Prostaglandin E 2 in the salivary glands of the female tick, Amblyomma americanum (L.): calcium mobilization and exocytosis

Abstract

A cholera toxin-sensitive, prostaglandin E 2 (PGE 2) specific receptor has been identified in the plasma membrane fraction of tick salivary glands. In the present study, we report that stimulation of dispersed salivary glands of the lone star tick Amblyomma americanum (L.) with 1 nM to 10 μM PGE 2 increased the intracellular concentration of inositol trisphosphate (IP 3) in a dose-dependent manner. Incubation of dispersed tissue with 1 nM to 10 μM PGE 2 also stimulated release of 45Ca 2+ from preloaded tissue. PGE 2 (10 μM) did not stimulate an influx of 45Ca 2+. Therefore, the PGE 2 receptor in the salivary glands appears to activate a phosphoinositide phospholipase C signalling pathway to increase formation of intracellular IP 3 and, thus, mobilize Ca 2+ from intracellular stores. Incubation of dispersed salivary glands with 1 nM to 1 μM PGE 2 stimulated secretion of anticoagulant protein, but not at <1 nM or >1 μM PGE 2. In addition, the mammalian PGE 2 EP1 receptor antagonist AH-6809 affected secretion of anticoagulant by dispersed salivary gland tissue at a low concentration supporting the hypothesis that the PGE 2 receptor in tick salivary glands is EP1-like. We propose that a major function for PGE 2 in tick salivary glands is to mobilize Ca 2+ and stimulate secretion (exocytosis) of bioactive proteins into the tick's saliva during feeding.