Table 1

Characterization of glutamate-evoked current responses mediated by NR1/NR2A and NR1/NR2B

NMDA receptor subunit combinationτDSτDFτDφ[Ca2+]eVrevNa+/K+VrevCa2+/K+VrevCa2+/K+ + Zn2+
msec msec msec mV mV mV
NR1/NR2A651  ± 41 (32)148  ± 18 (32)770  ± 87 (6)5.3  ± 0.8 (57)37  ± 3 (3)37  ± 2 (3)
NR1/NR2B715  ± 71 (20)N.D.5.5  ± 1.1 (23)38  ± 2 (3)39  ± 3 (3)

All values represent mean ± standard error. The number of different cells used to calculate each value is given in parentheses. N.D., not done. Time constant for agonist-induced current was determined using pCLAMP software. Desensitization of NR1/NR2A currents was best fit to a biexponential curve, giving a fast (τDF) and a slow (τDS) decay, whereas that of NR1/NR2B currents was best fit to a single exponential decay. [CaCl2]e = 1.8 mm. Desensitization of NR1/NR2A currents was best fit by a single exponential curve in nominally Ca2+-free extracellular recording solution ([Ca2+]e). Current-voltage relationships were obtained as described in legend to Fig. 1B. To determine the Ca2+-versus-K+ reversal potential, the extracellular solution was replaced with solution containing high Ca2+ and no Na2+ (see text). The reversal potentials of the two receptor subtypes were not significantly different. The zinc concentration used was 1 μm for NR1/NR2A and 10 μm for NR1/NR2B.