The influence of detergents on cloned potassium channels expressed in Xenopus oocytes was investigated. Bath application of Triton X-100 caused a dose-dependent reduction of the peak current through the delayed rectifier channel rKv2.1 and a fast, time- and voltage-dependent, current inactivation. Onset of inactivation was observed at concentrations as low as 1 microM; at 100 microM inactivation proceeded with a time constant of about 50 ms at +50 mV. The effect of Triton did not compete with extracellular TEA and the tail current kinetics was accelerated, indicating that the molecular mechanism is not a simple open-channel block. In patch-clamp recordings the effects were readily reversible and application of detergents from the inside were most effective. Triton induced similar effects in hKv1.5 channels; for rKv1.1., d-eag, and Kir2.1 mainly a current reduction was observed. No effect of 100 microM Triton was found for the plant inward rectifier channel KAT1. Investigation of Shaker channel mutants revealed a dependence of the Triton effect upon the degree and nature of C-type inactivation. Only detergents with a long hydrophobic carbohydrate chain and a hydrophilic chain of the polyethyleneglycol type caused inactivation of rKv2.1 (e.g., Triton X-100, Thesit, Brij35 were active; CHAPS and MEGA-8 wre inactive). The presented data reveal that there are channel- and detergent-specific interactions which can result in fast inactivation leading to physiological effects similar to those exerted by local anesthetics and antiarrhythmic agents.