Characterization of Ca(2+)-stimulated adenosine 5'-triphosphatase and Ca2+ sequestering in rat liver nuclei.
The role of Ca(2+)-stimulated adenosine 5'-triphosphatase (Ca(2+)-ATPase) in Ca2+ sequestering of rat liver nuclei was investigated. Ca(2+)-ATPase activity was calculated by subtracting Mg(2+)-ATPase activity from (Ca(2+)-Mg2+)-ATPase activity. Ca2+ uptake and release were determined with a Ca2+ electrode. Nuclear Ca(2+)-ATPase activity increased linearly in the range of 10-40 microM Ca2+ addition. With those concentrations, Ca2+ was completely taken up by the nuclei dependently on ATP (2 mM). Nuclear Ca(2+)-ATPase activity was decreased significantly by the presence of arachidonic acid (25 and 50 microM), nicotinamide-adenine dinucleotide (NAD+; 2 mM) and zinc sulfate (2.5 and 5.0 microM). These reagents caused a significant decrease in the nuclear Ca2+ uptake and a corresponding elevation in Ca2+ release from the nuclei. Moreover, calmodulin (10 micrograms/ml) increased significantly nuclear Ca(2+)-ATPase activity, and this increase was not seen in the presence of trifluoperazine (10 microM), an antagonist of calmodulin. The present findings suggest that Ca(2+)-ATPase plays a role in Ca2+ sequestering by rat liver nuclei, and that calmodulin is an activator. Moreover, the inhibition of Ca(2+)-ATPase may evoke Ca2+ release from the Ca(2+)-loaded nuclei.
Yamaguchi
M
M
Laboratory of Metabolism and Endocrinology, Graduate School of Nutritional Sciences, University of Shizuoka, Japan.
Oishi
K
K
D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000502:physiology*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D009243:NAD / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013431:Sulfates / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology; D017967:Zinc Compounds / Q000494:pharmacology; D019287:Zinc Sulfate
D002147:Calmodulin; D013431:Sulfates; D017967:Zinc Compounds; D009243:NAD; D014268:Trifluoperazine; D016718:Arachidonic Acid; D019287:Zinc Sulfate; D000252:Calcium-Transporting ATPases; D002118:Calcium