Functionally distinct pools of actin in secretory cells

Acid secretion by the gastric parietal cell is controlled through movement of vesicles containing the proton pump, the H(+)-K(+)-ATPase (HK). We have used latrunculin B (Lat B), which binds to monomeric actin, to investigate actin turnover in the stimulated parietal cell. In isolated gastric glands, relatively high concentrations of Lat B were required to inhibit acid accumulation (ED(50) approximately 70 microM). Cultured parietal cells stimulated in the presence of low Lat B (0.1--1 microM) have reduced lamellipodia formation and some aberrant punctate phalloidin-stained structures, but translocation of HK and vacuolar swelling appeared unaffected. High Lat B (10--50 microM) resulted in gross changes in actin organization (punctate phalloidin-stained structures throughout the cell and nucleus) and reduced translocation of HK and vacuolar swelling. Resting parietal cells treated with high Lat B showed minor effects on morphology and F-actin staining. If resting cells treated with high Lat B were washed immediately before stimulation, they exhibited a normal stimulated morphology. These data suggest distinct pools of parietal cell actin: a pool highly susceptible to Lat B primarily involved in motile function of cultured cells; and a Lat B-resistant pool, most likely microvillar filaments, that is essential for secretion. Furthermore, the stimulation process appears to accentuate the effects of Lat B, most likely through Lat B binding to monomer actin liberated by the turnover of the motile actin filament pool.