Rapid refilling of Ca2+ stores in macrophages stimulated by ATP involves the sequential activation of phospholipase D and protein kinase C.
Ca2+ movements between intracellular stores, the cytoplasm and external solution were analysed in murine peritoneal macrophages stimulated by various agonists. The Ca2+ content of intracellular stores was estimated from the amplitude of Ca(2+)-transients elicited by ionomycin applied in Ca(2+)-free solution. Both uridine 5'-triphosphate (UTP) and platelet-activating factor (PAF) triggered the release of Ca2+ followed by a sustained influx, during which intracellular stores remained totally empty. In contrast, in the continuous presence of adenosine 5'-triphosphate (ATP), Ca2+ was initially released and then rapidly sequestered again by the stores. ATP-induced store refilling was not related to cell depolarization or to an increase in the intracellular Na+ concentration (two specific consequences of ATP stimulation which are not induced by PAF and UTP). Store refilling was not caused by a signal that ATP would fail to induce (e.g. as a result of receptor desensitization), but was positively controlled by ATP, even in the simultaneous presence of a concentration of PAF which, on its own, would have caused a persistent store depletion. The hypothesis that the signal delivered by ATP involves the sequential activation of phospholipase D and protein kinase C is consistent with the present pharmacological evidence. However, although we found conditions in which Ca2+ stores did not refill in the presence of ATP, this maintained store depletion was not accompanied by a sustained Ca2+ response similar to that elicited by PAF or UTP, suggesting that store depletion is a condition which is necessary, but not sufficient, for inducing Ca2+ influx.
Alonso-Torre
S R
SR
Laboratoire de Neurobiologie, CNRS URA 1857, Ecole Normale Supéieure, Paris, France.
Trautmann
A
A
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010712:Phosphatidic Acids / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology
D010712:Phosphatidic Acids; D010972:Platelet Activating Factor; D015759:Ionomycin; D000255:Adenosine Triphosphate; D012964:Sodium; D011493:Protein Kinase C; D010739:Phospholipase D; D002118:Calcium; D014544:Uridine Triphosphate