The response to ATP of peritoneal macrophages from wild-type (WT) and P2X 7 -invalidated (KO) mice was tested. Low concentrations (1-100 μM) of ATP transiently increased the intracellular concentration of calcium ([Ca 2+ ] i ) in cells from both mice. The inhibition of the polyphosphoinositide-specific phospholipase C with U73122 inhibited this response especially in WT mice suggesting that the responses coupled to P2Y receptors were potentiated by the expression of P2X 7 receptors. One millimolar ATP provoked a sustained increase in the [Ca 2+ ] i only in WT mice. The response to 10 μM ATP was potentiated and prolonged by ivermectin in both mice. One millimolar ATP increased the influx of extracellular calcium, decreased the intracellular concentration of potassium ([K + ] i ) and stimulated the secretion of interleukin-1β (IL-1β) only in cells from WT mice. Ten micromolar ATP in combination with 3 μM ivermectin reproduced these responses both in WT and KO mice. The secretion of IL-1β was also increased by nigericin in WT mice and the secretory effect of a combination of ivermectin with ATP in KO mice was suppressed in a medium containing a high concentration of potassium. In WT mice, 150 μM BzATP stimulated the uptake of YOPRO-1. Incubation of macrophages from WT and KO mice with 10 μM ATP resulted in a small increase of YOPRO-1 uptake, which was potentiated by addition of 3 μM ivermectin. The uptake of this dye was unaffected by pannexin-1 blockers. In conclusion, prolonged stimulation of P2X 4 receptors by a combination of low concentrations of ATP plus ivermectin produced a sustained activation of the non-selective cation channel coupled to this receptor. The ensuing variations of the [K + ] i triggered the secretion of IL-1β. Pore formation was also triggered by activation of P2X 4 receptors. Higher concentrations of ATP elicited similar responses after binding to P2X 7 receptors. The expression of the P2X 7 receptors was also coupled to a better response to P2Y receptors.

ATP in the 100 μM-1 mM concentration range provoked a calcium-independent increase of the oxidation of dichlorodihydrofluorescein (DCFH) to dichlorofluorescein (DCF) by mouse submandibular cells. 3′-O-(4-benzoyl) benzoyl adenosine 5′-triphosphate (BzATP), a P2X 7 agonist, but not a muscarinic or an adrenergic agonist, reproduced the effect of ATP. The inhibition of phospholipase C by U73122 or the potentiation of P2X 4 receptor activation with ivermectin did not modify the response to ATP. ATP did not increase the oxidation of DCFH in cells isolated from submandibular glands of P2X 7 knockout mice or in cells pretreated with a P2X 7 antagonist. The inhibition of protein kinase C or of mitogen-activated protein kinase (MAP kinase) or of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase blocked the oxidation of DCFH without affecting the increase of the intracellular concentration of calcium or the uptake of ethidium bromide in response to extracellular ATP. From these results it is concluded that the activation of the P2X 7 receptors from submandibular glands triggers an intracellular signalling cascade involving protein kinase C and MAP kinase leading to the stimulation of NADPH oxidase and the subsequent generation of reactive oxygen species.