BENZYL-POLYAMINES - NOVEL, POTENT N-METHYL-D-ASPARTATE RECEPTOR ANTAGONISTS

The effects of benzyl-polyamines were studied at recombinant N-methyl- D-aspartate (NMDA) receptors expressed in Xenopus laevis oocytes. A nu mber of mono-, di- and tri-benzyl polyamines, having benzyl substituti ons on the terminal or central amino groups, inhibited responses of NR 1/NR2 receptors in oocytes voltage-clamped at -70 mV. Among the most p otent compounds was N-1,N-4,N-8-tri-benzyl-spermidine (TB-3-4), which had an IC50 value of 0.2 mu M. TB-3-4 was similar to 40-fold more pote nt at NR1/NR2A and NR1/NR2B receptors than at NR1/ NR2C or NR1/NR2D re ceptors. Block by TB-3-4 was strongly voltage dependent. Using voltage ramps analyzed by the Woodhull model of voltage-dependent channel blo ck, TB-3-4 was found to have a K-d(0) value of 5 mu M and a z delta va lue of 1.41 at NR1/NR2B channels, whereas the affinity of binding [K-d (0) = 250 mu M] but not the degree of voltage-dependence (z delta = 1. 43) was much lower at NR1/NR2D channels. At a concentration of 10 mu M , TB-3-4 had no effect on lpha-amino-3-hydroxy-5-methyl-4-isoxazolepro pionic acid receptors expressed from the GluR1 subunit, indicating tha t TB-3-4 is a selective NMDA antagonist. TB-3-4 did not permeate wild- type NMDA channels but could easily permeate channels containing an N6 16G mutation in the NR1 subunit. This mutation is presumed to increase the size of the narrowest constriction of the NMDA channel, thus allo wing passage of TB-3-4. Benzyl-polyamines such as TB-3-4 represent a s tructurally novel class of NMDA receptor channel blockers.