Differential activation of nitric oxide synthase through muscarinic acetylcholine receptors in rat salivary glands

Muscarinic receptors play an important role in secretory and vasodilator re sponses in rat salivary glands. Nitric oxide synthase (NOS) appears to be o ne of the multiple effecters coupled to muscarinic receptors in both subman dibular and sublingual glands although some differences have been found dep ending on the gland studied. First, submandibular glands had a lower basal activity of nitric oxide synthase than sublingual glands and the concentrat ion-response curve for carbachol was bell-shaped in the former but not in s ublingual glands. Second, cGMP levels displayed a similar profile to that o bserved for NOS activity in both glands. Third, protein kinase C also coupl ed to muscarinic receptor activation in the glands might have a regulatory effect on nitric oxide production since its activity was higher in basal co nditions in submandibular than sublingual glands and it also increased in t he presence of the agonist at a concentration that inhibited NOS activity i n submandibular glands. The effects appear to be partly related to the expr ession of a minor population of M-1 receptors in submandibular glands absen t in sublingual as determined in binding and signaling experiments with the muscarinic receptor antagonist pirenzepine. (C) 2000 Elsevier Science B.V. All rights reserved.