title: Nitric oxide induces airway smooth muscle cell relaxation by decreasing the frequency of agonist-induced Ca2+ oscillations.
abstract: Nitric oxide (NO) induces airway smooth muscle cell (SMC) relaxation, but the underlying mechanism is not well understood. Consequently, we investigated the effects of NO on airway SMC contraction, Ca(2+) signaling, and Ca(2+) sensitivity in mouse lung slices with phase-contrast and confocal microscopy. Airways that were contracted in response to the agonist 5-hydroxytryptamine (5-HT) transiently relaxed in response to the NO donor, NOC-5. This NO-induced relaxation was enhanced by zaprinast or vardenafil, two selective inhibitors of cGMP-specific phosphodiesterase-5, but blocked by ODQ, an inhibitor of soluble guanylyl cyclase, and by Rp-8-pCPT-cGMPS, an inhibitor of protein kinase G (PKG). Simultaneous measurements of airway caliber and SMC [Ca(2+)](i) revealed that airway contraction induced by 5-HT correlated with the occurrence of Ca(2+) oscillations in the airway SMCs. Airway relaxation induced by NOC-5 was accompanied by a decrease in the frequency of these Ca(2+) oscillations. The cGMP analogues and selective PKG activators 8Br-cGMP and 8pCPT-cGMP also induced airway relaxation and decreased the frequency of the Ca(2+) oscillations. NOC-5 inhibited the increase of [Ca(2+)](i) and contraction induced by the photolytic release of inositol 1,4,5-trisphosphate (IP(3)) in airway SMCs. The effect of NO on the Ca(2+) sensitivity of the airway SMCs was examined in lung slices permeabilized to Ca(2+) by treatment with caffeine and ryanodine. Neither NOC-5 nor 8pCPT-cGMP induced relaxation in agonist-contracted Ca(2+)-permeabilized airways. Consequently, we conclude that NO, acting via the cGMP-PKG pathway, induced airway SMC relaxation by predominately inhibiting the release of Ca(2+) via the IP(3) receptor to decrease the frequency of agonist-induced Ca(2+) oscillations.
authors.affiliation: Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
authors.forename: Jose F
authors.initials: JF
authors.lastname: Perez-Zoghbi
authors.forename: Yan
authors.initials: Y
authors.lastname: Bai
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sanderson
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D066298:In Vitro Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000502:physiology*; D015290:Second Messenger Systems / Q000502:physiology; D014132:Trachea / Q000187:drug effects / Q000378:metabolism
chemical_list: D053496:Inositol 1,4,5-Trisphosphate Receptors; D009569:Nitric Oxide; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP