Cardiac sarcolemmal and sarcoplasmic reticulum membrane vesicles exhibit distinctive (Ca-Mg)-ATPase substrate specificities.
The nucleoside 5'-triphosphate (NTP) substrate specificities for Ca-stimulated ATPase and ATP-dependent Ca2+ uptake activities have been examined in cardiac sarcolemma (SL) and sarcoplasmic (SR) membrane vesicles. The results indicate that SL membrane vesicles exhibit a much narrower range of NTP substrate specificities than SR membranes. In SR membrane vesicles, the Ca-stimulated Mg-dependent hydrolysis of ATP and dATP occurred at nearly equivalent rates, whereas the rates of hydrolysis of GTP, ITP, CTP, and UTP ranged from 16-33% of that for ATP. All of the above nucleotides also supported Ca2+ transport into SR vesicles; dATP was somewhat more effective than ATP while GTP, ITP, CTP, and UTP ranged from 28-30% of the activity for ATP. In the presence of oxalate, the initial rate of Ca accumulation with dATP was 4-fold higher than for ATP, whereas the activity for GTP, ITP, CTP, and UTP ranged from 35-45% of that for ATP. For the SL membranes, Ca-activated dATP hydrolysis occurred at 60% of the rate for ATP; GTP, ITP, CTP, and UTP were hydrolyzed by the SL preparations at only 7-9% of the rate for ATP. NTP-dependent Ca2+ uptake in SL membranes was supported only by ATP and dATP, with dATP 60% as effective as ATP. GTP, ITP, CTP, and UTP did not support the transport of Ca2+ by SL vesicles. The results indicate that the SL and SR membranes contain distinctly different ATP-dependent Ca2+ transport systems.
D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002417:Cattle; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D006352:Heart Ventricles / Q000201:enzymology; D007425:Intracellular Membranes / Q000201:enzymology*; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D012265:Ribonucleotides; D012508:Sarcolemma / Q000201:enzymology*; D013379:Substrate Specificity
D012265:Ribonucleotides; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium