K[sup +] Occupancy of the N-methyl-D-aspartate Receptor Channel Probed by Mg[sup 2+] Block.

Investigates the potassium (K)-binding sites in the permeation pathway of rat recombinant NR1/NR2B NMDA receptor channels through the use of single-channel kinetics of extracellular magnesium (Mg) block. Effects of intracellular K on the apparent rates of Mg dissociation and permeation; Equilibrium dissociation constant and rate constants for Mg dissociation and permeation; Qualitative assessment of the affinity and selectivity of the internal site.