The tick Dermacentor variabilis returns much of the water and ions from the bloodmeal back into the host as saliva produced in paired salivary glands. These glands are made up of acini and a system of ducts (Fig. 1). Bloodsucking alternates with salivation, but saliva is constantly produced by the acini and expelled into the ducts where it accumulates during bloodsucking. Ducts consist of a layer of epithelial cells, a cuticular coil, and an epicuticular lining of the lumen (Figs. 2, 3). Actin-like filaments run from the coil into the epithelial cells as shown by TEM and CLSM (Figs. 3, 4). These filaments are absent in cytochalasin D treated ducts.
Nitric oxide synthase (=NADPH diaphorase) is present in duct epithelial cells as shown by histochemistry (Fig. 5). We measured nitric oxide (NO) indirectly by the conversion of L-arginine to L-citrulline. NO production and production of saliva is dopamine dependent. NO activates guanylyl cyclase as measured by an RIA for cGMP. The lumen width in dopamine stimulated isolated ducts increased by 19.7% as measured optically. Ducts pre-treated with 10 μM L-NAME, an NOS specific inhibitor, showed no significant increase in width. The addition of 10 μM L-arginine to these ducts partially restored the increase in lumen diameter.