SUBUNIT-SPECIFIC BLOCK OF CLONED NMDA RECEPTORS BY ARGIOTOXIN636

Cloned NMDA receptor channels of the NR1-NR2A, NR1-NR2B and NR1-NR2C t ype show differences in argiotoxin636 block. Mutations of an asparagin e residue located at a homologous position in the TM2 region of all NM DA receptor subunits, which corresponds to the Q/R site of the AMPA re ceptors, alters the argiotoxin636-induced block. The results suggest t hat the toxin interacts at this amino acid position with the putative pore forming TM2 region of the NMDA receptor subunits. Sequence differ ences in the TM2 segment of NR2A and NR2C subunits are not responsible for the subtype-specific sensitivity to argiotoxin636 as revealed by site-directed mutagenesis.