STATE OF ACTIN IN GASTRIC PARIETAL-CELLS

Remodeling of the apical membrane-cytoskeleton has been suggested to o ccur when gastric parietal cells are stimulated to secrete HCl. The pr esent experiments assayed the relative amounts of F-actin and G-actin in gastric glands and parietal cells, as well as the changes in the st ate of actin on stimulation. Glands and cells were treated with a Noni det P-40 extraction buffer for separation into detergent-soluble (supe rnatant) and detergent-insoluble (pellet) pools. Two actin assays were used to quantitate actin: the deoxyribonuclease I binding assay to me asure G-actin and F-actin content in the two pools and a simple Wester n blot assay to quantitate the relative amounts of actin in the pools. Functional secretory responsiveness was assayed by aminopyrine accumu lation. About 5% of the total parietal cell protein is actin, with abo ut 90% of the actin present as F-actin. Stimulation of acid secretion resulted in no measurable change in the relative amounts of G-actin an d cytoskeletal F-actin. Treatment of gastric glands with cytochalasin D inhibited acid secretion and resulted in a decrease in F-actin and a n increase in G-actin. No inhibition of parietal cell secretion was ob served when phalloidin was used to stabilize actin filaments. These da ta are consistent with the hypothesis that microfilamentous actin is e ssential for membrane recruitment underlying parietal cell secretion. Although the experiments do not eliminate the importance of rapid exch ange between G-and F-actin for the secretory process, the parietal cel l maintains actin in a highly polymerized state, and no measurable cha nges in the steady-state ratio of G-actin to F-actin are associated wi th stimulation to secrete acid.