cGMP/cGMP-dependent protein kinase pathway modulates nicotine-induced currents through the activation of alpha-bungarotoxin-insensitive nicotinic acetylcholine receptors from insect neurosecretory cells

摘要

Insect neurosecretory cells, called dorsal unpaired median neurons, are known to express two alpha-bungarotoxin-insensitive nicotinic acetylcholine receptor (nAChR) subtypes, nAChR1 and nAChR2. It was demonstrated that nAChR1 was sensitive to cAMP/cAMP-dependent protein kinase (PKA) regulation, resulting in a modulation of nicotine currents. In this study, we show that cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG) pathway modulates nicotine-induced currents, as increased cGMP affects the second compound of the biphasic current-voltage curve, corresponding to the nAChR2 receptors. Indeed, maintaining the guanosine triphosphate level with 100 mu M guanosine triphosphate-gamma-Sincreased nicotine currents through nAChR2. We also demonstrated that inhibition of PKG activity with 0.2 mu M (8R, 9S, 11S)(-)- 9-methoxy-carbamyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cycloocta-(c,d,e)-trinden-1-one (KT5823), a PKG specific inhibitor, reduced nicotine-induced current amplitudes. KT5823 effect on nicotine currents is associated with calcium (Ca2+) activity because inhibition of Ca2+ concentration with cadmium chloride (CdCl2) abolished KT5823-induced inhibition mediated by nAChR2. However, specific inhibition of nitric oxide-guanylyl cyclase (GC) complex by 10 mu M 1H-[1,2,4] oxadiazolo[ 4,3-a]quinoxalin-1-one (ODQ) significantly increased nicotine-induced current amplitudes on both nAChR1 and nAChR2. These results suggest that nicotine-induced currents mediated by both alpha-bungarotoxin-insensitive nAChR1 and nAChR2 are coupled to the cGMP/PKG pathway.