The influence of different extracellular chloride concentrations of chloride channel blockers and of inorganic anions on renal basolateral organic cation transport was examined on isolated nonperfused S2 segments of superficial proximal tubules of rabbit kidney. Tritium-labeled tetraethylammonium (TEA) with a high specific activity of 13.5 Ci/mmol was used as a model substrate of the organic cation transport system. With the experimental conditions chosen, the TEA accumulation in the cells reflects the TEA transport across the basolateral membrane. A maximum TEA cell to a bath ratio of 711 was observed at a TEA bath concentration of 1.4 x 10(-7) M. Increasing TEA bath concentrations lead to a nonlinear reduction of the TEA cell to the bath ratio. Superficial proximal S2 segments showed a significantly higher accumulation of TEA as compared to the S1 or S3 segments. No significant differences could be found between superficial and juxtamedullary S2 segments. Chloride ions significantly modulated the basolateral cation transport system in the S2 segments. In a chloride-free medium, virtually no TEA transport could be detected. Furthermore, iso-osmotic replacement of chloride in the incubation medium by iodide, sulfate or nitrate significantly reduced tubular TEA accumulation, whereas bromide was without effect. Chloride channel blockers had no effect on TEA transport, and TEA did not significantly influence 36chloride uptake of the S2 segments. Our study demonstrates extensive concentrative TEA accumulation in S2 proximal segments at the low TEA bath concentrations. Extracellular chloride may modulate the tubular TEA uptake, probably indirectly via the basolateral chloride/bicarbonate exchanger. A chloride/TEA cotransport seems to be excluded.