[25] Investigating single-channel gating mechanisms through Analysis of two-dimensional dwell-time distributions

The use of single-channel recording techniques and the application of stochastic theory have led to great advances in our understanding of ion channel gating mechanisms. The gating of many types of ion channels can be described as a “Markov process,” containing a discrete number of open and closed states, with the rate constants for transitions among the states remaining constant in time for constant conditions. This chapter discusses additional uses and interpretations of 2-D kinetic analysis of single-channel data. It first summarizes the theory underlying 2-D analysis and present methods for the display of 2-D data and interpretation of dependencies. It then presents a method for quantifying irreversible transitions in single-channel gating using the 2-D distributions. Finally, it addresses the limitations of 2-D analysis by giving examples of the way the interpretation of component dependencies may lead to incorrect assumptions about the connections between states. Despite its limitations, 2-D analysis can provide a useful means to extract kinetic information from single-channel data and to test channel gating mechanisms.