title: Ca2+-dependent ATPase activity of alveolar macrophage plasma membrane.
abstract: A plasma membrane fraction was isolated from lysates of Bacillus Calmette-Guérin-induced alveolar macrophages of rabbit. On the basis of morphological and biochemical criteria this fraction appeared to be minimally contaminated by other subcellular organelles. Concentrations of Ca2+, but not of Mg2+, from 6.10(-8) to 1.10(-5) M markedly stimulated the basal ATPase (EC 3.6.1.3) activity of the plasma membrane, with an apparent Km (Ca2+) of 1.10(-6) M. The specific activity of the Ca2+-ATPase assayed at pCa = 5.5 was enriched about 8-fold in the plasma membrane fraction over the macrophage lysate. In contrast, the specific activity of the K+, EDTA-activated ATPase, associated to macrophage myosin, increased only 1.3-fold. Oligomycin and -SH group reagents exerted no influence on the Ca2+-ATPase activity, which was on the contrary inhibited by detergents such as Triton X-100 and deoxycholate. The activity of the Ca2+-ATPase was maximal at pH 7, and was decreased by 50 mM Na+ and 5 mM K+. On the contrary, the activity of Mg2+-ATPase, also present in the plasma membrane fraction, had a peak at about pH 7.8, and was stimulated by Na+ plus K+. On account of its properties, it is suggested that the Ca2+-ATPase is a component of the plasma membrane of the alveolar macrophage, and that its function may be that of participating in the maintenance of low free Ca2+ concentrations in the macrophage cytosol.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001500:BCG Vaccine / Q000008:administration & dosage; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000378:metabolism; D066298:In Vitro Techniques; D008264:Macrophages / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D011092:Polyethylene Glycols / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000378:metabolism*; D011817:Rabbits
chemical_list: D001500:BCG Vaccine; D011092:Polyethylene Glycols; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium