Regulation of Mucin Synthesis by Neuronal Nitric Oxide Synthase in Gastric Pit Cells

We investigated the stimulatory actions of epidermal growth factor (EGF) and a cytoprotective compound, geranylgeranylacetone (GGA), on mucin synthesis of guinea pig gastric pre-pit cells, maintained in a serum-free culture system. GGA increased [3H]glucosamine uptake and accumulation of mucous granules positive for galactose oxidase-Schiff reaction in the cells. This stimulatory action of GGA was equivalent to that of EGF, whereas GGA did not stimulate cell growth. EGF and GGA increased the release of nitric oxide (NO) degeneration products, NO2- and NO3-. [3H]Glucosamine uptake by the cells was completely inhibited by the non-selective NO synthase (NOS) inhibitors, N G-nitro-L-arginine, and N G-monomethyl-L-arginine; and it was only partially inhibited by a more selective inhibitor for inducible NOS isoform, aminoguanidine. Immunoblot analysis with antibodies against three isozymes of NOS showed that GGA and EGF induced neuronal NOS but not endothelial NOS or inducible NOS. Our results suggest that GGA and EGF stimulate mucin synthesis at least in part through the NO-dependent pathway, leading to increased integrity of the gastric mucosa.