 4. The sti mulatory effect of bile salts on mucin secretion by gallbladder epithe lial cells is not affected by the fluidity of the apical membrane of t he cells and also cannot be mimicked by other detergents. We conclude that the ability of bile salts to cause mucin secretion by the gallbla dder epithelium is not determined by their detergent properties.