title: Demonstration of a (Ca2+ + Mg2+)-ATPase activity probably related to Ca2+ transport in the microsomal fraction of porcine coronary artery smooth muscle.
abstract: A (Ca2+ + Mg2+)-ATPase activity is demonstrated in the microsomal fraction of porcine coronary artery. The characteristics of the ATPase activity are compared with those of the Ca2+ transport, both measured in similar solutions. It is concluded that the (Ca2+ + Mg2+)-ATPase is related to the Ca2+ transport because: 1. Both transport and ATPase have similar low Km values for Ca2+ as well as comparable Hill coefficients. The Km values are respectively 0.34 +/- 0.03 microM [4] and 1.17 +/- 0.15 microM [6]. The Hill coefficients are n = 1.69 +/- 0.09 [4] and n = 1.23 +/- 0.17 [6]. 2. Ionophores A23187 and X537A stimulate (Ca2+ + Mg2+)-ATPase activity while they inhibit net Ca2+ accumulation by increasing the Ca2+ permeability of the membranes. 3. The V values for Ca2+ accumulation and for (Ca2+ + Mg2+)-ATPase are comparable.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003331:Coronary Vessels / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008861:Microsomes / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D013552:Swine
chemical_list: D004533:Egtazic Acid; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium