The specific binding of the NMDA receptor (NR) channel ligand [(3)H]MK-801 to rat brain membranes is sensitive to positively charged buffer ingredients as to tris(hydroxymethyl)aminomethane (Tris), to Na(+), or to protons. Here we demonstrate that 16 non-competitive NR antagonists, including 5 long-chain diamines, classical NR channel blockers and several less known compounds, differ widely in their sensitivities to cationic buffer constituents. Although chemically distinguished either as extended di-cationic or as compact mono-cationic, their sensitivities to cationic buffer ingredients did not suggest this grouping. While the di-cationic compounds are known for their sensitivity to spermine (polyamine inverse agonists), also some of the mono-cationic blockers exhibited this feature. They might share as common target a recently described negatively charged extracellular GluN1/GluN2B interface.