OCTOPAMINE ENHANCES PHAGOCYTOSIS IN COCKROACH HEMOCYTES - INVOLVEMENT OF INOSITOL TRISPHOSPHATE

Octopamine and 5-hydroxytryptamine (5-HT) were previously shown to affect phagocytosis in cockroach hemocytes through unidentified receptor-mediated events. In the present study, we examined the ability of 5-HT and octopamine to enhance inositol trisphosphate (IP3) production using hemocyte membranes of the American cockroach, Periplaneta americana. Octopamine enhanced IP3 production with a maximal peak at 100 nM. Similarly, 5-HT enhanced IP3 production with a maximal effect at 10 nM. The effects of 5-HT and octopamine are not additive, suggesting that both are working through the same receptor. Phentolamine, a general octopamine antagonist, blocked the effects of octopamine and 5-HT, while a mammalian 5-HT2 antagonist that blocks 5-HT-sensitive receptors in insect peripheral tissue, ketanserin, did not. A pharmacological profile indicates that the receptor is similar to an octopamine(1)-type. Octopamine at 1 mu M increased phagocytosis in cockroach hemocytes exposed to Staphylococcus aureus in vitro, and this effect was mimicked by IP3 (10 mu M). The octopamine-treated hemocytes were shown to increase IP3 production in the latter stage of phagocytosis. Adult cockroaches exposed to an LD(50) dose of S. aureus in conjunction with either 0.1 mM octopamine or the octopamine(1) agonist, clonidine, had higher survival rates compared to saline-treated cockroaches. Correspondingly, the octopamine(1) antagonist, chlorpromazine, partially blocked the octopamine-mediated increase in cockroach survival. (C) 1994 Wiley-Liss, Inc.