Dual signalling by different octopamine receptors converges on adenylate cyclase in Sf9 cells

The Sf9 insect cell line, derived from Spodoptera frugiperda, was used to study the regulation of adenylate cyclase (AC) activity by octopamine receptors. The cyclic AMP (CAMP) production was stimulated in a concentration-dependent manner by octopamine. Octopamine also elicited a rise in cytosolic Ca2+. The Ca2+ elevation was independent of the cAMP elevation whereas the cAMP elevation was partially inhibited by removal of Call. The antagonistic effects of a series of compounds were tested on both responses. Phentolamine inhibited both responses with similar potency. Two of the tested compounds, MK-912 and RS 79948, were over 1000-fold more potent in blocking the Ca2+ response. Ionomycin, a Ca2+ ionophore, or activation of the heterologously expressed muscarinic M-3 receptors in the cells did not alone stimulate cAMP production. However, a Ca2+ elevation potentiated cAMP production in the presence of a primary stimulant such as forskolin or activated G(s) proteins. This type of regulation of AC is different from previously identified Ca2+-sensitive AC isoforms. For comparison the Ca2+/calmodulin-activated type I AC was expressed and demonstrated to be stimulated directly by an increase in Ca2+. Together the results demonstrate that octopamine can synergistically regulate the AC activity via two different receptors in Sf9 cells. (C) 2002 Elsevier Science Ltd. All rights reserved.