Na+/K+ ATPase mediates rhythmic spontaneous relaxations in canine airway smooth muscle.
In canine airway smooth muscle, cyclopiazonic acid (CPA; selective blocker of the sarcoplasmic reticulum Ca(2+)-pump) evokes a contractile response which is initially mediated via release of internally sequestered Ca2+, but is later supported almost exclusively by electromechanical coupling. As such, this second component is highly sensitive to inhibition of voltage-dependent Ca(2+)-influx (e.g. dihydropyridines, removal of external Ca2+) or to membrane hyperpolarization. In the present study, we describe relaxations which occur spontaneously during this second component of the CPA-evoked contraction. These relaxations are also electromechanically mediated, since they are abolished by depolarization of the membrane by high-K+ media. TEA has relatively little effect on the phasic activity, thus ruling out an involvement of Ca(2+)-dependent K+ channels. On the other hand, the phasic activity is abolished by ouabain, by removal of external K+, or by cooling and is markedly slowed by removal of external Na+. These observations indicate that the phasic activity is mediated by the Na+/K(+)-ATPase.
Janssen
L J
LJ
Department of Medicine, McMaster University, Hamilton, Ontario, Canada. janssenl@fhs.csu.mcmaster.ca
Nana
R
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D000818:Animals; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D007211:Indoles / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D012132:Respiratory Muscles / Q000187:drug effects*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology*
D007211:Indoles; D014665:Vasodilator Agents; D000254:Sodium-Potassium-Exchanging ATPase; C000543:cyclopiazonic acid