title: Ionic mechanisms underlying electrical slow waves in canine airway smooth muscle.
abstract: In canine bronchial smooth muscle (BSM), spasmogens evoke oscillations in membrane potential ("slow waves"). The depolarizing phase of the slow waves is mediated by voltage-dependent Ca2+ channels; we examined the roles played by Cl- and K+ currents and Na+-K+-ATPase activity in mediating the repolarizing phase. Slow waves were evoked using tetraethylammonium (25 mM) in the presence or absence of niflumic acid (100 microM; Cl- channel blocker) or ouabain (10 microM; block Na+-K+-ATPase) or after elevating external K+ concentration ([K+]) to 36 mM (to block K+ currents); curve fitting was performed to quantitate the rates of rise/fall and frequency under these conditions. Slow waves were markedly slowed, and eventually abolished, by niflumic acid but were unaffected by ouabain or high [K+]. Electrically evoked slow waves were also blocked in similar fashion by niflumic acid. We conclude that the repolarization phase is mediated by Ca2+-dependent Cl- currents. This information, together with our earlier finding that the depolarizing phase is due to voltage-dependent Ca2+ current, suggests that slow waves in canine BSM involve alternating opening and closing of Ca2+ and Cl- channels.
authors.affiliation: Asthma Research Group and Smooth Muscle Research Program, Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
authors.forename: L J
authors.initials: LJ
authors.lastname: Janssen
authors.forename: C
authors.initials: C
authors.lastname: Hague
authors.forename: R
authors.initials: R
authors.lastname: Nana
mesh_terms: D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D018118:Chloride Channels / Q000502:physiology; D004285:Dogs; D005071:Evoked Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009544:Niflumic Acid / Q000494:pharmacology; D009991:Oscillometry; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D018118:Chloride Channels; D015221:Potassium Channels; D009544:Niflumic Acid; D010042:Ouabain; D019789:Tetraethylammonium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium