Two novel subunits of the mouse NMDA receptor channel, the epsilon 2 and epsilon 3 subunits, have been identified by cloning and expression of complementary DNAs. The heteromeric epsilon 1/zeta 1, epsilon 2/zeta 1 and epsilon 3/zeta 1 NMDA receptor channels exhibit distinct functional properties in affinities for agonists and sensitivities to competitive antagonists and Mg2+ block. In contrast to the wide distribution of the epsilon 1 and zeta 1 subunit messenger RNAs in the brain, the epsilon 2 subunit mRNA is expressed only in the forebrain and the epsilon 3 subunit mRNA is found predominantly in the cerebellum. The epsilon 1/zeta 1 and epsilon 2/zeta 1 channels expressed in Xenopus oocytes, but not the epsilon 3/zeta 1 channel, are activated by treatment with 12-O-tetradecanoylphorbol 13-acetate. These findings suggest that the molecular diversity of the epsilon subunit family underlies the functional heterogeneity of the NMDA receptor channel.

The glutamate receptor (GluR) channel plays a key part in brain function. Among GluR channel subtypes, the NMDA (N-methyl-D-aspartate) receptor channel which is highly permeable to Ca2+ is essential for the synaptic plasticity underlying memory, learning and development. Furthermore, abnormal activation of the NMDA receptor channel may trigger the neuronal cell death observed in various brain disorders. A complementary DNA encoding a subunit of the rodent NMDA receptor channel (NMDAR1 or zeta 1) has been cloned and its functional properties investigated. Here we report the identification and primary structure of a novel mouse NMDA receptor channel subunit, designated as epsilon 1, after cloning and sequencing the cDNA. The epsilon 1 subunit shows 11-18% amino-acid sequence identity with rodent GluR channel subunits that have been characterized so far and has structural features common to neurotransmitter-gated ion channels. Expression from cloned cDNAs of the epsilon 1 subunit together with the zeta 1 subunit in Xenopus oocytes yields functional GluR channels with high activity and characteristics of the NMDA receptor channel. Furthermore, the heteromeric NMDA receptor channel can be activated by glycine alone.

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The complete amino acid sequences of two mouse glutamate receptor subunits (GluRl and GluR2) have been deduced by cloning and sequencing the cDNAs. Xenopus oocytes injected with mRNA derived from the GluRl cDNA exhibit current responses both to kainate and to quisqualate as well as to glutamate, whereas oocytes injected with mRNA derived from the GluR2 cDNA show little response. Injection of oocytes with both the mRNAs produces current responses larger than those induced by the GluRl-specific mRNA and the dose-response relations indicate a positively cooperative interaction between the two subunits. These results suggest that kainate and quisqualate can activate a common glutamate receptor subtype and that glutamate-gated ionic channels are hetero-oligomers of different subunits.

Activation of blood cells during hemodialysis is considered to be a significant determinant of biocompatibility of the hemodialysis membrane because it may affect patient health adversely through microvascular inflammation and oxidative stress. This study found very different cell activation among various polysulfone (PSf) hemodialysis membranes. For example, CX‐U, a conventional PSf membrane, induced marked adhesion of platelets to its surface and increased surface expression of activated CD11b and production of reactive oxygen species (ROS) by neutrophils; while NV‐U, a hydrophilic polymer‐immobilized PSf membrane, caused little platelet adhesion and slight CD11b expression and ROS production by neutrophils. Analysis of the molecular mechanisms of the above phenomena on CX‐U and NV‐U indicated that anti‐integrin GPIIb/IIIa antibody blocked platelet adhesion, and that the combination of anti‐CD11b (integrin α subunit of Mac‐1) and anti‐integrin αvβ3 antibodies blocked ROS production by neutrophils. Plasma‐derived fibrinogen, a major ligand of GPIIb/IIIa, Mac‐1, and αvβ3 on membranes, was thus analyzed and found to be more adsorbed to CX‐U than to NV‐U. Moreover, comparison between five PSf membranes showed that the number of adherent platelets and neutrophil ROS production increased with increasing fibrinogen adsorption. These results suggested that fibrinogen, adsorbed on membranes, induced GPIIb/IIIa‐mediated platelet activation and Mac‐1/αvβ3‐mediated neutrophil activation, depending on the amount of adsorption. In conclusion, the use of biocompatible membranes like NV‐U, which show lower adsorption of fibrinogen, is expected to reduce hemodialysis‐induced inflammation and oxidative stress by minimizing cell activation.