PMC

A, dorsal part of a 250 μm thick spinal cord slice. The SG is seen as a translucent band. B, IR-DIC image of a SG neurone in another thin slice. C, the neurone in B filled with Lucifer Yellow (0.1 %) via a whole-cell patch pipette.

Single-channel currents were activated in an outside-out patch upon bath-application of NMDA (60 μM) and glycine (3 μM). A, clusters of single-channel currents showing low- and high-conductance channel openings. V_h, -80 mV. B, direct transitions between open states of single-channel currents. V_h, -70 mV. C, cursor-fitted amplitude histogram of single-channel currents at -70 mV. The distribution was fitted with the sum of three Gaussian components. D, slope conductances for the three open levels estimated by the weighted least-squares fit (bars indicate s.d.). Reversal potential, -11.8 mV. E, patterns of open-open transitions. V_h, -70 mV. Vertical axis indicates the frequency of direct transitions between two consecutive conductance levels (ith opening followed by the (i+ 1)th opening, where i is an integer).

A-C, high-conductance single-channel currents activated by NMDA (50 μM) and glycine (10 μM) in an outside-out patch. B, cursor-fitted amplitude histogram at -70 mV. The histogram was fitted with the sum of two Gaussian components. Chord conductances were 58 pS (main state, 88 %) and 46 pS. Reversal potential, -11.7 mV. C, open-open transitions at -70 mV. D and E, block of high-conductance channels by ifenprodil (10 μM) in another high-conductance channel patch. D, currents were activated by glutamate (10 μM, glycine 10 μM). V_h, -70 mV. E, stability plot of charge transfer through channels plotted every 1 s. Left, control (mean, -2407 fC s⁻¹). Right, in the presence of ifenprodil (mean, -236 fC s⁻¹). Stability was confirmed by Spearman's rank order correlation test (5 % confidence limit).

A, pharmacological isolation of NMDA-EPSCs evoked by dorsal root stimulation at 0.1 Hz in nominally Mg²⁺-free solution containing 10 μM glycine, 20 μM bicuculline and 1 μM strychnine. Each superimposed trace is the average of five to seven records obtained at -50 mV or +50 mV (indicated). CNQX, 10 μM; AP-5, 50 μM. B, ifenprodil had no effect on NMDA-EPSCs recorded from another neurone at -50 mV. Averaged EPSCs before and 7 min after application of 10 μM ifenprodil are superimposed. Stimulation at 0.1 Hz. C, the decay phase of NMDA-EPSCs at +50 mV was fitted by a double exponential function (superimposed curve). Dashed lines indicate the two components. Average of three EPSCs evoked at 0.05 Hz. D, current-voltage relations of NMDA-EPSCs recorded from another neurone in the presence of 1 mM Mg²⁺. The Boltzmann fit (see Methods) indicates an inward current peak at -40.5 mV. K_d at 0 mV, 1.9 mM. As shown in sample records (averaged EPSCs at indicated V_h), the decay of pharmacologically isolated NMDA-EPSCs became faster at more hyperpolarized negative V_h values. E, Mg²⁺ sensitivity of NMDA-EPSCs. The Boltzmann fit to normalized conductances (6 cells) gave K_d of 3.6 mM at 0 mV, 160 μM at -60 mV, and 57 μM at -80 mV. Open circle is G_max and bars represent s.e.m.