POSSIBLE INVOLVEMENT OF NITRIC-OXIDE IN CARBACHOL-INDUCED ACTIVATION OF TRANSGLUTAMINASE IN RAT SUPERIOR CERVICAL SYMPATHETIC-GANGLIA

The addition of a muscarinic agonist, carbachol (Carb, 0.1 mM), to a physiological medium markedly increased Ca2+-dependent transglutaminase (TG) activity (approximately 10-fold) in isolated rat superior cervical sympathetic ganglia (SCG) following in vitro aerobic incubation for 30 min at 37 degrees C. The Carb-evoked stimulation of ganglionic TG activity was considerably reduced (-51%) in the presence of N-G-monomethyl-L-arginine (L-NMMA, 50 mu M), a selective inhibitor of nitric oxide (NO) synthase. While the suppressant effect of L-NMMA was completely eliminated by the addition of an excess concentration of L-arginine (0.5 mM), a precursor of NO. These observations imply that Carb-induced TG activation possibly involves NO mediation in SCG tissue. The Carb-induced elevation in ganglionic TG activity was markedly reduced (-84%) at as early as 15 min of incubation in the medium containing hemoglobin (Hb) (20 mu M), an agent that scavenges only extracellular NO gas. Thus, it is evident that a large fraction of NO released from inside the neuronal cells to extracellular space could rapidly diffuse back into the same group of cells to induce activation of the tissue TG. Methylene blue (MB), an inhibitor of soluble guanylate cyclase (GC), at 0.5 mM, a concentration which is effective in almost abolishing the Carb-evoked synthesis of cyclic GMP (cGMP), had no effect on ganglionic TG activation induced by Carb. Therefore, an increase in cGMP synthesis mediated by NO might not participate in NO-dependent ganglionic TG activation following the stimulation with Carb. Neither actinomycin D (AMD) (1.0 mu g/ml) nor cycloheximide (CHX) (10 mu g/ml) caused an apparent change in Carb-evoked ganglionic TG activity. A potent inhibitor of endonuclease, aurintricarboxylic acid (ATA) (0.1 mM), led to a slight but statistically insignificant decrease (-25%) in Carb-evoked TG activation. These results suggest that the NO-mediated TG activation during synaptic transmission via muscarinic cholinergic receptors in ganglia is unlikely to be accompanied by DNA cleavage, which leads to cell degradation.