Summary

formyl peptide receptors mediate increases in the cytosolic Ca2 concentration ([Ca21) via pertussis toxin-sensitive G pro-teins of the G family. We compared the effects of 2-(3-chloro-phenyl)-histamine (CPH) [2-[2-(3-chlorophenyl)-1 H-imidazol-4-yI] ethanamine], one of the most potent and selective H1 receptor agonists presently available, with those of histamine and N-formyl-L-methionyl-L-Ieucyl-L-phenylalanine (fMLP) in these cells. CPH increased [Ca21 through Ca2 mobilization and Ca2 influx. Unlike histamine-induced rises in [Ca2], those induced by CPH were not desensitized in a homologous manner, and there was no cross-desensitization between CPH and histamine. Like fMLP, CPH activated phospholipases C and D, tyrosine phos-phorylation, superoxide anion formation, and azurophilic granule release. The effects of CPH on [Ca2j, phospholipase D, and superoxide anion formation were inhibited by pertussis toxin