title: Nitric oxide increases excitability by depressing a calcium activated potassium current in snail neurons.
abstract: In gastropods, the interneuronal messenger, nitric oxide (NO), modulates spike frequency and synaptic transmission. We have characterized the effect of NO on ion currents underlying neuronal excitability, using current-clamp and two-electrode voltage-clamp techniques. Identified neurons of the pulmonate snail, Helix pomatia, respond to the NO donor sodium nitroprusside (SNP) by increasing the firing frequency and decreasing the latency. Voltage-clamp experiments revealed that SNP or S-nitro-N-acetylpenicillamine (SNAP) depressed the macroscopic outward current, while the control compound N-acetylpenicillamine (NAP) had no effect. Current voltage curves generated from voltage steps to different membrane potentials ranging from -40 to +180 mV showed an N-shaped outward current. Superfusion of ganglia with Ca(2+) free Helix solution abolished the N-shape, indicating the contribution of a Ca(2+) activated K(+) current (I(K,Ca)). Exposure of neurons to SNP or SNAP diminished the N-shape, indicating that NO affects I(K,Ca). The depressing effect of SNP on the outward current was slow and reached steady state in about 5 min. In conclusion, our findings indicate that NO enhances excitability in Helix nervous system by decreasing I(K,Ca).
authors.affiliation: Department of Molecular Neurobiology and Cellular Physiology, Institute of Zoology, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Zsombok
authors.forename: S
authors.initials: S
authors.lastname: Schrofner
authors.forename: A
authors.initials: A
authors.lastname: Hermann
authors.forename: H H
authors.initials: HH
authors.lastname: Kerschbaum
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002490:Central Nervous System / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006372:Helix, Snails / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D026423:S-Nitroso-N-Acetylpenicillamine
chemical_list: D015220:Calcium Channels; D020030:Nitric Oxide Donors; D015221:Potassium Channels; D009599:Nitroprusside; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D010396:Penicillamine; D002118:Calcium