Peritoneal macrophages were isolated from wild type (WT) mice and from mice invalidated for the P2X(7) receptor (KO) which had been pretreated with thioglycolate. In cells from WT mice, 1 mM
ATP increased the intracellular concentration of
calcium ([Ca(2+)](i)), the uptake of
ethidium bromide, the production of
reactive oxygen species (ROS), the secretion of IL-1beta, the release of
oleic acid and of
lactate dehydrogenase; it decreased the intracellular concentration of
potassium ([K(+)](i)). In KO mice,
ATP transiently increased the [Ca(2+)](i) confirming that the P2X(7) receptor is a major receptor of peritoneal macrophages.
WKYMVm, an agonist of receptors for formylated
peptides (FPR) also increased the [Ca(2+)](i) in murine macrophages. The slight increase of the [Ca(2+)](i) was strongly potentiated by
ivermectin confirming the expression of functional P2X(4) receptors by murine peritoneal macrophages.
CRAMP, the unique
antimicrobial peptide derived from
cathelin in mouse inhibited all the responses coupled to P2X(7) receptors in macrophages from WT mice. Agonists for FPR had no effect on the increase of the [Ca(2+)](i) in response to
ATP.
CRAMP had no effect on the increase of the [Ca(2+)](i) evoked by a combination of
ATP and
ivermectin in macrophages from P2X(7)-KO mice. In summary
CRAMP inhibits the responses secondary to the activation of the murine P2X(7) receptors expressed by peritoneal macrophages. This inhibition is not mediated by FPR receptors and is specific since
CRAMP has no effect on the response coupled to P2X(4) receptors. It can thus be concluded that the interaction between P2X(7) receptors and
cathelin-derived
antimicrobial peptides is species-specific, in some cases (man) positive in others (mouse) negative.