Functional neurokinin NK-1 receptor expression in rat peritoneal mast cells

Objective and Design: Recently, Ogawa et al. [17] reported that the peritoneal mast cells (PMCs) of rats can release histamine by substance P (SP) in a receptor-dependent manner. In the present study, we confirmed and extended their findings.¶Material: PMCs were isolated from six strains of rats. In some experiments, peritoneal cells in the non-MC fraction were used.¶Methods: PMCs were incubated with SP, neurokinin (NK) receptor agonists or antagonists, and histamine content in the supernatant was measured. In the binding assay, PMCs were incubated with [125I]BH-SP together with SP or NK receptor antagonists. NK-1 receptor mRNA was detected using a reverse transcription-polymerase chain reaction (RT-PCR) assay.¶Results: PMCs from Slc:Wistar and F344/NSlc were highly sensitive to SP, leading to histamine release, whereas those from Slc:SD and three other strains were not. PMCs from Slc:Wistar and F344/NSlc also released histamine in the presence of an NK-1 agonist. The histamine release induced by SP and the NK-1 agonist was inhibited by the NK-1 receptor antagonists, FK888 and CP-99,994. [125I]BH-SP binding experiments revealed that PMCs from Slc:Wistar rats possessed a single high affinity binding site for SP and that the binding was blocked by NK-1 receptor antagonists. Peritoneal cells in the non-MC fraction exhibited no appreciable binding. In the RT-PCR assay, expression of NK-1 receptor mRNA was evident in Slc:Wistar PMCs, but not in the non-MC fraction from Slc:Wistar or Slc:SD PMCs.¶Conclusion: These data demonstrate the existence of functional NK-1 receptors on freshly isolated PMCs in at least some strains of rats.