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

Abstract

SUMMARY1. Kinetic states and modes of a large-conductance Ca2+-activated K+ channel in excised patches of membrane from cultured rat skeletal muscle were studied with the patch clamp technique. Up to 106 open and shut intervals were analysed from each of seven different excised membrane patches containing a single channel.2. Plots of the mean durations of consecutive groups of ten to fifty open and shut intervals were made to assess kinetic stability of the channel. Occasional abrupt decreases in the mean open interval duration from normal to different distinct levels, which were maintained for hundreds to thousands of consecutive intervals, indicated entry of the channel into different modes. 5. During normal activity the distributions of interval durations were typically described by the sum of three to four exponential components for the open intervals and six to eight exponential components for the shut intervals, and this was the case for data obtained over a wide range of open channel probability resulting from different CaF+. These observations suggest that the channel can enter at least three to four open and six to eight shut states during normal activity.6. The numbers of detected states for data sets of different sample sizes drawn from normal activity agreed with theoretical predictions, and were essentially independent of the segment of normal activity from which the data sets were drawn. These observations are consistent with relative stability of channel kinetics during normal activity. Detection of each additional open or shut state after the first was found to require a 3-to 10-fold increase in the number of analysed events.

Multiple modes of N-type calcium channel activity distinguished by differences in gating kinetics

“…We referred to this as the "buzz mode," by analogy to a very rare pattern of activity of Ca2+-activated K+ channels (McManus and Magleby, 1988). The p, is -0.4, in the same range as the usual medium-p, gating, although the closed times are much shorter.…”

Linking Exponential Components to Kinetic States in Markov Models for Single-Channel Gating

“…In spite of the central importance of exponential components to the description of single channel data, little is known about the specifi c contributions of the various states to each of the exponential components. The question is not whether components can be calculated for a given kinetic scheme, as this is readily accomplished through analytical and Q-matrix methods (Colquhoun and Whereas it is relatively easy to detect slow exponential components of very small areas because of the high likelihood penalties that result if intervals of longer duration are not included in an exponential component ( McManus and Magleby, 1988 ), it is much more diffi cult to detect fast exponential components of small area superimposed on slower components. For example, when t C2 is fi vefold less than t C1 in Scheme 2, E 1 has a time constant of 0.18 ms and area of 0.01 ( Fig.…”

Emergence of ion channel modal gating from independent subunit kinetics

“…BK channels in rat skeletal muscle have been found to exhibit four modes when held at constant voltage and Ca 2+ concentration (13). Moving from the higher to lower open probability modes is associated with a restriction of a common state space and, in particular, a sequential removal of the longest-lived open states.…”

“…Several consistent possibilities have been suggested to explain modal gating in other channels, such as phosphorylation (16,17), binding of accessory proteins (13-15, 17, 20, 22, 24), ligand-independent conformational changes (13,19), or alterations at the channel pore (18). Our model demonstrates that, in general, these mechanisms can act locally, by influencing even a single subunit, and that this is sufficient to generate the many distinct channel states assumed in wholechannel models.…”

“…A detailed understanding of this important feature of IP 3 R behavior is therefore crucial for unraveling the complexity of Ca 2+ signaling and its role in cell function and disease. Modal gating has been observed in the kinetics of many other ion channels, such as K + (13)(14)(15)(16)(17)(18), Cl − (19), glutamate receptors (20,21), plasma membrane Ca 2+ (22)(23)(24), and ryanodine receptor Ca 2+ (25,26). However, the underlying biophysical basis of modal gating in the IP 3 R and most other channels remains unknown.…”