Tick salivary glands and saliva contain extremely high levels of prostaglandin E2 (PGE2) and PGF2? which are likely important in tick feeding. Data also demonstrate that PGE2 functions as a local hormone in ixodid tick salivary gland physiology. A PGE2-specific receptor was identified in the salivary gland plasma membrane that exhibits a single, high affinity PGE2 binding site, is saturable, reversible, specific for PGE2 and is coupled to a cholera toxin-sensitive guanine nucleotide regulatory protein. PGE2 directly activates phospholipase C and stimulates inositol triphosphate (IP3) formation in dispersed salivary gland acini and stimulates an efflux of Ca 2+ from pre-labeled salivary glands. Functionally, PGE2 stimulates release of salivary gland anticoagulant protein in preference to PGF2? or the thromboxane analog U-46619 in accordance with their respective binding affinities for the PGE2 receptor. TMB-8, an antagonist of intracellular IP3 receptors inhibits PGE2 stimulated protein secretion. Phorbol ester, an activator of Ca 2+ requiring protein kinase C (PKC) stimulated secretion of salivary gland protein in a dose-dependent manner, suggesting that PKC is a regulator of Ca 2+ -dependent exocytosis. The results support the hypothesis that PGE2 stimulates secretion of tick salivary gland protein via a phosphoinositide signaling pathway, mobilization of intracellular Ca 2+ and activation of PKC.

Index terms: exocytosis, protein kinase C, calcium