Radioligand kinetics at the NMDA receptor channel revisited: An active part by Na+ and Tris

Abstract

[ 3 H]MK-801 is widely used as a marker for NMDA receptors (NRs), indicating the opening frequency of the associated ion channel. Association and dissociation of this radioligand in membranes prepared from rat cerebral cortex were accelerated by Na + ions (EC 50 70 mM, n H 3). The widely used primary amine buffer tris(hydroxymethyl) aminomethane (Tris) had similar influences, but not the tertiary amine buffer bis(2-hydroxyethyl) amino-tris(hydroxymethyl)methane (BisTris). These results are in agreement with previous physiological data suggesting a site for Na + ions increasing the opening frequency of the NR.