Nitric oxide synthase and cGMP activity in the salivary glands of the American dog tick Dermacentor variabilis

We colocalized nitric oxide synthase (NOS) activity in epithelial cells tha t surround the salivary gland duct in female Dermacentor variabilis with NA DPH diaphorase histochemistry and immunohistochemistry using a polyclonal a ntiendothelial NOS. Using size-exclusion chromatography, a fraction with a molecular mass of about 185 kDa that had diaphorase activity was eluted fro m tick; salivary gland homogenate. This fraction converted arginine to citr ulline with the production of nitric oxide (NO), which was detected by usin g electron spin resonance spectroscopy. The complete activity of the diapho rase fraction was dependent on NADPH, FAD, tetrahydrobiopterin, calmodulin, (CaM), and Ca2+, but was not dependent on dithiothreitol. The arginine ana log N-G-monomethyl-L-arginine inhibited the activity of this fraction. NO a nd arginine activated soluble guanylate cyclase to produce cGMP in dopamine -stimulated isolated salivary glands. Dopamine-stimulated isolated salivary glands treated with tick saline containing either EDTA, the NOS inhibitor N-G-nitro-L-arginine methyl ester, or the calcium/CaM binding inhibitor W-7 showed no increase in cGMP. The NO donor sodium nitroprusside significantl y increased cGMP levels in unstimulated isolated salivary glands. A possibl e function for NO in salivation by this ixodid tick is discussed. (C) 2000 Academic Press.