title: Sodium nitroprusside stimulates Ca2+ -activated K+ channels in porcine tracheal smooth muscle cells.
abstract: To directly investigate the possible role of large-conductance Ca2+ -activated K+ (KCa) channels in nitro-vasodilator-induced relaxation of airway smooth muscle, we used cell-attached patch-clamp techniques to test the effects of sodium nitroprusside (SNP) on KCa channels in freshly dispersed porcine tracheal smooth muscle cells. Channel open-state probability (nPo) increased approximately 13-fold with exposure to 10(-5) M SNP, and this was partially reversed by addition of the guanylate cyclase inhibitors methylene blue (3 X 10(-4) M) or LY-83583 (5 X 10(-5) M). Pretreatment with the guanosine 3',5' -cyclic monophosphate (cGMP)-dependent protein kinase (G kinase) inhibitor Rp-8-(p-chlorophenylthio) cGMP-phosphorothioate (2 X 10(-5) M) prevented activation of KCa channels by SNP. We also tested the ability of G kinase to directly activate KCa channels in inside-out patches. G kinase (2.5 U/microliter) with ATP (0.5 mM) and cGMP (0.1 mM), but not ATP and cGMP alone, increased nPo approximately 23-fold. We conclude that SNP activates KCa channels in airway smooth muscle via guanylate cyclase and G kinase. Phosphorylation of the channel protein by G kinase may account for this response. Consequent membrane hyperpolarization and inhibition of Ca2+ entry through voltage-dependent channels may contribute to SNP-induced relaxation of airway smooth muscle.
authors.affiliation: Department of Anesthesiology, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205, USA.
authors.forename: M
authors.initials: M
authors.lastname: Yamakage
authors.forename: C A
authors.initials: CA
authors.lastname: Hirshman
authors.forename: T L
authors.initials: TL
authors.lastname: Croxton
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008751:Methylene Blue / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009599:Nitroprusside / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012044:Regression Analysis; D013552:Swine; D013873:Thionucleotides / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects / Q000502:physiology*
chemical_list: C090860:8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphorothioate; D000634:Aminoquinolines; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D013873:Thionucleotides; D009599:Nitroprusside; D000255:Adenosine Triphosphate; C041715:6-anilino-5,8-quinolinedione; D017869:Cyclic GMP-Dependent Protein Kinases; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D002118:Calcium; D008751:Methylene Blue