Nonmuscle myosin IIA copurifies with chloride channel-enriched membranes from epithelia

Hydrophobic affinity chromatography can be used to isolate, from bovine tracheal epithelial cells, an intracellular membrane vesicle fraction enriched in a single type of chloride channel. The intracellular origin of these vesicles and the function of this chloride channel has not been established. As a first step in this direction, we have purified a 200 kDa protein that copurifies with these membranes. Partial amino acid sequencing and immunoblotting with specific antibodies identify this protein as nonmuscle myosin IIA. Since the vesicle chloride channel is present in plasma membrane fractions as well, we hypothesize that these vesicles represent an intracellular storage or recycling compartment for epithelial chloride channels, which translocate to the plasma membrane during periods of peak demand for epithelial fluid secretion.