Differential Regulation of Ionotropic Glutamate Receptors

¹ Western Washington University
² University of Richmond

^* To whom correspondence should be addressed. E-mail: gentile{at}chem.wwu.edu.

Submitted on May 24, 2006
Revised on July 14, 2006
Accepted on 31 October 2006

	Abstract

Ionotropic glutamate receptors (iGluRs), a family of ligand gated ion channels, are responsible for the majority of fast excitatory neurotransmission in the CNS. Within this family, different members serve distinct roles at glutamatergic synapses. AMPA (amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors mediate fast depolarization while NMDA (N-methyl-D-aspartate) receptors mediate the slower component of the excitatory postsynaptic potential. These disparate functions suggest alternate modes of regulation. In this work we show that endogeneous regulators of iGluRs have different abilities to bind to specific domains of NMDA NR1-1b and AMPA GluR2 subunits. We have previously shown that the sulfated neurosteroids pregnenolone sulfate (PS) and 3-hydroxy-5-pregnan-20-one sulfate (PregaS) bind to the extracellular glutamate binding core (S1S2) of the GluR2 subunit. Here we show that neither neurosteroid binds to the S1S2 domain of the NMDA NR1-1b sununit. This NR1-1b NMDA domain does, however, bind to the endogeneous polyamines spermine and spermidine as well as Zn(II). Binding of the polyamines and Zn(II) to the S1S2 domain of the GluR2 subunit was not observed. This binding of Zn(II) and polyamines to the S1S2 domain of the NR1-1b subunit defines a new binding site for each of these modulators.

Key Words: AMPA, NMDA, iGluR, neurosteroids, polyamines

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