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The Journal of Neurophysiology Vol. 83 No. 5 May 2000, pp. 2844-2853
Copyright ©2000 by the American Physiological Society
Department of Physiology and Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203
Chuang, Shih-Chieh,
Riccardo Bianchi, and
Robert K. S. Wong.
Group I mGluR Activation Turns on a Voltage-Gated Inward Current
in Hippocampal Pyramidal Cells. J. Neurophysiol. 83: 2844-2853, 2000. A unique property of the group
I metabotropic glutamate receptor (mGluR)-induced depolarization in
hippocampal cells is that the amplitude of the depolarization is larger
when the response is elicited at more depolarized membrane potentials.
Our understanding of the conductance mechanism underlying this
voltage-dependent response is incomplete. Through the use of
current-clamp and single-electrode voltage-clamp recordings in guinea
pig hippocampal slices, we examined the group I mGluR-induced
depolarization in CA3 pyramidal cells. The group I mGluR agonists
(S)-3-hydroxyphenylglycine and (S)-3,5-dihydroxyphenylglycine turned on a voltage-gated
inward current (ImGluR(V)), which was
pharmacologically distinct from the voltage-gated sodium and calcium
currents intrinsic to the cells. ImGluR(V)
was a slowly activating, noninactivating current with a threshold at
about
75 mV. In addition to the activation of
ImGluR(V), group I mGluR stimulation also
produced a voltage-independent decrease in the K+
conductance. Our results suggest that the depolarization induced by
group I mGluR activation is generated by two ionic mechanisms
a heretofore unrecognized voltage-gated inward current
(ImGluR(V)) that is turned on by
depolarization and a voltage-insensitive inward current that results
from a turn-off of the K+ conductance. The low-threshold
and noninactivating properties of ImGluR(V)
allow the current to play a significant role in setting the resting
potential and firing pattern of CA3 pyramidal cells.
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