Differential induction of nitric oxide synthase in rat gastric and vascular smooth muscle tissue: Distinct tissue distribution and distinctive signaling pathways

In rat aorta rings (RA) and in gastric circular muscle (CM) and gastric lon gitudinal muscle (LM) preparations maintained in vitro, inducible nitric ox ide synthase (iNOS) induction was monitored functionally (1 mM L-arginine-i nduced relaxation), biochemically (appearance of iNOS mRNA), and immunohist ochemically. Functional iNOS (L-arginine-mediated relaxation) was induced i n RA and CM tissues (but NOT in the LM preparation) over 2 to 5 h. iNOS ind uction was detected by immunocytochemistry in RA smooth muscle elements and in macrophage-like cells in CM. Functional iNOS induction correlated with iNOS mRNA induction. In the RA and CM, functional iNOS induction was blocke d by both actinomycin D and cycloheximide; actinomycin D also blocked the a ppearance of iNOS mRNA in both tissues. In contrast, cycloheximide blocked CM (but not RA) iNOS mRNA induction. In CM tissue, functional iNOS inductio n was not affected by genistein, tyrphostin 47/AG213, or vanadate. But, in the RA, both genistein and tyrphostin 47/AG213 blocked the appearance of fu nctional iNOS; neither inhibitor prevented the appearance of RA iNOS mRNA. Vanadate, in the RA tissue, blocked both the appearance of iNOS mRNA and th e induction of functional iNOS. In RA tissue, but not in the CM, inhibitors of NF-kappa B activation blocked the appearance of both functional iNOS an d iNOS mRNA. We conclude that in different smooth muscle preparations (aort a versus gastric), there can be a differential induction of iNOS mRNA and " functional" iNOS not only in different cellular elements but also in terms of different signaling pathways.