Ca2+,Mg2+-ATPase of microsomal membranes from bovine aortic smooth muscle: effects of Sr2+ and Cd2+ on Ca2+ uptake and formation of the phosphorylated intermediate of the Ca2+,Mg2+-ATPase.
The effects of various divalent cations on the Ca2+ uptake by microsomes from bovine aortic smooth muscle were studied. High concentrations (1 mM) of Co2+, Zn2+, Mn2+, Fe2+, and Ni2+ inhibited neither the Ca2+ uptake by the microsomes nor the formation of the phosphorylated intermediate (E approximately P) of the Ca2+,Mg2+-ATPase of the microsomes. The cadmium ion, however, inhibited both the Ca2+ uptake and the E approximately P formation by the microsomes. Dixon plot analysis indicated Cd2+ inhibited (Ki = 135 microM) the Ca2+ dependent E approximately P formation in a non-competitive manner. The inhibitory effect of Cd2+ was lessened by cysteine or dithiothreitol. The strontium ion inhibited the Ca2+ uptake competitively, while the E approximately P formation increased on the addition of Sr2+ at low Ca2+ concentrations. At a low Ca2+ concentration (1 microM), Sr2+ was taken up by the aortic microsomes in the presence of 1 mM ATP. It is thus suggested that Sr2+ replaces Ca2+ at the Ca2+ binding site on the ATPase.
D000818:Animals; D001011:Aorta; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002104:Cadmium / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002413:Cations, Divalent; D002417:Cattle; D008861:Microsomes / Q000201:enzymology; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D010766:Phosphorylation; D013324:Strontium / Q000494:pharmacology*
D002413:Cations, Divalent; D002104:Cadmium; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium; D013324:Strontium