Octopaminergic modulation of the single Ca2+ channel currents in Kenyon cells isolated from the mushroom body of the cricket brain

Octopamine plays an important role in mediating reward signals in olfactory learning and memory formation in insect. However, its target molecules and signaling pathways are still unknown. In this study, we investigated the effects of octopamine on the voltage-activated Ca2+ channels expressed in native Kenyon cells isolated from the mushroom body of the cricket(Gryllus bimaculatus) brain. The cell-attached patch clamp recordings with 100 niM Ba2+ outside showed the presence of dihydropyridine (DHP) sensitive L-type Ca2+ channels with a single channel conductance of approximately 21 +/- 2 pS (n = 12). The open probability (NPo) of single Ca2+ channel currents decreased by about 29 +/- 7% (n = 6) by bath application of 10 mu M octopamine. Octopamine-induced decrease in Po was imitated by bath application of 8-Br-cAMP, a membrane-permeable cAMP analog. Pre-treatment of Kenyon cells with the octoparnine receptor antagonist phentolamine blocked the inhibitory effect of octoparnine on Ca2+ channels. Pretreatment of Kenyon cells with H-89, a selective inhibitor of cAMP-dependent protein kinase (PKA) attenuated the inhibitory effect of bath applied octoparnine on Ca2+ channels. These results indicate that DHP-sensitive L-type Ca2+ channel is a target protein for octoparnine and its modulation is mediated via cAMP and PKA-dependent signaling pathways in freshly isolated Kenyon cell in the cricket G. bimaculatus. (C) 2008 Elsevier Ltd. All rights reserved.