title: cGMP/cGMP-dependent protein kinase pathway modulates nicotine-induced currents through the activation of α-bungarotoxin-insensitive nicotinic acetylcholine receptors from insect neurosecretory cells.
abstract: Insect neurosecretory cells, called dorsal unpaired median neurons, are known to express two α-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 μM guanosine triphosphate-γ-S increased nicotine currents through nAChR2. We also demonstrated that inhibition of PKG activity with 0.2 μM (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 (Ca(2+) ) activity because inhibition of Ca(2+) concentration with cadmium chloride (CdCl2 ) abolished KT5823-induced inhibition mediated by nAChR2. However, specific inhibition of nitric oxide-guanylyl cyclase (GC) complex by 10 μM 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 α-bungarotoxin-insensitive nAChR1 and nAChR2 are coupled to the cGMP/PKG pathway. We propose that nicotinic acetylcholine receptor activation induces an increase in intracellular calcium (Ca(2+) ) concentration. Elevation of intracellular Ca(2+) results in the formation of Ca(2+) -calmodulin (CaM) complex, which activates guanylyl cyclase (GC) and/or adenylyl cyclase (AC). Ca(2+) -CaM complex could activate Ca(2+) calmodulin kinase II which could directly or indirectly modulate the nicotinic response. The mechanisms by which cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) interact remain unclear. We demonstrate that nicotine-induced currents are coupled to the cGMP/PKG pathway.
authors.affiliation: Université d'Orléans, Laboratoire de Biologie des Ligneux et des Grandes Cultures (LBLGC), UPRES EA, Rue de Chartres, Orléans, France.|Université de Tunis El Manar, Faculté des Sciences, Campus Universitaire Farhat Hached, Rommana Tunis, Tunisie.
authors.forename: Safa
authors.initials: S
authors.lastname: Mannai
authors.affiliation: Université de Tunis El Manar, Faculté des Sciences, Campus Universitaire Farhat Hached, Rommana Tunis, Tunisie.
authors.forename: Lofti
authors.initials: L
authors.lastname: Bitri
authors.affiliation: Université d'Orléans, Laboratoire de Biologie des Ligneux et des Grandes Cultures (LBLGC), UPRES EA, Rue de Chartres, Orléans, France.
authors.forename: Steeve H
authors.initials: SH
authors.lastname: Thany
mesh_terms: D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology*; D019256:Cadmium Chloride / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D018678:Cholinergic Agents / Q000494:pharmacology; D003058:Cockroaches; D006152:Cyclic GMP / Q000378:metabolism* / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D009538:Nicotine / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011978:Receptors, Nicotinic / Q000378:metabolism
chemical_list: D002038:Bungarotoxins; D018678:Cholinergic Agents; D004791:Enzyme Inhibitors; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D009538:Nicotine; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D019256:Cadmium Chloride; D002118:Calcium
keywords: PKG; cGMP; guanylyl cyclase; nicotinic receptors