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Prostaglandin E2-stimulated secretion of protein in the salivary glands of the lone star tick via a phosphoinositide signaling pathway

Department of Entomology and Plant Pathology, Oklahoma State University, 74078-3033, Stillwater, OK, USA.
Insect Biochemistry and Molecular Biology (Impact Factor: 3.42). 11/2000; 30(11):1099-106. DOI: 10.1016/S0965-1748(00)00087-4
Source: PubMed

ABSTRACT Previous studies identified a prostaglandin E(2) (PGE(2)) receptor in the salivary glands of partially fed female lone star ticks, Amblyomma americanum (L.). In the present studies, protein secretion from dispersed salivary gland acini was shown to be specific for PGE(2), as compared with PGF(2alpha) or the thromboxane analog U-46619, in accordance with their respective binding 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-23187 (1 to 100 microM) stimulated secretion of anticoagulant protein in a dose-dependent manner but the voltage-gated Ca(2+)-channel blocker verapamil (1 to 1000 microM) and the receptor-mediated Ca(2+)-entry antagonist, SK&F 96365 (1 and 10 microM), and 5mM ethylene glycol bis(beta-aminoethyl ether)-N,NN', N'-tetraacetic acid (EGTA) had no appreciable effect on inhibiting PGE(2)-stimulated secretion of anticoagulant protein. PGE(2) (0.1 microM) and the non-hydrolyzable analog of guanosine triphosphate (GTP), GTPgammaS (10 microM), directly activated phospholipase C (PLC) in a membrane-enriched fraction of the salivary glands after PLC was first incubated with the PGE(2) EP1 receptor antagonist AH-6809, which presumably antagonized endogenous PGE(2) (0.3 microM) in the broken-cell-membrane-enriched fraction. TMB-8, an antagonist of intracellular inositol trisphosphate (IP(3)) receptors, inhibited PGE(2)-stimulated secretion. The results support the hypothesis that PGE(2) stimulates secretion of tick salivary gland protein via a phosphoinositide signaling pathway and mobilization of intracellular Ca(2+).

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    • "Qian et al. (1997) reported on a specific PGE 2 receptor in the salivary glands of the female tick, Amblyomma americanum, which acts in modulating salivary secretion . Another PGE 2 receptor may regulate protein secretion in the salivary glands (Yuan et al., 2000). Aside from this, we have very little understanding of PG actions at the level of insect cells. "
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    • "Further work indicated that the PGE 2 receptor stimulates secretion of protein in salivary glands of female ticks. Yuan et al. (2000) inferred from their results that PGE 2 acts through a G protein coupled EP1 receptor. Aside from this work with tick salivary glands, however, there is no information on the mechanisms of eicosanoid actions in invertebrates. "
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    • "Dental caries, resulting from the loss of salivary flow, may be associated with periodontal disease (Ravald and List, 1998). Prostaglandins (PGs) are among the most relevant local mediators that participate in the modulation of acinar cell functions under basal conditions (Yuan et al., 2000). During inflammation or in early stages of autoimmune diseases, PGs are released in large amounts. "
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