Evaluation and comparison of ion permeation and agonist selectivities for N-methyl-d-aspartate receptor channels with different subunit compositions in bilayer lipid membranes based on integrated single-channel currents.
To quantify the ion-permeation ability of the recombinant epsilon1-4/zeta1 channel activated by agonists, the magnitude of agonist-induced integrated single-channel currents for the epsilon2-4/zeta1 N-methyl-d-aspartate (NMDA) channels in bilayer lipid membranes (BLMs) was evaluated electrochemically based on the single-channel recordings. The recombinant epsilon2-4/zeta1 channels were purified from Chinese hamster ovary cells expressing each channel and incorporated in BLMs formed by the tip-dip method. Three typical agonists, l-glutamate, NMDA, and (2S, 3R, 4S) isomer of 2-(carboxycyclopropyl)glycine (l-CCG-IV), were investigated at a concentration of 50 microM. The magnitude of l-glutamate-induced integrated current was found to depend on the epsilon-subunit composition and to increase in the order of epsilon2/zeta1 > epsilon1/zeta1 approximately epsilon4/zeta1 > epsilon3/zeta1, which differs from that of the reported binding affinities (EC(50)) between l-glutamate and each channel type. On the other hand, the magnitude of the integrated currents induced by NMDA and l-CCG-IV did not vary among the four channel types. The order of agonist selectivity toward the epsilon2-4/zeta1 channels in terms of the magnitude of the integrated current was l-glutamate > l-CCG-IV approximately NMDA for the epsilon2/zeta1 channel, l-CCG-IV > NMDA > l-glutamate for the epsilon3/zeta1 channel, and l-CCG-IV approximately l-glutamate > NMDA for the epsilon4/zeta1 channel, suggesting that the agonist selectivity also depends on the epsilon-subunit composition. The present study shows that each epsilon1-4/zeta1 channel has its own ability of ion permeation, i.e., its own signal transduction ability, which is not parallel to its binding ability.
Hirano
A
A
Department of Chemistry, College of Humanities and Sciences, Nihon University, Sakurajosui, Setagaya-ku, Tokyo, 156-8550, Japan.
Wakabayashi
M
M
Sugawara
M
M
Uchino
S
S
Nakajima-Iijima
S
S
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005069:Evaluation Studies as Topic; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D008051:Lipid Bilayers; D016202:N-Methylaspartate / Q000378:metabolism*; D010539:Permeability / Q000187:drug effects; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
D018690:Excitatory Amino Acid Agonists; D008051:Lipid Bilayers; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016202:N-Methylaspartate