RETURNYonago Acta medica 1991;34:65-82
Effects of Magnesium Ions on Tracheal Smooth Muscle Contraction in Guinea Pigs
Mitsunobu Yamamoto, Yuji Kawasaki and Yutaka Hitsuda
Third Department of Internal Medicine, Faculty of Medicine, Tottori University, Yonago 683, Japan
The effects of Mg ions on inhibiting and relaxing the tracheal chain contraction induced by histamine, acetylcholine or KCl were investigated in guinea pigs. In 1.8 mM Ca-containing Tyrode's solution, Mg inhibited the maximum phasic contraction induced by histamine or KCl in a dose-dependent manner. However, this inhibitory effect was not observed on the acetylcholine-induced contraction. In Ca-free Tyrode’s solution, Mg also inhibited the maximum phasic contraction induced by histamine, dose-dependently. The histamine-induced contraction in the presence of Ca in Tyrode's solution consisted of 2 components, a fast phasic and a slow phasic contraction. The fast phasic contraction was inhibited by Mg in an obviously dose-dependent manner. All tonic contractions induced by these 3 agonists were relaxed by MgCl2 administration, dose-dependently. The relaxing activities of Mg were decreased in the following order: KCl-, histamine- and acetylcholine-induced contractions. These results suggest that Mg ions have inhibitory and relaxing effects on the airway smooth muscle contraction, and that these effects are related to the action in which Mg ions block Ca influx into the cytoplasm from the extracellular space and Ca release from the intracellular Ca depots.
Key words: acetylcholine; airway smooth muscle; bronchial asthma; histamine; Mg ion