Properties of single potassium channels in vesicles formed from the sarcolemma of frog skeletal muscle.

The patch-clamp method was used to study unitary delayed rectifier K+ channels in large vesicles formed from the membrane of frog skeletal muscle. Channels were activated by depolarizing pulses. Single-channel conductance was about 15 pS in physiological [K+]o and was doubled by raising [K+]o to 120 mM. TEA+ caused an apparent reduction in single-channel current, which we attribute to a rapid block. When depolarizations were repeated at brief intervals, records with and without channel openings were ordered non-randomly, providing evidence for a slow process which was probably inactivation. In multichannel patches the relation between variance and mean current, binomial analysis, and the distribution of times for single and double openings were all consistent with channels behaving independently. Open times were distributed exponentially. Mean open time, tau o, increased with depolarization so that 1/tau o was an exponential function of voltage. First latency histograms peaked at times later than zero and could not be fitted by a scheme having only two closed states. Channel openings occurred in bursts and closed time histograms could be fitted by the sum of three exponentials. Our results imply a scheme with at least three closed states, an open and an inactivated state.