A specific prostaglandin E-2 receptor and its role in modulating salivary secretion in the female tick, Amblyomma americanum (L)

Prostaglandins of the 2-series (e.g. PGE(2)) are typically synthesized from arachidonic acid (AA) after AA is released from cellular phospholipids after activation of an intracellular phospho- lipase A(2) (PLA(2)). Treatment of isolated salivary glands with PLA(2) inhibitor oleyloxyethyl phosphorylcholine (OPC) or prostaglandin synthetase inhibitors reduced dopamine-induced fluid secretion and cyclic AMP (cAMP) levels in isolated salivary glands, PGE(2) and its analog, 17-phenyl trinor PGE(2), partly reversed the inhibition of secretion and cAMP; level by OPC, suggesting that prostaglandins may have an autocrine effect in modulating tick salivary gland function, A specific PGE(2) receptor was identified in the plasma membrane fraction of the salivary glands, The receptor exhibits a single, high affinity PGE(2) binding site with a K-D approximate to 29 nM, is saturable, reversible, and specific for PGE(2) and coupled to a cholera toxin-sensitive guanine nucleotide regulatory protein, Assay of adenylate cyclase activity in salivary gland membranes showed that PGE(2) neither stimulated nor inhibited adenylate cyclase activity, indicating that the PGE(2) effects on cAMP levels and possibly secretion are indirect, and that the PGE(2) receptor stimulates an alternate ''second messenger'' pathway. (C) 1997 Elsevier Science Ltd.