KAINATE BINDING TO THE AMPA RECEPTOR IN RAT-BRAIN

Displacement of [H-3]AMPA and [H-3]CNQX by kainate was measured in membranes and solubilized fractions from rat brain. In soluble fractions, plots of [H-3]AMPA and [H-3]CNQX binding displaced by kainate resulted in one-site fits with K-i values in the range of 1-3 mu M. In membranes, plots of [H-3]AMPA binding displaced by kainate resulted in graphs which were better fit by two-site 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 mu M and the low-affinity component K-i was in the range of 70-120 mu M; similar values were determined for kainate displacement of [H-3]CNQX. The presence of thiocyanate ions had no effect on kainate displacement of [H-3]CNQX. Since the affinity for kainate of the presumed synaptic AMPA receptor is in the range of EC(50) 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.