Comparison of receptor occupancy obtained with different transmitter release models at two simulated temperatures
| Transmitter Release Model | Description of Transmitter Pulse | Temp.2-d (°C) | Receptor Occupancy | |
|---|---|---|---|---|
| 1 mM 1-ms pulse | Constant,2-a‘Square’ | 0.2 ms ramp-up +0.8 ms+0.2 ms ramp-down | 22 | 78% |
| 1 mM 1-ms pulse | Constant, ‘Square’ | 0.2 ms ramp-up +0.8 ms +0.2 ms ramp-down | 37 | 93% |
| Double-exp-decay pulse | High,2-bslow2-c | A1 = 2.7 mM; τ1 = 0.1 ms | 22 | 84% |
| A2 = 0.41 mM; τ2 = 2.1 ms | ||||
| Double-exp-decay pulse | High, slow | A1 = 2.7 mM; τ1 = 0.1 ms | 37 | 100% |
| A2 = 0.41 mM; τ2 = 2.1 ms | ||||
| Double-exp-decay pulse | High, fast2-c | A1 = 2.7 mM; τ1 = 0.025 ms | 22 | 46% |
| A2 = 0.41 mM; τ2 = 0.52 ms | ||||
| Double-exp-decay pulse | High, fast | A1 = 2.7 mM; τ1 = 0.025 ms | 37 | 90% |
| A1 = 0.41 mM; τ2 = 0.52 ms | ||||
| Double-exp-decay pulse | Low,2-bslow | A1 = 1.1 mM; τ1 = 0.1 ms | 22 | 66% |
| A2 = 0.17 mM; τ2 = 2.1 ms | ||||
| Double-exp-decay pulse | Low, slow | A1 = 1.1 mM; τ1 = 0.1 ms | 37 | 97% |
| A2 = 0.17 mM; τ2 = 0.025 ms | ||||
| Double-exp-decay pulse | Low, fast | A1 = 1.1 mM; τ1 = 0.025 ms | 22 | 16% |
| A2 = 0.17 mM; τ2 = 0.52 ms | ||||
| Double-exp-decay pulse | Low, fast | A1 = 1.1 mM; τ1 = 0.025 ms | 37 | 63% |
| A2 = 0.17 mM; τ2 = 0.52 ms |
The Q10 of NMDARs was set at 2.5 based on previous work (McLarnon and Curry, 1990). The time course of the 'square' pulse with a linear ramp-up and down was set according to the limitations of our perfusion system. The time course and amplitudes for the first two double exponential decay pulses were set as described in Clements (1996). The time course and amplitudes for the last six double exponential decay pulses were adjusted to examine the effect of altered transmitter peak amplitude and faster glutamate clearance. Receptor occupancy was calculated from the ratio of the peak current obtained under the conditions described below to the maximal current obtained (saturating dose, long application). The NMDAR model used below is based on the NR1A/NR2A parameters from Table 1.
↵2-a Glutamate concentration stays constant for 0.8 ms after 0.2-ms ramp-up.
↵2-b High indicates that the initial peak glutamate concentration is high (2.7 mM + 0.41 mM), whereas low indicates that the initial peak glutamate concentration is low (1.1 mM + 0.17 mM); the 2.7 mM peak and 0.41 mM tail are from the revised estimates of synaptic cleft glutamate concentration made byClements (1996); the 1.1 mM peak glutamate concentration is from the original estimate of synaptic cleft glutamate concentration made byClements et al. (1992).
↵2-c Slow indicates that glutamate concentration decays with slower time constants (0.1 ms and 2.1 ms), whereas fast indicates that glutamate concentration decays with faster time constants (0.025 ms and 0.52 ms);
↵2-d Temperature at which parameters were determined.