High K-induced contractions in rabbit and monkey tracheal smooth muscle

High K-induced contractions in rabbit and monkey tracheal smooth muscle were characterized. A substituted 60 mM K, 94.1 mM Na solution produced a sustained contraction in both preparations. The 60 mM K-induced contraction in rabbit trachea was inhibited by Ca removal, verapamil, glucose-removal and hypoxia but not by sodium nitroprusside. The 60 mM K-induced contraction in monkey trachea was inhibited by Ca removal, verapamil, sodium nitroprusside and hypoxia but not by glucose-removal. In rabbit trachea a substituted 154.1 mM K, Na deficient solution induced a rapid rise in tension followed by a gradual decrease. Wet weight of rabbit trachea increased in the 154.1 mM K solution. Both the decrease in the developed tension and the increase in the wet weight were prevented by the hyperosmotic addition of sucrose (50-100 mM). The decrease in the developed tension was also partially antagonized by the addition of pyruvate or oxalacetate. In monkey trachea, the sustained contraction induced by the 154.1 mM K solution showed very slow decrease following the increase in the wet weight of the tissue. The decrease in muscle tension was prevented by the addition of hyperosmotic sucrose. These results suggest that, in rabbit tracheal smooth muscle, the decrease in the developed tension in isosmotically substituted high K, Na deficient solution may be attributable mainly to the swelling of muscle cells and partly to the inhibition of glucose utilization resulting from Na deficiency. In contrast, the contraction in monkey trachea seems to be inhibited, although slightly, by the swelling of the cells.