The Na+ uptake in the isolated from skin of Rana esculenta was measured by the short-circuit current (Isc). Uranyl ions increase at pH 5.5 the Isc up to 200% at concentrations of 10 mM. The half-maximal value for this effect is at about 1 mM uranyl salt. 2. The effect is (a) specific for the Na+-selective membrane, (b) fully reversible. No stimulation can be seen in presence of 1 mM H+ or 0.1 mM amiloride. 3. The decrease of the sodium permeability of the apical membrane (PNa), normally induced by increasing concentrations of Na+ in the mucosal solution, %Na]o, is partially prevented by uranyl ions. The apparent Michaelis constant of the saturable Na+ uptake is shifted to much higher values. 4. A comparison between the uranyl effect and similar effects of the other drugs leads to the conclusion that uranyl ions might act in a polar hydrophobic environment, possibly by combining with phosphate groups (of phospholipids), and, thus, enhancing Na+ permeability by changes in tertiary structure near each Na channel. The interaction of mucosal Na+ with their receptor, normally triggering the [Na]o-dependent decrease of PNa, is thought to be diminished by uranyl association in a neighbouring region, causing a noncompetitive stimulation of the Na+ translocation though the apical frog skin membrane.
摘要
用短路电流（Isc）测量食用蛙离体皮肤的Na⁺摄取量。在pH 5.5时，10 mM浓度的铀酰离子可使Isc增加高达200%。此效应的半数最大值约在1 mM铀盐浓度时出现。2. 该效应（a）对Na⁺选择性膜具有特异性，（b）完全可逆。在存在1 mM H⁺或0.1 mM氨氯吡咪时未见刺激作用。3. 黏膜溶液中Na⁺浓度（[Na]o）增加通常所诱导的顶端膜钠通透性（PNa）降低，可被铀酰离子部分阻止。可饱和Na⁺摄取的表观米氏常数移至更高值。4. 对铀酰效应与其他药物类似效应的比较得出结论，铀酰离子可能在极性疏水环境中起作用，可能是通过与（磷脂的）磷酸基团结合，从而通过每个Na⁺通道附近三级结构的变化增强Na⁺通透性。黏膜Na⁺与其受体的相互作用通常会触发依赖于[Na]o的PNa降低，而在邻近区域的铀酰结合被认为会减弱这种相互作用，从而导致通过顶端蛙皮肤膜的Na⁺转运受到非竞争性刺激。
