TABLE III.
Fit Parameters for Apparent Open Time and Blocking Frequency Plots
| Membrane potential | |||
|---|---|---|---|
| −70 | −110 | −150 | |
| mV | mV | mV | |
| Apparent open time plot | |||
| k T+1 (μM−1 s−1) | 95 ± 2 | 100 ± 3 | 114 ± 5 |
| Intercept (s−1) | 1,195 ± 86 | 1,744 ± 101 | 1,456 ± 112 |
| Blocking frequency plot | |||
| k T +1 (μM−1 s−1) | 69 ± 1 | 70 ± 4 | 83 ± 5 |
| Intercept (s−1) | 37 ± 47 | 97 ± 143 | 76 ± 138 |
Fit parameters are from linear regression to the data in Fig. 5, B and C, and are given ± SE (errors derived from linear regression). According to Scheme B1, the slope of either plot should give an estimate of the association rate for tacrine (k T+1). At each membrane potential, comparison of the slopes (Zar, 1984) revealed that the two plot methods yield significantly different values of k T+1 (P < 0.0005).