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
✍ Scribed by Ayumi Hirano; Masaki Wakabayashi; Masao Sugawara; Shigeo Uchino; Sadayo Nakajima-Iijima
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 96 KB
- Volume
- 283
- Category
- Article
- ISSN
- 0003-2697
No coin nor oath required. For personal study only.
✦ Synopsis
To quantify the ion-permeation ability of the recombinant ⑀1-4/1 channel activated by agonists, the magnitude of agonist-induced integrated single-channel currents for the ⑀2-4/1 N-methyl-D-aspartate (NMDA) channels in bilayer lipid membranes (BLMs) was evaluated electrochemically based on the single-channel recordings. The recombinant ⑀2-4/1 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 M. The magnitude of L-glutamate-induced integrated current was found to depend on the ⑀-subunit composition and to increase in the order of ⑀2/1 > ⑀1/1 Ϸ ⑀4/1 > ⑀3/1, 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 ⑀2-4/1 channels in terms of the magnitude of the integrated current was L-glutamate > L-CCG-IV Ϸ NMDA for the ⑀2/1 channel, L-CCG-IV > NMDA > Lglutamate for the ⑀3/1 channel, and L-CCG-IV Ϸ L-glutamate > NMDA for the ⑀4/1 channel, suggesting that the agonist selectivity also depends on the ⑀-subunit composition. The present study shows that each ⑀1-4/1 channel has its own ability of ion permeation, i.e., its own signal transduction ability, which is not parallel to its binding ability.