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 octopamine₁-type. Octopamine at 1 μM increased phagocytosis in cockroach hemocytes exposed to Staphylococcus aureus in vitro, and this effect was mimicked by IP₃ (10 μM). The octopamine-treated hemocytes were shown to increase IP₃ production in the latter stage of phagocytosis. Adult cockroaches exposed to an LD₅₀ dose of S. aureus in conjunction with either 0.1 mM octopamine or the octopamine₁ agonist, clonidine, had higher survival rates compared to saline-treated cockroaches. Correspondingly, the octopamine₁ antagonist, chlorpromazine, partially blocked the octopamine-mediated increase in cockroach survival. © 1994 Wiley-Liss, Inc.