Cooperative Modulation of [³H]MK‐801 Binding to the N‐Methyl‐d‐Aspartate Receptor‐Ion Channel Complex by l‐Glutamate, Glycine, and Polyamines

Abstract

In extensively washed rat cortical membranes [3H](+)-5-methyl-10,11-dihydro-5 H-dibenzo [a,d]cyclohepten-5,10-imine ([3H]MK-801) labeled a homogeneous set of sites (Bmax = 1.86 pmol/mg protein) with relatively low affinity (KD = 45 nM). L-Glutamate, glycine, and spermidine produced concentration-dependent increases in specific [3H]MK-801 binding due to a reduction in the KD of the radioligand. In the presence of high concentrations of L-glutamate, glycine, or spermidine, the KD values for [3H]MK-801 were reduced to 11 nM, 18 nM, and 15 nM, respectively. Maximally effective concentrations of combinations of the three compounds further increased [3H]MK-801 binding affinity as follows: L-glutamate + glycine, KD = 6.2 nM; L-glutamate + spermidine, KD = 2.2 nM; glycine + spermidine, KD = 8.3 nM. High concentrations of spermidine did not inhibit either [3H]glycine orf [3H]3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding to the N-methyl-D-aspartate (NMDA) receptor complex. The concentration of L-glutamate required to produce half-maximal enhancement (EC50) of [3H]MK-801 binding was reduced from 218 nM to 52 nM in the presence of 30 microM glycine and to 41 nM in the presence of 50 microM spermidine. The EC50 value for glycine enhancement of [3H]MK-801 binding was 184 nM. This was lowered to 47 nM in the presence of L-glutamate and to 59 nM in the presence of spermidine. Spermidine enhanced [3H]MK-801 binding with an EC50 value of 19.4 microM which was significantly reduced by high concentrations of L-glutamate (EC50 = 3.9 microM) or glycine (EC50 = 6.2 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

A Review of Glutamate Receptors I: Current Understanding of Their Biology

“…Zn ++ blocks the channel in a voltage-independent manner 3 2 0 , whereas the polyamine site 3 2 1 , 3 2 2 binds compounds such as spermine or spermidine, either potentiating 321,322 or inhibiting 322 the activity of the receptor. Potentiation or inhibition depends on the combination of subunits forming each NMDA receptor 322 .…”

Crystal Structure and Pharmacological Characterization of a Novel N-Methyl-d-aspartate (NMDA) Receptor Antagonist at the GluN1 Glycine Binding Site

“…Brain membranes were prepared according to the method described by Ransom and Stec (28). TK40 was dissolved as a 1 mM stock solution in 50% DMSO-water.…”

Blockade of AMPA Receptors Reduces Brain Edema following Opening of the Blood—Brain Barrier

“…It has been shown that some polyamines (e.g. , spermine and spermidine) can alter the activ ity of NMDA receptors (Ransom and Stec, 1988) and protamine may have a similar effect. The lack TABLE 2.…”