Characterisation of [H-3]MK-801 binding and its cooperative modulation by pig brain membranes

Cooperative modulation of [H-3]MK-801 binding to extensively washed pig cortical brain membranes in the presence of various concentrations of L-glutamate, glycine, spermine, CPP and DCKA was evaluated in association experiments. In saturation experiments [3H]MK-801 labelled a homogeneous population of binding sites with a K-d-value of 1.26 +/- 0.18 nmol l(-1) and a B-max-value of 2130 +/- 200 fmol/mg protein. The pharmacological profile of this site was further evaluated in competition experiments with known NMDA receptor channel blockers. In nonequilibrium binding experiments EC(50)-values of reference compounds acting at the L-glutamate, at the glycine, and at the polyamine site, were determined by increasing or decreasing [H-3]MK-801 binding. Ifenprodil reduced [H-3]MK-801 binding in a biphasic manner. All the data obtained are in agreement with results from [H-3]MK-801 binding to rodent as well as human brain membranes. This study therefore strongly suggests, that pig cortical membranes are a suitable alternative to rodent brain membranes, and an acceptable substitute for human brain membranes in [H-3]MK-801 binding experiments.