The gating of single calcium-dependent potassium channels is described by an activation/blockade mechanism

Abstract

Single calcium dependent potassium channels from cultured rat myoballs have been studied with the patch clamp technique, and current records subjected to statistical analysis. From the dependence of the mean open state probability on the internal calcium concentration, two calcium ions are required to open the channel. The open state and closed state lifetime distributions reveal that the usual activation model is not applicable to these channels. They are consistent with a two step gating mechanism that involves both activation by calcium and blockade by a calcium-sensitive gate.

Kinetic states and modes of single large‐conductance calcium‐activated potassium channels in cultured rat skeletal muscle.

“…This conclusion is consistent with previous data which suggests that this channel can open with either one, two, three or more calcium ions bound (Barrett et al 1982;Methfessel & Boheim, 1982;Magleby & Pallotta, 1983a, b;Vergara & Latorre, 1983;Golowasch, Kirkwood & Miller, 1986) (Cox & Miller, 1965;Colquhoun & Hawkes, 1981). A discrete Markov model, rather than a continuum model, has also been found to give a better description of the distribution of open times from an acetylcholine receptor channel (Horn, 1987).…”

“…At present, then, it seems most productive to consider the kinetics of the largeconductance Ca2+-activated K+ channel as being described by a Markov process with discrete states (Methfessel & Boheim, 1982;Magleby & Pallotta, 1983a, b; Moczydlowski , as such a model can give rise to sums of exponential components which are consistent with the observed data. However, it should be kept in mind that such models are probably only an approximation, as conformational changes in other studied proteins can differ from simple Markov processes (Ansari, Berendzen, Bowne, Frauenfelder, Iben, Sauke, Shyamsunder & Young, 1985).…”

“…Previous studies of the large-conductance Ca21-activated K+ channel have suggested a minimum of two or three open states and three or more shut states (Barrett et al 1982;Methfessel & Boheim, 1982;Magleby & Pallotta, 1983 a;Moczydlowski & Latorre, 1983;Pallotta, 1985 a, b). The ability to identify different kinetic modes (Figs 1-5), improvements in time resolution, maximum-likelihood fitting which weighs each interval based on its probability of occurrence (Colquhoun & Sigworth, 1983), and efficient data handling techniques which allow 105-106 intervals to be analysed as easily as several hundred (McManus et al 1987) have greatly increased the ability to distinguish kinetic states.…”

“…The large conductance of this channel allows single-channel currents to be recorded with high time resolution, and consequently considerable progress has been made towards understanding the molecular gating mechanism of this channel. Previous studies have suggested a minimum of two to three open states of similar conductance and three or more shut states (Barrett et al 1982;Methfessel & Boheim, 1982; Magleby & Pallotta, 1983 a, b;Moczydlowski & Latorre, 1983;Pallotta, 1985 a, b).…”

Charybdotoxin block of single Ca2+-activated K+ channels. Effects of channel gating, voltage, and ionic strength.

“…identifying characteristics include high K + selectivity, high single-channel conductance, activation by both cytoplasmic Ca 2+ and depolarizing voltages, and allosteric modulation of Ca 2 § action by cytoplasmic Mg 2+ (Many, 1981;Barrett et al, 1982;Methfessel and Boheim, 1982;Moczydlowski and Latorre, 1983;Magleby and Pallotta, 1983;Petersen and Maruyama, 1984;Blatz and Magleby, 1984;Yellen, 1984;Eisenman et al, 1986;Golowasch et al, 1986; Oberhauser, A., O. Alvarez, and R. Latorre, manuscript submitted for publication). Recently, a high-affinity inhibitor directed against this channel was discovered in the venom of the scorpion Leiurus quinquestriatus (Miller et al, 1985), from which it was subsequently purified (Smith et al, 1986).…”