title: Resolution of apical and basal-lateral membrane populations from rat exorbital gland.
abstract: We performed analytical fractionation studies with the goal of isolating basal-lateral and apical membrane vesicles from epithelial cells of rat exorbital lacrimal gland. A density region designated window II contained elements of three physically and biochemically distinct membrane populations. These were resolved by countercurrent distribution in an aqueous polymer two-phase system. One population contained 50% of the NADPH-cytochrome c reductase activity recovered from window II and appeared to be of intracellular origin. A second population contained 70% of the recovered Na-K-ATPase, maximally enriched 42-fold with respect to the initial homogenate. This population was the major locus of alanine transport activity, roughly 85% of which was mediated by systems believed to be characteristic of epithelial cell basal-lateral membranes. It also contained portions of the alkaline phosphatase, galactosyltransferase, acid phosphatase, and NADPH-cytochrome c reductase activities. A third population accounted for 33% of the recovered alkaline phosphatase and was a secondary locus of Na-alanine transport activity, 45% of which could be attributed to systems believed to be characteristic of epithelial cell apical membranes.
mesh_terms: D000409:Alanine / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure*; D002499:Centrifugation, Density Gradient / Q000379:methods; D003377:Countercurrent Distribution; D007765:Lacrimal Apparatus / Q000648:ultrastructure*; D008297:Male; D009251:NADPH-Ferrihemoprotein Reductase / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis
chemical_list: D009251:NADPH-Ferrihemoprotein Reductase; D000469:Alkaline Phosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D000409:Alanine