σ^{2} estimates of single channel properties for channels with two conductance levels. In A, predicted σ^{2}/*I* relationships for a population of 1,000 channels in which each channel can occupy a main conductance level (*i*_{1}) of 20 units and a second level, *i*_{2}, as indicated. Fractional occupancy in each level is 0.5. In each case, a parabolic relationship is expected, but the maximal possible value of *I* when all channels are open depends on the relative amplitudes of *i*_{1} and *i*_{2}. The curve in red approximates the expectation based on the single channel properties of Slo3. In B, the values of *i* (solid circles) and *P*_{o} (diamonds) based on applying to the parabolas in A are given for different values of *i*_{2}. For estimates of *i*, the estimated value is given as a percentage of the nominal value of *i*_{1}, while, for *P*_{o}, the value given is the percentage by which the apparent *P*_{o} defined from application of will underestimate the true *P*_{o}. For comparison, the weighted-mean estimate of single channel current based on the relative amplitudes and fractional occupancy in each of two open states based on amplitude histograms is given (open circles). For the case applicable to Slo3 (red symbols), *i* estimated using will be within 10% of the weighted-mean estimate of average single channel current, while the *P*_{o} estimate will underestimate the true *P*_{o} by ∼10%. In C, the impact of changing the relative occupancy, *k*, in *i*_{2} and *i*_{1} is considered, while in D, the impact of *k* on parameter estimates using are shown.

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