Basal Mg(2+)-dependent ATPase activity of rat liver microsomes is not influenced by ambient free Ca2+.
The potent inhibitor of Ca2+, Mg(2+)-ATPase activity, thapsigargin, has been used to investigate the effect of ambient free Ca2+ on basal Mg(2+)-dependent ATPase activity in rat liver microsomes. Thapsigargin non-competitively inhibited both Ca(2+)-stimulated ATP-dependent Ca2+ uptake and Ca(2+)-stimulated Mg(2+)-dependent ATPase activity. At a concentration of 1 microM, thapsigargin completely inhibited the Ca(2+)-pump activity, without affecting Mg(2+)-dependent ATPase activity measured in the absence of Ca2+. Increasing the ambient free Ca2+ concentration did not alter the basal Mg(2+)-dependent ATPase activity. The data presented indicate that ATPase activity measured in the absence of Ca2+ is a reliable measure for the basal Mg(2+)-dependent ATPase activity and that, consequently, the Ca(2+)-stimulated Mg(2+)-dependent ATPase activity can indeed be defined as the difference between the ATPase activity measured in the presence and the absence of Ca2+.
van de Put
F H
FH
Department of Biochemistry, University of Nijmegen, The Netherlands.
Visser
G J
GJ
Donkers
E A
EA
Theuvenet
A P
AP
Willems
P H
PH
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D013729:Terpenes; D019284:Thapsigargin; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium