Studies Concerning the Action of Trivalent Cations on the Mechanical Reponse of Guinea-pig Ureter

1. Effects of various trivalent cations on the mechanical response of smooth muscle of guinea-pig ureter were examined. 2. Responses were inhibited by trivalent cations in low concentrations. The order of inhibition was La , Y > Ho, Sm. 3. Potentiation in tension development due to TEA and Ba was depressed by used these cations. Sr did not increase the response in normal solution but it was recovered by the addition of Sr in Ca-free solution. The recovery by Sr also inhibited by used cations. 4. The inhibition of response was observed in Mn solution. Effect of Mn on the mechanical response was stronger than La . 5. In Ca-free solution, recovery due to the addition of Ba was also inhibited by trivalent cations having the order of La > Ho . La failed the Ba -induced recovery. 6. Potassium contracture was depended on the external calcium concentration. Lineweaver-Bulk plot on relationship between Ca concentration and potassium contracture in trivalent cations and Mn indicated linear. These results indicate the competitive action to the same calcium store. 7. The action of trivalent cations to super ficial calcium sites, bound calcium and Ca movement for contraction was discussed.