Fig. 2.

Glycine concentration–response curves from 27- to 29-d-old cortical neurons reveal a low-affinity glycine component.A, Representative glycine concentration–response data from a typical neuron. Inward currents were elicited in response to 2 sec fast applications of 100 μm NMDA at 29 sec intervals (intervening sections of the trace have been omitted for clarity) in the presence of increasing concentrations of glycine. Applied glycine concentrations are shown. The baseline glycine contamination was calculated as 6 nm. Therefore, the true glycine concentration was calculated as the applied glycine concentration plus 6 nm. B, Plot of the glycine concentration-peak current response data from A. Shown is a biphasic curve fitted with the 2 × 2 equivalent binding site model (solid line) that yieldedmK_D values and relative amplitudes of 16 nm (30%) and 520 nm (70%) for the high- and low-affinity components, respectively. A monophasic curve fitted with the two-equivalent site model (broken line) is shown for comparative purposes. C, Plot of the glycine concentration–response data from eight neurons. Data from each neuron have been normalized to their respective individual 30 μmglycine peak response. Shown is a biphasic curve fitted with the 2 × 2 equivalent binding site model (solid line) that yielded mK_D values and relative amplitudes of 41 nm (52%) and 774 nm (48%) for the high- and low-affinity components, respectively. The biphasic fit was significantly better than a monophasic fit using the two-equivalent biding site model (broken line) (p < 0.001, F test).D, Comparison of glycine concentration–response data from 2- to 3-d-old rats (open circles) and 27- to 29-d old rats (closed circles). Data from each neuron have been normalized to their respective individual 1 μmglycine peak response.