Transport of sodium into apical membrane vesicles prepared from fetal sheep alveolar type II cells.

A method is described for isolating apical plasma membrane vesicles from fetal alveolar type II cells. The procedure yields purified apical membranes which are enriched 24-fold with the brush-border enzyme marker, alkaline phosphatase. Contamination of this fraction by basolateral membranes and organelles is minimal. Evidence for transport of Na+ into an intravesicular space is demonstrated by: (1) time-dependent uptake of Na+ with release of accumulated Na+ by treatment with detergent; (2) a linear inverse correlation between Na+ uptake and medium osmolarity. In addition, Na+ uptake is shown to be anion dependent (SCN- greater than Cl- greater than gluconate-) and sensitive to amiloride inhibition at a concentration of 1 mM.