Abstract
L-glutamate is the major excitatory neurotransmitter in the verteb- rate central nervous system. Ionotropic glutamate receptors are divided into three subtypes, AMPA, kainate and NMDA receptors. Oreochomis mossambicus expresses eight AMPA receptor subunits (fGluR1?α、fGluR1?4β), and the electrophysiological properties of the expressed fGluR3α(i) ( i and o respectively represent flip and flop form ) were similar to those of the mammalian flip form AMPA receptors. In this study we found that the electrophysiological properties of fGluR1α(i) are different from those of fGluR3α(i). They differed in (1) the relative current amplitudes activated by various agonists, (2) the affinities to kainate affected by cyclothiazide, and (3) the degrees of desensitization inhibited by cyclothiazide. These differences probably resulted from ligand binding properties and the degrees of receptor desensitization. To explore these possibilities, we generated two chimeras : fGluR1α/3α(i), consisting of the fGluR1α□ backbone with a portion of the S2 domain and flip region of fGluR3α and fGluR3α/1α(i) consisting of the fGluR3α backbone with a portion of the S2 domain and the flip region of fGluR1α. Electrophysiological analyses showed that the properties of fGluR1α/3α(i) were similar to those of fGluR3(i) where as the properties of fGluR3α/1α(i) were similar to those of fGluR1α(i), suggested that different properties between fGluR1α(i) and fGluR3α(i) mainly resulted from the replaced regions. Furthermore, the electro- physiological properties of fGluR3(i) and fGluR3(o) differed only inthe degrees of cyclothiazide inhibited desensitization. Hence it was unlikely that the Asn of the fGluR1α(i) was responsible for the different properties between fGluR1α(i) and fGluR3α(i).