Effects of D(2)O and Osmotic Gradients on Potential and Resistance of the Isolated Frog Skin

Exposure of the outside surface of isolated frog skin (R. pipiens and R. catesbeiana) to sulfate solution made up with D(2)O decreased skin potential and resistance. Exposure of the inside surface to D(2)O solution decreased the potential slightly but increased the resistance. The changes were linearly related to the D(2)O concentration. Since D(2)O acts like a hyperosmotic solution, the skin potential and resistance were studied upon exposure to solution made hyperosmotic by addition of sucrose, mannitol, acetamide, urea, thiourea, Na(2)SO(4), or K(2)SO(4). Skin potential and resistance decreased when the outside solution was made hyperosmotic. The changes depended upon the concentration and the nature of the solute. Thiourea and urea solutions were the most effective. Treatment of the inside surface gave relatively small decreases in potential; the resistance either increased or remained unchanged. These effects appeared to depend upon the direction of the osmotic gradient across the skin rather than upon the value of the osmolarity compared to normal body fluids. Experiments with a series of six polyhydric alcohols from methanol to mannitol and the polysaccharides, sucrose and raffinose, showed adonitol with 5 carbons to decrease the potential the most. Smaller and larger compounds of this set gave lesser effects. As yet no consistent explanation of the effects is forthcoming, but their demonstration calls for caution in the indiscriminate use of solutes such as mannitol or sucrose "to make up the osmolality" and in the neglect of urea because "it penetrates freely."