Kainate binding to the AMPA receptor in rat brain

Displacement of ³H]AMPA and ³H]CNQX by kainate was measured in membranes and solubilized fractions from rat brain. In soluble fractions, plots of ³H]AMPA and ³H]CNQX binding displaced by kainate resulted in one-site fits with K_i values in the range of 1–3 M. In membranes, plots of ³H]AMPA binding displaced by kainate resulted in graphs which were better fit by twosite regression analysis than by a one-site fit. The K_i value for the high-affinity component of these two-site fits was 3–9 M and the low-affinity component K_i was in the range of 70–120 M; similar values were determined for kainate displacement of ³H]CNQX. The presence of thiocyanate ions had no effect on kainate displacement of ³H]CNQX. Since the affinity for kainate of the presumed synaptic AMPA receptor is in the range of EC₅₀ values for kainate determined from physiological studies, these data contribute further evidence for the idea that kainate binding to synaptic AMPA receptors may be responsible for many of kainate's physiological effects.