The present study was designed to elucidate the acute effects of mercury ions on electrogenic transport systems in rat proximal and distal convoluted tubules. Male Munich Wistar rats were anesthetized with Inactin and prepared for micropuncture in the usual way. Under control conditions, the transepithelial potential difference (PDte) approaches -3.2 +/- 0.6 mV in early proximal tubules, +2.1 +/- 0.3 mV in late proximal tubules, and -17.8 +/- 1.8 mV in distal convoluted tubules. PDte of neither early nor late proximal tubules was significantly affected by the acute application of mercury ions. In the distal tubules, mercury ions (10 mumol/l) lead to a gradual depolarization of the epithelium from -17.8 +/- 1.8 to -9.3 +/- 2.7 mV within 8 min. A linear correlation between PDte under control conditions and depolarization caused by amiloride is seen. The slope of this correlation is significantly reduced during the application of mercury ions. In conclusion, mercury ions decrease the distal PDte an effect possibly contributing to altered renal electrolyte excretion following the acute administration of mercury ions. The depolarization is, at least in part, due to an inhibition of amiloride-sensitive sodium channels at the luminal cell membrane of principal cells.