Inhibition of extracellular Ca2+ entry by YC-1, an activator of soluble guanylyl cyclase, through a cyclic GMP-independent pathway in rat neutrophils

Abstract

The effects of a soluble guanylyl cyclase (sGC) activator, 3-(5′-hydroxymethyl-2′-furyl)-1-benzyl indazole (YC-1), on formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated [Ca2+]i elevation in rat neutrophils were examined. YC-1 produced a concentration-dependent inhibition of [Ca2+]i elevation. Pretreatment of neutrophils with YC-1 did not enhance its inhibitory effect. YC-1 also inhibited the [Ca2+]i changes caused by ionomycin. In a biphasic model, measuring the [Ca2+]i stimulation by fMLP in a Ca2+-free medium followed by reintroduction of Ca2+, YC-1 mainly affected Ca2+ influx. YC-1 also inhibited active and passive Mn2+ influx, and this inhibitory effect was not attenuated by the sGC inhibitor 6-anilino-5,8-quinolinequinone (LY83583). Sodium nitroprusside did not affect the fMLP-stimulated [Ca2+]i changes. Pretreatment of neutrophils with the cyclic GMP-dependent protein kinase inhibitor 8-(4-chlorophenylthio) guanosine-3′,5′-monophosphorothioate, Rp-isomer (Rp-8-pCPT-cGMPS), LY83583, the protein phosphatase 2B inhibitor cyclosporin A, or the protein kinase inhibitor staurosporine did not attenuate the inhibition of [Ca2+]i by YC-1. YC-1 inhibited the fMLP-stimulated protein tyrosine phosphorylation. These results indicate that cyclic GMP does not play an important role in the regulation of [Ca2+]i in rat neutrophils. Inhibition of fMLP-stimulated [Ca2+]i changes by YC-1 is mainly via the blockade of Ca2+ entry through the inhibition of tyrosine kinase activity, but not the stimulation of protein kinase C and protein phosphatase 2B.