Interference of Shot Noise of Open-Channel Current with Analysis of Fast Gating: Patchers do not (Yet) Have to Care |
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Authors: | Indra Schroeder Ulf-Peter Hansen |
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Institution: | (1) Department of Structural Biology, University of Kiel, Leibnizstr. 11, 24098 Kiel, Germany |
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Abstract: | Microsecond gating of ion channels can be evaluated by fitting beta distributions to amplitude histograms of measured time
series. The shape of these histograms is determined not only by the rate constants of the gating process (in relation to the
filter frequency) but also by baseline noise and shot noise, resulting from the stochastic nature of ion flow. Under normal
temporal resolution, the small shot noise can be ignored. This simplification may no longer be legitimate when rate constants
reach the range above 1 μs−1. Here, the influence of shot noise is studied by means of simulated time series for several values of single-channel current
of the fully open state and baseline noise. Under realistic optimal conditions (16 pA current, 1 pA noise, 50 kHz bandwidth),
ignoring the shot noise leads to an underestimation of the rate constants above 1 μs−1 by a factor of about 2.5. However, in that range, the scatter of the evaluated rate constants is at least of the same magnitude,
obscuring the systematic error. The incorporation of shot noise into the analysis will become more important when amplifiers
with significantly reduced noise become available. |
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Keywords: | Beta distribution Markov model Microsecond gating Poisson distribution Open-channel noise Rate constant |
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