title: Does cyclic 3' ,5'-adenosine monophosphate act as second messenger in a voltage-dependent response to 5-hydroxytryptamine in Aplysia?
abstract: 1 The possibility that cyclic adenosine 3',5'-monophosphate (cyclic AMP) mediates a voltage-dependent inward current elicited by 5-hydroxytryptamine (5-HT) in RB and LB cells of the abdominal ganglion of Aplysia was tested. 2 Intracellular injection of cyclic AMP elicited an inward current with a similar time course, potential dependence and ionic sensitivity as the response to 5-HT. 3 Intracellular injection of guanylyl imidodiphosphate (GMP-PNP), which activated adenylate cyclase, neither mimicked nor enhanced the 5-HT-evoked current. On the contrary, it reduced the current. 4 The phosphodiesterase inhibitors, Ro20-1724, isobutyl methylxanthine (IBMX) and theophylline, each antagonized the voltage-dependent response to 5-HT. To varying degrees they each induced an inward current. 5 The adenylate cyclase antagonist, dithiobisnitrobenzoic acic (DTNB), had no effect on the response to 5-HT when applied either intracellularly or extracellularly. Intracellular injection of the phosphodiesterase activator imidazole also had no effect. 6 Tubocurarine and neostigmine did not reduce the voltage-dependent inward current evoked by 5-HT; methysergide elicited an inward current. 7 Although the observations that cyclic AMP and 5-HT can evoke similar voltage-dependent inward currents in RB and LB neurones of Aplysia might suggest a second messenger role for the cyclic nucleotide, the pharmacological data are inconsistent with this hypothesis.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001048:Aplysia / Q000187:drug effects / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007093:Imidazoles / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009388:Neostigmine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*; D013806:Theophylline / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D007093:Imidazoles; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D012701:Serotonin; D009388:Neostigmine; C029899:imidazole; D004228:Dithionitrobenzoic Acid; D013806:Theophylline; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine; D014403:Tubocurarine