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Spermidine enhancement of [3H]MK-801 binding to the NMDA receptor complex in human cortical membranes
J E Steele1, D M Bowen, P T Francis
1Department of Neurochemistry, Institute of Neurology, London, U.K.
Abstract:
The effects of spermidine on the binding of [3H]MK-801 to the N-methyl-D-aspartate (NMDA) receptor complex was studied in human cerebral cortical membranes. [3H]MK-801 binding was increased from 56 +/- 5 fmol/mg protein (mean +/- S.E.M., n = 7) to 319 +/- 71 fmol/mg protein in the presence of 200 microM spermidine. The ED50 for spermidine stimulation of [3H]MK-801 binding was 89 +/- 22 microM (mean +/- S.E.M., n = 6). In the presence of glutamate (1 microM) plus glycine (1 microM) the ED50 was reduced to 5.5 +/- 0.7 microM. The increase in binding in the presence of spermidine was characterised by an increase in the rate of association of [3H]MK-801. In the presence of spermidine. [3H]MK-801 was inhibited by AP5. 7-chlorokynurenic acid and ifenprodil with IC50 values of 0.5 +/- 0.3 24 +/- 19 and 91 +/- 28 microM, respectively. None of these antagonists was a competitive inhibitor of the spermidine stimulation of [3H]MK-801 binding. Thus spermidine modulates the NMDA receptor complex in human brain, providing further evidence that the complex is similar in rat and human cortex.
Insights
Spermidine significantly enhances the binding of [3H]MK-801 to the N-methyl-D-aspartate (NMDA) receptor complex in human brain membranes. This modulation suggests similarities between human and rat NMDA receptor complexes.
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- The N-methyl-D-aspartate (NMDA) receptor complex is crucial for synaptic plasticity and cognitive functions.
- Understanding modulators of the NMDA receptor complex is vital for developing treatments for neurological disorders.
Purpose of the Study:
- To investigate the effects of spermidine on the binding of [3H]MK-801 to the NMDA receptor complex in human cerebral cortical membranes.
- To characterize the mechanism by which spermidine modulates NMDA receptor activity.
Main Methods:
- Radioligand binding assays using [3H]MK-801 in human cerebral cortical membranes.
- Determination of ED50 and IC50 values for spermidine and NMDA receptor antagonists.
- Analysis of the kinetics of [3H]MK-801 association in the presence of spermidine.
Main Results:
- Spermidine significantly increased [3H]MK-801 binding to the NMDA receptor complex in a dose-dependent manner.
- The ED50 for spermidine stimulation was reduced in the presence of glutamate and glycine.
- Spermidine increased the rate of [3H]MK-801 association, and its effects were not competitively inhibited by known NMDA receptor antagonists.
Conclusions:
- Spermidine acts as a positive modulator of the NMDA receptor complex in the human brain.
- The findings provide further evidence for the structural and functional similarity of NMDA receptor complexes in human and rat cortex.
- Spermidine's modulation of the NMDA receptor complex may have implications for neurological function and disease.