Figure 3. Effect of Mg²⁺_o on open-duration histograms of NR1/2D receptors.

A, single-channel recordings of NR1/2D receptor-mediated currents at −85 mV are shown in the presence of the indicated [Mg²⁺]_o at a slower (upper trace of each pair) and faster (lower traces) time base. B, open-duration histograms at −85 mV from the same patch as used for A in the presence of the indicated [Mg²⁺]_o. Each histogram was fitted with three components except for in 50 μm Mg²⁺_o, which was fitted with two components. In each [Mg²⁺]_o, the time constant (and relative amplitude) of each component of the fits was: 0 Mg²⁺_o, 96 μs (28%), 0.54 ms (64%), 1.4 ms (9%); 10 μm Mg²⁺_o, 48 μs (28%), 0.48 ms (71%), 0.82 ms (1%); 30 μm Mg²⁺_o, 147 μs (22%), 0.30 ms (76%), 1.1 ms (1%); 50 μm Mg²⁺_o, 78 μs (31%), 0.24 ms (69%). C, the apparent blocking rate constant for Mg²⁺_o, k_+,app, was estimated from the slope of a linear regression line fitted to a plot of 1/τ_oversus[Mg²⁺]_o.