The stimulation of Na+ uptake in frog skin by uranyl ions.
1. 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.
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001001:Anura; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D010539:Permeability; D010710:Phosphates / Q000378:metabolism; D011893:Rana esculenta; D012867:Skin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014501:Uranium / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D010710:Phosphates; D014501:Uranium; D000584:Amiloride; D012964:Sodium