A comparative study on the contraction induced by high K+/Na+ deficient solution in rat uterus or urinary bladder

In the present paper, effects of high K+/Na+ deficient solution on the rat uterus were examined on the mechanical response, wet weight of the tissue or rate of oxygen consumption, and they were compared with those in rat urinary bladder. In the uterus, isosmotic substitution of K+ for Na+ in a physiological salt solution (PSS) induced a contraction followed by a small sustained contraction, while hyperosmotic addition of KCl to PSS induced a sustained contraction. The hyperosmotic KCl addition increased the rate of oxygen consumption in comparison with that in PSS, and the substituted high K+/Na+ deficient solution decreased it as compared with that in the hyperosmotic KCl addition. Similar results were shown in the urinary bladder. At 120 min after application of the substituted high K+/Na+ deficient solution, the relative wet weight increased in the uterus, but did not change in the urinary bladder. Both the decrease in the developed tension and the increase in the wet weight of the uterus were prevented by the hyperosmotic addition of sucrose. In the urinary bladder, the decreased tension was significantly prevented by the hyperosmotic addition of NaCl to the PSS or substitution of pyruvate or oxalacetate for glucose, whereas it was slightly prevented by the hyperosmotic addition of sucrose. From these results, it is suggested that the decrease of the developed tension in isosmotically substituted high K+/Na+ deficient solution in rat uterus is probably due to cell swelling and that the inhibition of contraction in urinary bladder is mainly caused by the inhibition of glucose utilization by Na+ deficiency in the medium.