Effects of certain diuretics on the electrophysiological characteristics of the nephron in the rat kidney.

Electrophysiological micropuncture techniques were used to study the effect of certain diuretics on transtubular transport of electrolytes in the rat kidney. The mercurial diuretic novurite caused a reduction of active sodium transport in the proximal tubule, measured by short-circuit current and increased permeability of the tubular wall to ions which led to a considerable drop in transtubular potential and transepithelial resistance. Ethacrynic acid decreased the short-circuit current in the proximal tubule, without changing the permeability characteristics of the nephron. Xanthine diuretic euphylline did not reduce the short-circuit current in the proximal segment of the nephron; however, it increased the transepithelial potential of the renal tubule. In the distal tubule, euphylline and ethacrynic acid increased the difference in transtubular potential, whereas novurite reduced the transtubular potential. An increase in the electrical gradient of the distal tubule as a result of euphylline and ethacrynic acid action may be responsible for increasing potassium excretion. A decrease of the transtubular potential in the potassium excretion under mercurial diuretic action. The reduction of tubular reabsorption as a result of diuretic action is due to drug effect on different levels of the transtubular-ion transport system.