Biphasic and differential modulation of Ca2+ entry by ATP and UTP in promyelocytic leukaemia HL60 cells.
ATP and UTP cause mobilization of Ca2+ from the intracellular stores with similar potency in several cell types including both undifferentiated and differentiated HL60 cells. We show here that, in HL60 cells with Ca2+ stores that had been fully and irreversibly emptied using the endomembrane Ca(2+)-ATPase inhibitor thapsigargin, both nucleotides produced a biphasic effect on Ca2+ entry, first rapid inhibition and then delayed (about 15 s) activation. ATP was more effective at producing the initial inhibition of Ca2+ entry, whereas UTP was more effective at activating the delayed Ca2+ entry. Previous incubation with UTP desensitized the Ca2+ mobilization and the delayed activation of Ca2+ entry induced by ATP but not the inhibition of Ca2+ entry. The ATP analogue 2-methylthioATP (2-MeSATP) barely mobilized stored Ca2+ but inhibited Ca2+ entry. These results could be explained by the presence of two receptors: (i) a P2u receptor sensitive to ATP and UTP, responsible for activation of phospholipase C and Ca2+ mobilization, early inhibition of Ca2+ entry and delayed activation of Ca2+ entry and (ii) a P2y-like receptor sensitive to ATP and 2-MeSATP which produces only inhibition of Ca2+ entry. The inhibition of Ca2+ entry by nucleotides increased greatly during differentiation. Given that Ca2+ mobilization by nucleotides is not modified by differentiation, this suggests that a component of the mechanism of inhibition of Ca2+ entry is gradually expressed during differentiation of HL60 cells.
Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid, Spain.
M
M
Montero
J
J
Garcia-Sancho
J
J
Alvarez
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013873:Thionucleotides / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014544:Uridine Triphosphate / Q000494:pharmacology*
D013729:Terpenes; D013873:Thionucleotides; C022571:adenosine 5'-O-(3-thiotriphosphate); D008345:Manganese; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D002118:Calcium; D014544:Uridine Triphosphate; C008501:2-methylthio-ATP