AN ENDOGENOUS LIGAND FOR THE KAINATE-TYPE BINDING-SITES FROM RAT-BRAIN

Extracts from the rat brain were screened to identify a putative endog enous ligand for the binding sites of the neuroexcitant kainic acid (K A). The extracted substances were separated by chromatographic techniq ues and tested for their ability to inhibit KA binding to fish synapto somes and to membranes from rat brain. A substance isolated in this wa y (rat kainate-binding inhibitor, RKBI) displays a competitive interac tion with KA for the low-affinity binding sites in rat brain membranes . According to the separation behavior in the purification step, RKBI is distinct from an inhibitor formerly isolated from fish nervous tiss ue (KBI). The substance exhibits positive co-operativity with KA for a very-low-affinity site population, particularly concentrated in the c erebellum, and could play a physiological role in this area.