Membrane lipid composition and susceptibility to bile salt damage.

Erythrocyte membranes with low sphingomyelin : choline-containing phospholipid ratios haemolyse at low concentrations of the bile salt, glycocholate. Erythrocytes with higher sphingomyelin : choline-containing phospholipid ratios require progressively greater concentrations of the bile salt for lysis. Sublytic concentrations of glycocholate remove phospholipid and acetylcholinesterase from the membranes. Membranes with low sphingomyelin : choline-containing phospholipid ratios lose both particulate (microvesicles of distinct composition) and 'solubilized' material, the particulate form predominating. The proportion of particulate material falls with increase of the membrane sphingomyelin : choline-containing phospholipid ratio and those membranes of highest sphingomyelin : choline-containing phospholipid ratio lose material predominantly in 'solubilized' form. Sheep erythrocytes treated to increase their content of phosphatidylcholine (and thereby reduce their membrane sphingomyelin : choline-containing phospholipid ratio) become more susceptible to lysis by glycocholate. These observations indicate a correlation between membrane lipid composition and the perturbation of membranes with bile salt; they also point to possible features of membranes capable of surviving exposure to the high bile salt concentrations of the biliary tract.