Inhibition of autoradiographic MK-801 binding by an endogenous factor

In an autoradiographic assay of glutamate/glycine-stimulated [3H]MK-801-binding, a 30-min prewash of tissue sections in buffer resulted in a 40-78% enhancement of binding over that in the absence of a prewash. Inclusion of buffer used for the prewash in the binding assay significantly inhibited binding in prewashed sections. Addition of competitive glutamate and glycine antagonists to the prewash buffer significantly reduced the effect of a prewash except in striatum. The presence of EDTA in the binding assay of unwashed sections did not alter binding, suggesting the prewash effect is not mediated by divalent cations. The results suggest the presence of a differentially distributed endogenous substance that inhibits MK-801-binding.