The action of external tetraethylammonium ions on unitary delayed rectifier potassium channels of frog skeletal muscle.

1. We have used single-channel recording to investigate the block by extracellular tetraethylammonium ions (TEA+) of delayed rectifier potassium channels of frog skeletal sarcolemma. 2. TEA+ blocks by reducing the apparent amplitude of unitary currents, without detectable increase in open-level current variance. 3. The block by TEA+ appeared to be 1:1, the fractional current being halved at 5.8 mM and -3 mV. The dissociation constant for the block was voltage dependent, increasing e-fold for a 138 mV depolarization. 4. Activation of delayed rectifier potassium currents is not altered by TEA+. 5. Open times, which in the presence of TEA+ represents bursts of open and blocked events, are not increased by TEA+, indicating that blocked channels are able to close normally.