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

The effects of,a soluble guanylyl cyclase (sGC) activator, 3-(5 ' -hydroxym ethyl-2 ' -furyl)-1-benzyl indazole (YC-1), on formylmethionyl-leucyl-pheny lalanine (fMLP)-stimulated [Ca2+](i) elevation in rat neutrophils were exam ined. YC-1 produced a concentration-dependent inhibition of [Ca2+](i) eleva tion. 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+ infl ux. YC-1 also inhibited active and passive Mn2+ influx, and this inhibitory effect was not attenuated by the sGC inhibitor 6-anilino-5,8-quinolinequin one (LY83583). Sodium nitroprusside did not affect the fMLP-stimulated [Ca2 +](i) changes. Pretreatment of neutrophils with the cyclic GMP-dependent pr otein kinase inhibitor 8-(4-chlorophenylthio) guanosine-3 ' ,5 ' -monophosp horothioate, Rp-isomer (Rp-8-pCPT-cGMPS), LY83583, the protein phosphatase 2B inhibitor cyclosporin A, or the protein kinase inhibitor staurosporine d id not attenuate the inhibition of [Ca2+](i) by YC-1. YC-1 inhibited the fM LP-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 i s mainly via the blockade of Ca2+ entry through the inhibition of tyrosine kinase activity, but not the stimulation of protein kinase C and protein ph osphatase 2B. (C) 2001 Elsevier Science Inc. All rights reserved.