Role of cholesterol in the structure and function of gastric microsomal vesicles

Abstract

Digitonin was used as a tool to investigate the organization and function of cholesterol in gastric microsomes. Microsomal vesicles were treated with digitonin for different time at 0–4°C under isotonic conditions. The effects of digitonin treatment of the vesicles on removal of cholesterol, ultrastructural changes, (H⁺ + K⁺)‐ATPase activity, and gastric ATPase‐dependent H⁺ uptake ability were investigated. Microsomal cholesterol was extracted in an exponential manner with a t_1/2 of 32 min. There was no release of microsomal phospholipids by digitonin treatment during the same period. Digitonin treatment (30 min) produced visible “holes” in the vesicles; at the same time (H⁺ + K⁺)‐ATPase‐dependent H⁺ uptake was abolished. Under the same conditions the K⁺‐stimulated ATPase activity, however, was moderately (about 35%) reduced, although the response of K⁺ stimulation to valinomycin was obliterated. Longer digitonin treatment resulted in gradual diffusion and eventual disappearance of the “holes” with the generation of distorted cup‐shaped microsomes. The data strongly suggest that membrane lipids are freely mobile and that there is a certain degree of specialization in the organization of gastric microsomal cholesterol for the proper maintenance of the membrane structure and function.