Figure 3.

τ_b and k_−,app depend on [Na⁺]_o. (a) Single-channel currents activated by 5 μM NMDA + 10 μM glycine during block by 30 μM Mg_o²⁺ at −90 mV with [Cs⁺]_i = 130 mM and the indicated [Na⁺]_o. In each pair of current traces, the section of the upper single-channel record indicated by the horizontal bar is replotted below the bar at higher time resolution. (b) Closed-time histograms corresponding to the currents shown in a to the left of each histogram. Lines are four-exponential fits to the histograms. Number of events in each histogram is more than 1,000. (c) Voltage dependence of k_−,app in three different [Cs⁺]_i. Symbol meanings are as in legend to Fig. 1 c and d. (d) Voltage dependence of k_−,app in three different [Na⁺]_o. Because k_−,app does not depend on [Cs⁺]_i (c), points are averages of data at a single [Na⁺]_o and one or more [Cs⁺]_i. ⋄, 140 mM Na_o⁺; ■, 105 mM Na_o⁺; ⧫, 70 mM Na_o⁺. Lines are drawn by using Eq. 3, with parameter values given in Table 1.