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Kamizaki, J., Shimizu, K., Nakajyo, S. and Urakawa, N. A change in inhibitory mechanism of Na+deficiency on high K+-induced contraction in rat uterus with the progress of pregnancy. Jpn. J. Smooth Muscle Res.In the present paper, effects of high K+/Na+deficient solution on the rat uterus with the progress of the pregnancy were examined on the mechanical response and wet weight. The progress of pregnancy was divided in four stages, early stage (Day 4 and 5 of pregnancy), middle stage (Day 8-10), late stage (Day 14 and 15) and end stage (Day 21). In the early stage muscle, an isosmotically substituted high K+/Na+ deficient (iso-154K+) solution induced a large contraction followed by a decrease in tension level, though a hyperosmotic KCl addition induced a large sustained contraction. Similar results were shown in muscles of the middle and late stages, However, a maximum tension level and a subsequent inhibition by the iso-154K+ solution in the end stage muscle were smaller than those of other stages. On the other hand, iso-154K+solution remarkably increased the relative cellular water content in the early or middle stage muscle, but moderately in the late or end stage one. In the muscle of all stages, a hyperosmotic addition of sucrose reversed the inhibition of muscle tension and the cell swelling by the iso-154K+ solution. Moreover, a substitution of more impermeable anion (C2H5COO-) for Cl-in the iso-154K+solution decreased the inhibition of the contraction in the early stage muscle, but increased it in the end stage one. Thesubstitution for Cl-with more permeable anion (NO3-or I-) produced a greater inhibition of contraction in all stage muscles. Moreover, a substitution of pyruvate or oxalacetate forglucose in iso-154K+solution did not affect the decreased tension in the early stage muscle, however, reversed the decreased tension in those after the middle stage. From these results, the decrease of the developed tension in the iso-154K+solution in the early stage muscle is probably due to cell swelling and those after the middle stages is probably caused by both the cell swelling and the inhibition of glucose utilization by Na+deficiency in the medium. The data suggest that the mechanism of the decrease in tension is probably transferred from cell swelling to inhibition of glucose utilization with the progress of pregnancy.

Ueda, F., Kishimoto, T., Karaki, H. and Urakawa, N. High K-induced Contraction in Rabbit and Monkey Tracheal Smooth Muscle. Jap.J. Smooth Muscle Res., 1983, 19 (6), 541-549. - High K-induced contractions in rabbit and monkey tracheal smooth muscle were characterized. A substituted 60mM K, 94.1mM 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 60mM 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 154.1mMK, Na deficient solution induced a rapid rise in tension followed by a gradual decrease. Wet weight of rabbit trachea increased in the 154.1mM K solution. Both the decrease in the developed tension and the increase in the wet weight were prevented by the hyperosmotic addition of sucrose (50-100mM). The decrease in the developed tenison was also partially antagonized by the addition of pyruvate or oxalacetate. In monkey trachea, the sustained contraction induced by the 154.1mM 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, N a 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.