Effect of furosemide on the thermodynamic parameters of frog skin.

The formalism of nonequilibrium thermodynamics (NET) was used to analyze the effect of diuretic furosemide on the transport mechanism of frog skin. Mucosal furosemide increased the active conductance of Na+ across the mucosal membrane of the cells, producing an increased transport of Na+ (short-circuit current). Furosemide also increased both the thermodynamic affinity of the metabolic reaction supplying energy to the sodium pump and the degree of coupling between transport and metabolism. It changed the phenomenological cross-coefficient of the NET description as well as the stoichiometric ratio, indicating that its effect cannot be explained simply on the basis of a change in Na+ conductance. The effect on the NET parameters was independent of the presence of either chloride or sulfate as the principal anion in the solutions, and was qualitatively similar to the effect produced by mucosal application of triphenylmethylphosphonium ion.