ATP stimulates Ca2+ uptake and increases the free Ca2+ concentration in isolated rat liver nuclei.
Addition of ATP to a highly purified fraction of rat liver nuclei incubated with submicromolar concentrations of Ca2+ and trace amounts of 45Ca2+ resulted in the rapid accumulation of 45Ca2+ in the nuclei. This was associated with an increase in intranuclear free Ca2+ concentration as measured with the fluorescent dye 1-[2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy]-2-(2'-a mino-5'- methylphenoxy)ethane-N,N,N',N'-tetraacetic acid (fura-2). Inhibitors of microsomal and mitochondrial Ca2+ translocases had no effect on nuclear Ca2+ sequestration, indicating that it was distinct from previously known intracellular Ca2+-transporting systems. Ca2+ uptake and the associated increase in intranuclear free Ca2+ concentration were prevented by calmidazolium, a potent calmodulin antagonist. Partial characterization of the ATP-stimulated nuclear Ca2+ uptake showed that maximal rates of Ca2+ uptake and increase in intranuclear free Ca2+ level occurred at concentrations of Ca2+ normally present in the cytosol of mammalian cells. Together, these results show that a distinct, ATP- and calmodulin-dependent Ca2+ uptake system exists in liver nuclei. This system may play an important role in the regulation of intranuclear Ca2+-dependent processes.
Nicotera
P
P
Department of Toxicology, Karolinska Institutet, Stockholm, Sweden.
McConkey
D J
DJ
Jones
D P
DP
Orrenius
S
S
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008856:Microscopy, Fluorescence; D051381:Rats; D011919:Rats, Inbred Strains
D002147:Calmodulin; D007093:Imidazoles; C031938:calmidazolium; D000255:Adenosine Triphosphate; D002118:Calcium