Ionic mechanisms underlying electrical slow waves in canine airway smooth muscle

Am J Physiol. 1998 Sep;275(3):L516-23. doi: 10.1152/ajplung.1998.275.3.L516.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bronchi / drug effects
  • Bronchi / physiology*
  • Calcium Channels / physiology
  • Chloride Channels / physiology
  • Dogs
  • Evoked Potentials / drug effects
  • In Vitro Techniques
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology*
  • Muscle, Smooth / drug effects
  • Muscle, Smooth / physiology*
  • Niflumic Acid / pharmacology
  • Oscillometry
  • Ouabain / pharmacology
  • Potassium / pharmacology
  • Potassium Channels / physiology
  • Sodium-Potassium-Exchanging ATPase / metabolism
  • Tetraethylammonium / pharmacology
  • Time Factors


  • Calcium Channels
  • Chloride Channels
  • Potassium Channels
  • Niflumic Acid
  • Ouabain
  • Tetraethylammonium
  • Sodium-Potassium-Exchanging ATPase
  • Potassium