Fig. 2.

Synaptically released glutamate displaces kainate and desensitizes AMPA receptors. A, eEPSCs at a holding potential of −17 mV in control conditions, superimposed on a steady-state kainate current, and after recovery. Each traceis the mean of two to four responses with no leak subtraction.B, The same responses, filtered at 1 kHz and with the steady-state currents subtracted, show a net positive current attributable to a block of the kainate current during the falling phase of the synaptic current. The continuous curve superimposed on the 0.5 mm kainate response is a single exponential with a time constant of 66 msec. C, The relation between the unblocked current and the magnitude of the peak control synaptic conductance in the presence of a low or high kainate concentration. The percentage of kainate current remaining was determined after baseline subtraction, as in B, by subtracting the record in control. The peak positive current then was divided by the steady-state kainate current to yield fractional blocked kainate current. The percentage of remaining current = 100 × (1 − fractional blocked current). The line is a linear regression; r = −0.7. Dotted linesin A and B show the zero current level.