Involvement of the cyclic GMP pathway in the superoxide-induced IP3 formation in vascular smooth muscle cells

Objective To investigate whether cGMP or cAMP signal pathway is indirectly involved in the effect of superoxide on the IP3 formation in vascular smoot h muscle cells (SMC) from rat mesenteric arteries. Methods Cultured smooth muscle cells from rat mesenteric arteries were prel abelled with myo-(2-H-3) inositol for evaluation of IP3 formation, Quantita tive cAMP and cGMP levels were determined using cAMP [H-3] or cGMP [I-125] assay systems. Results In the present study, it was found that superoxide significantly in hibited the basal level of cGMP and also suppressed the sodium nitroprussid e (SNP)-induced cGMP formation in SMCs from rat mesenteric arteries. The in hibitory effect of superoxide on basal level of cGMP was similar in the abs ence or presence of ODQ (a guanylyl cyclase inhibitor). Moreover, the super oxide-induced increase in IP3 formation was significantly inhibited by SNP or s-nitroso-n-acetylpenicillamine but was significantly potentiated by ODQ or KT5823 (a cGMP-dependent protein kinase inhibitor). Superoxide had no e ffect on the basal or on the forskolin-induced cAMP production and the inhi bition of adenylyl cyclase or cAMP-dependent protein kinase did not affect the superoxide-enhanced IP3 formation. Conclusion The decreased cross-inhibition of IP3 pathway by cGMP may contri bute to the superoxide-enhanced IP3 formation in SMCs from mesenteric arter ies, The cross-talk between cGMP and IP3 pathways provides a novel mechanis m for the signalling role of superoxide in vascular SMCs. J Hypertens 2000, 18:1057-1064 (C) Lippincott Williams & Wilkins.