Relaxation of airway smooth muscle induced by potassium in the presence of Ca-antagonists.
We examined K+-induced relaxation instead of contraction in the presence of Ca-antagonists by measuring isometric tension in the tracheal smooth muscle isolated from guinea pigs. Cumulative administration of KCl (10-90 mM) induced a concentration-dependent contraction. When the muscle was pretreated with low concentrations of Ca-antagonists, cumulative administration of KCl caused a mild contraction, followed by a moderate relaxation. In the muscle pretreated with high concentrations of Ca-antagonists, KCl revealed a concentration-related relaxation without contraction. The potency ratios of Ca-antagonists to reverse the KCl-induced contraction to relaxation were nifedipine : verapamil : diltiazem = 94:4:1. This order of potency was quite similar to that of Ca-antagonists to relax the muscle precontracted with KCl (30 mM). Magnitudes of KCl (30 m,)-induced relaxation in the presence of Ca-antagonists were similar to those caused by Ca-antagonists in the KCl (30 mM)-precontracted muscles. Thus, K+-induced relaxation in the airway smooth muscle in the presence of Ca-antagonists may be due to the voltage-dependent increase in binding of Ca-antagonists to calcium channels.
Koga
Y
Y
Department of Anesthesiology, Tohoku University School of Medicine, Sendai, Japan.
Sodeyama
N
N
Satoh
S
S
Teshigawara
T
T
Yanagisawa
T
T
Taira
N
N
Endoh
M
M
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004110:Diltiazem / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D014132:Trachea / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D014700:Verapamil; D004110:Diltiazem; D009543:Nifedipine; D011188:Potassium