NITRIC-OXIDE SYNTHASE AND ARGINASE IN CELLS ISOLATED FROM THE RAT GASTRIC-MUCOSA

Nitric oxide (NO) synthase activity, which converts arginine to citrul line and NO, is present in homogenates of rat gastric mucosal cells. T he aims of this study were to identify the form of NO synthase express ed in gastric cells isolated from fed rats, and to investigate the met abolism of arginine by suspensions of intact mucosal cells. Antibodies directed against the neuronal form of NO synthase recognised a protei n of 160 kDa on immunoblots of extracts of gastric cells, and stained isolated cells of approx. 8 mu m in diameter. NO synthase was enriched in a cell fraction which banded at high-density in a Percoll gradient , and was inhibited (IC50) by N-G-nitro-L-arginine (0.8 mu M), N-G-mon omethyl-L-arginine (12.6 mu M), L-canavanine (147 mu M), trifluoperazi ne (140 mu M) and by phosphorylation involving protein kinase C. Intac t gastric cells converted exogenous arginine to ornithine and citrulli ne. Arginase was present in the cells, and was predominantly responsib le for arginine metabolism because formation of ornithine and citrulli ne was reduced by the arginase inhibitors, N-G-hydroxy-L-arginine and L-ornithine, but not by NO synthase inhibitors such as N-G-nitro-L-arg inine. In conclusion, NO synthase that resembles the neuronal isoform is present in gastric mucosal cells, but a pathway involving arginase seems to be largely responsible for citrulline formation from exogenou s arginine in intact mucosal cells.