title: Ca2+-transport ATPases of vascular smooth muscle.
abstract: To characterize the Ca2+-transport properties of the plasma membrane and of the endoplasmic reticulum of bovine pulmonary artery, membrane vesicles are subfractionated by a procedure of density-gradient centrifugation that takes advantage of the selective effect of digitonin on the density of plasma-membrane vesicles. The obtained endoplasmic-reticulum fraction contains hardly any plasma-membrane vesicles, whereas the plasma-membrane fraction is still contaminated by a substantial amount of endoplasmic-reticulum vesicles. An adenosine 5'-triphosphate (ATP) energized Ca2+-transport system and a Ca2+-stimulated ATPase activity are present in both subcellular fractions. The Ca2+ transport by the plasma membrane is catalyzed by a (Ca2+,Mg2+)-ATPase of Mr 130,000. It binds calmodulin and it has a low steady-state phosphoprotein intermediate level. The endoplasmic-reticulum vesicles contain a Ca2+-transport ATPase of Mr 100,000 that is characterized by a high steady-state phosphointermediate level. It is antigenically related to the Ca2+-pump protein of cardiac sarcoplasmic reticulum. Phospholamban, the regulatory protein of the Ca2+-transport enzyme of cardiac sarcoplasmic reticulum, is also present in the endoplasmic reticulum of the pulmonary artery. A comparison of these fractions with the previously characterized fractions from porcine gastric smooth muscle reveals important differences in the basal Mg2-ATPase activity, in the ratio of the (Ca2+,Mg2+)-ATPase of the plasmalemma to that of the endoplasmic reticulum, and in the ratio of the (Na+,K+)-ATPase activity to the plasmalemmal (Ca2+,Mg2+)-ATPase activity. These differences can be ascribed in part to the species and in part to the tissue. These data suggest that in the bovine pulmonary artery the Ca2+ extrusion via the ATP-dependent Ca2+ pump may have a less predominant role, and that the Ca2+ uptake by the endoplasmic reticulum, and possibly also the Ca2+ extrusion via the Na+-Ca2+ exchanger could be more important in this tissue than in the porcine stomach.
mesh_terms: D000251:Adenosine Triphosphatases / Q000032:analysis; D000818:Animals; D001692:Biological Transport; D017301:Ca(2+) Mg(2+)-ATPase / Q000032:analysis*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000032:analysis; D000252:Calcium-Transporting ATPases / Q000032:analysis*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008565:Membrane Proteins / Q000032:analysis; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D010750:Phosphoproteins / Q000032:analysis; D000099211:Phospholamban
chemical_list: D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D007811:Lanthanum; D008565:Membrane Proteins; D010750:Phosphoproteins; D000099211:Phospholamban