Hisashi Mori

Cloning and expression of the ε4 subunit of the NMDA receptor channel

The primary structure of a novel subunit of the mouse NMDA (N‐methyl‐d‐aspartate) receptor channel, designated ε4, has been revealed by cloning and sequencing the cDNA. The ε4 subunit shares high amino acid sequence identity with the ε1, ε2 and ε3 subunits of the mouse NMDA. receptor channel, thus constituting the ε subfamily of the glutamate receptor channel. Expression from cloned cDNAs of the ε4 subunit together with the ζ1 subunit in Xenopus oocytes yields Functional NMDA receptor channels. The ε4/ζ1 heteromeric channel exhibits high apparent affinities for agonists and low sensitivities to competitive antagonists. The ε4 subunit is thus distinct in Functional properties from the ε1, ε2 and ε3 subunits, and contributes further diversity of the NMDA receptor channel.

Cloning, expression and modulation of a mouse NMDA receptor subunit

The primary structure and presence of two forms of the mouse N‐methyl‐d‐aspartate (NMDA) receptor channel subunit ζl have been disclosed by cloning and sequencing the cDNAs. The ζl subunit shows −20% amino acid sequence identities with the rodent α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA)‐ or kainate‐selective GluR subunits and has structural features common to neurotransmitter‐gated ion channels. Functional homomeric ζl channels expressed in Xenopus oocytes by injection of the subunit specific mRNA exhibit current responses characteristics for the NMDA receptor channel such as activation by glycine, Ca2+ permeability, blocking by Mg2+ and activation by polyamine. It has been found that the ζl channel activity is positively modulated by treatment with 12‐O‐tetradecanoylphorbol 13‐acetate (TPA).

A single amino acid residue determines the Ca2+ permeability of AMPA-selective glutamate receptor channels

Functional analysis of AMPA-selective glutamate receptor channels expressed in Xenopus oocytes from cloned cDNAs has shown that homomeric channels formed by the GluR1 subunit are permeable to Ca2+, whereas heteromeric channels composed of the GluR1 and GluR2 subunits show little permeability. Furthermore, substitution of glutamine for arginine in putative transmembrane segment M2 of the GluR2 subunit makes the heteromeric channels permeable to Ca2+. These results suggest that the GluR2 subunit plays a key role in keeping AMPA-selective glutamate receptor channels essentially impermeable to Ca2+ and that the critical determinant is the positively charged residue in M2 segment.

Ion permeation properties of the cloned mouse ϵ2/ζ1 NMDA receptor channel

Abstract The heteromeric mouse ϵ2/ζ1 N- methyl - d - aspartate (NMDA) receptor was expressed in Xenopus oocytes, and its channel properties were studied using both the outside-out patch-clamp and two-microelectrode voltage-clamp techniques. In the cloned receptor channel, permeation properties of monovulent and divalent cations, and voltage-dependent block by Mg2+ were similar to those reported previously in the native NMDA receptor channels. The sequence of single-channel conductances for alkali metals was Rb+ > Cs+ ≈ K+ > Na+ > Li+, whereas the sequence of relative permeabilities was Cs+ > Rb+ > K+ ≈ Na+ > Li+. The single-channel conductances measured in isotonic Ca2+, Sr2+ and Ba2+ solutions were almost equal, and approximately one-fifth of the value in the Na+ solution, although the permeabilities for these alkaline earth cations were higher than for Na+. It is likely that Ca2+, Sr2+ and Ba2+ would enter the NMDA receptor channel more easily than Na+, but would bind to a site in the channel more tightly, the net effect being a reduced value of the current.