Journal of Neuroscience, Vol 9, 2191-2196, Copyright © 1989 by Society for Neuroscience
HA-966 antagonizes N-methyl-D-aspartate receptors through a selective interaction with the glycine modulatory site
AC Foster and JA Kemp
Merck Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Harlow, Essex, England.
3-Amino-1-hydroxypyrrolid-2-one (HA-966) has been known for several years
as an excitatory amino acid antagonist, acting principally at the
N-methyl-D-aspartate (NMDA) receptor subtype. We report here that HA- 966
blocks NMDA responses through a selective interaction with the glycine
modulatory site present within the receptor complex. In radioligand binding
experiments, HA-966 inhibited strychnine- insensitive 3H-glycine binding to
rat cerebral cortex synaptic plasma membranes with an IC50 of 17.5 microM.
At concentrations up to 1 mM, HA- 966 caused minimal inhibition of
radioligand binding to the transmitter recognition sites of the NMDA,
quisqualate, or kainate receptor subtypes and was similarly inactive
against the binding of 3H- strychnine to rat spinal cord/brain stem
membranes. In electrophysiological experiments, HA-966 produced a selective
block of NMDA responses in a rat cortical slice preparation. The degree of
antagonism caused by HA-966 was maximal at 250 microM and was not increased
further by raising the HA-966 concentration. Both glycine (1 mM) and
D-serine (100 microM) reversed the antagonism of NMDA responses caused by
HA-966. In patch-clamp experiments using rat cortical neurons in culture,
HA-966 blocked the potentiation of NMDA responses by glycine but had little
effect on basal NMDA responses themselves. This profile of antagonism
differs from that observed with 7- chlorokynurenate, another recently
discovered antagonist of the glycine site on the NMDA receptor (Kemp et
al., 1988) and may indicate that glycine antagonists of differing
efficacies can exist. Previous experiments with HA-966 may now be
interpreted to suggest that activation of the glycine site on the NMDA
receptor occurs in vivo and is important for the participation of NMDA
receptors in synaptic transmission.