Inhibitory effects of calcitonin gene-related peptide on substance-P-induced superoxide production in human neutrophils

Abstract

We examined the mechanisms of the inhibitory effects of calcitonin gene-related peptide (CGRP) on substance-P-induced superoxide anion (O − 2) production in human neutrophils. Substance P (30 μM) caused O − 2 production associated with an inositol-1,4,5-trisphosphate (IP 3)-induced transient increase in intracellular Ca 2+ concentrations ([Ca 2+] i). CGRP (10 μM) significantly inhibited substance-P-induced O − 2 production and transient increase in [Ca 2+] i, but it only slightly suppressed IP 3 formation. In addition, CGRP inhibited IP 3-induced O − 2 production and transient increase in [Ca 2+] i caused by exogenous addition of IP 3 in saponin-permeabilized neutrophils. These findings suggest that CGRP inhibits the response of neutrophils to substance P through the inhibition of IP 3-induced Ca 2+ release from intracellular Ca 2+ stores. The inhibitory effects of CGRP on substance P- or IP 3-induced O − 2 production and increases in [Ca 2+] i were abolished by pretreating the neutrophils with a CGRP receptor antagonist, CGRP-(8–37), or cyclic AMP (cAMP)-dependent protein kinase inhibitors, N-[2-(methylamino) ethyl]-5-isoquinoline-sulfonamide dihydrochloride (H-8) and 9- n-hexyl ester derivative of K-572a (8 R,9 S,11 S)-(−)-9-hydroxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1 H,8 H,11 H-2,7b,11atriazadibenzoa(a,g)cycl (KT5720). We concluded that CGRP receptor stimulation reduces substance-P-induced O − 2 production by the inhibition of IP 3-induced transient increase in [Ca 2+] i, probably via the phosphorylation of IP 3 receptor by cAMP-dependent protein kinase.