5‐Hydroxytryptamine‐sensitive adenylate cyclase affects phagocytosis in cockroach hemocytes

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Abstract
The effects of 5‐hydroxytryptamine (5‐HT), octopamine, and dopamine on adenylate cyclase activity were studied using fragmented hemocyte membranes of the American cockroach, Periplaneta americana. 5‐HT and octopamine increased cAMP production with maximal effects at 10 nM and 10 μM respectively. Dopamine did not affect adenylate cyclase activity. The effects of octopamine and 5‐HT are not additive, indicating that both are working through the same receptor. A pharmacological profile suggests that the receptor present on the cockroach hemocytes is more similar to a 5‐HT receptor than an octopamine receptor. Mammalian antagonists of 5‐HT‐receptors blocked the 5‐HT‐induced increase in cAMP production with the following order of potency: mianserin > ketanserin > spiperone > ICS 205,930. In phagocytosis assays using whole hemocytes, 5‐HT increases cAMP production above control levels at 0.25, 0.75, 15, and 65 min. Addition of Bt2cAMP at 0.1 mM inhibits phagocytosis whereas, at 10 nM, Bt2cAMP enhances phagocytosis. Imidazole at 0.1 mM also enhanced phagocytosis. A 5‐HT‐mediated elevation in cAMP production may result in either an activation or inhibition of phagocytic activities.

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