title: Nitric oxide decreases a calcium-activated potassium current via activation of phosphodiesterase 2 in Helix U-cells.
abstract: In the present study, we investigated the underlaying mechanism of nitric oxide (NO) and cGMP on the decline of a Ca2+-activated potassium (KCa) current in U-cells of the right parietal ganglion of the pulmonate snail, Helix pomatia. Using a two-electrode voltage-clamp technique, we activated a KCa-current either by opening of endogenous voltage-gated Ca2+-channels during depolarizing voltage steps or by ionophoretic injection of Ca2+ via a third electrode containing 100 mM Ca2+. KCa-current amplitude in U-cells was sensitive to Ba2+, TEA, iberiotoxin, kaliotoxin and charybdotoxin (ChTX), but not to 4-aminopyridine (4-AP) (up to 30 mM) and apamin (up to 300 nM). Thus, the biophysical and pharmacological profile of the KCa-current in U-cells shares similarities with the large-conductance KCa channel (BKCa). The NO-donor sodium nitroprusside (SNP) or S-nitro-N-acetylpenicillamine (SNAP) as well as NO-gas decreased the KCa-current amplitude and decreased the rate of KCa-current activation elicited by Ca2+-injection. Decline of the current amplitude and decrease of activation of KCa-current were qualitatively mimicked by the membrane-permeable cGMP analogue dibutyryl-cGMP (db-cGMP). NO-induced decrease of KCa-current was blocked by methylene blue (50 microM), an inhibitor of the guanylyl-cyclase, and by erytho-9-(2-hydroxyl-3-nonyl) adenine (EHNA) (100 microM), an inhibitor of the cGMP-stimulated phosphodiesterase 2 (PDE2). These experiments suggest that the NO-mediated decrease of KCa-current in U-cells results from synthesis of cGMP by activation of a guanylyl-cyclase and subsequent activation of PDE2.
authors.affiliation: Department of Molecular Neurobiology and Cellular Physiology, Institute of Zoology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Schrofner
authors.forename: Andrea
authors.initials: A
authors.lastname: Zsombok
authors.forename: Anton
authors.initials: A
authors.lastname: Hermann
authors.forename: Hubert H
authors.initials: HH
authors.lastname: Kerschbaum
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D006152:Cyclic GMP / Q000096:biosynthesis; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D006162:Guanylate Cyclase / Q000187:drug effects / Q000378:metabolism; D006372:Helix, Snails / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009420:Nervous System / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D009474:Neurons / Q000187:drug effects / Q000201:enzymology; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009924:Organ Culture Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D020030:Nitric Oxide Donors; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D009569:Nitric Oxide; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D002118:Calcium