Prostaglandin E-2-stimulated secretion of protein in the salivary glands of the lone star tick via a phosphoinositide signaling pathway

Previous studies identified a prostaglandin E-2 (PGE(2)) receptor in the sa livary glands of partially fed female lone star ticks, Amblyomma americanum (L.). In the present studies, protein secretion from dispersed salivary gl and acini was shown to be specific for PGE(2), as compared with PGF(2 alpha ) or the thromboxane analog U-46619, in accordance with their respective bi nding affinities for the PGE(2) receptor. Furthermore, the selective PGE(2) EP1 receptor agonist, 17-phenyl trinor PGE(2), was as effective as PGE(2) in stimulating secretion of anticoagulant protein. Calcium ionophore A-2318 7 (1 to 100 mu M) stimulated secretion of anticoagulant protein in a dose-d ependent manner but the voltage-gated Ca2+-channel blocker verapamil (1 to 1000 mu M) and the receptor-mediated Ca2+-entry antagonist, SK&F 96365 (1 a nd 10 mu M), and 5 mM ethylene glycol bis(beta-aminoethyl ether)-N,NN',N'-t etraacetic acid (EGTA) had no appreciable effect on inhibiting PGE(2)-stimu lated secretion of anticoagulant protein. PGE(2) (0.1 mu M) and the nonhydr olyzable analog of guanosine triphosphate (GTP), GTP gamma S (10 mu M), dir ectly activated phospholipase C (PLC) in a membrane-enriched fraction of th e salivary glands after PLC was first incubated with the PGE(2) EP1 recepto r antagonist AH-6809, which presumably antagonized endogenous PGE(2) (0.3 m u M) in the broken-cell-membrane-enriched fraction. TMB-8, an antagonist of intracellular inositol trisphosphate (IP3) receptors, inhibited PGE(2)-sti mulated secretion. The results support the hypothesis that PGE(2) stimulate s secretion of tick salivary gland protein via a phosphoinositide signaling pathway and mobilization of intracellular Ca2+. (C) 2000 Elsevier Science Ltd. All rights reserved.