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  • Title: Inhibition of nitric oxide synthase activity in dispersed gastric muscle cells by protein kinase C.
    Author: Murthy KS, Jin JG, Makhlouf GM.
    Journal: Am J Physiol; 1994 Jan; 266(1 Pt 1):G161-5. PubMed ID: 7508198.
    Abstract:
    The present study examined whether NO synthase (NOS) activity in gastric muscle cells was inhibited by protein kinase C (PKC). Vasoactive intestinal peptide (VIP) increased L-[3H]citrulline production (a coproduct and index of NO synthesis) in muscle strips (81.9 +/- 11.6%) and dispersed muscle cells (80.9 +/- 4.6%) of rabbit stomach. Cholecystokinin octapeptide (CCK-8), carbachol, and phorbol 12-myristate 13-acetate (PMA) inhibited VIP-induced L-[3H]citrulline production in muscle cells and muscle strips; the inhibition was reversed by pretreatment with the PKC inhibitor, calphostin C. The Ca(2+)-mobilizing agents, CCK-8, acetylcholine, ionomycin, and KCl, all of which increased PKC activity in dispersed muscle cells, did not increase L-[3H]citrulline production. After treatment of the cells with calphostin C, all four agents stimulated L-[3H]citrulline production, although to a lesser extent than VIP (approximately 50%). VIP-induced relaxation of basal but not carbachol-stimulated tension was accompanied by increase in L-[3H]citrulline production and was inhibited by the NOS inhibitor NG-nitro-L-arginine (L-NNA). Preincubation of carbachol-treated muscle strips with calphostin C restored the ability of VIP to stimulate L-[3H]citrulline production and the ability of L-NNA to inhibit VIP-induced relaxation. We conclude that 1) VIP-stimulated NOS activity is inhibited by agents that increase PKC activity in gastric smooth muscle cells, and 2) agents that increase both cytosolic free Ca2+ concentration and PKC activity stimulate NOS activity only when PKC activity is suppressed.
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