抄録
To analyze precise localization, number and density of functional membrane molecules at the electron microscopic level, we have established a new approach using SDS freeze-fracture replica labeling (SDS-FRL) method. SDS-FRL enabled us to visualize two-dimensional distribution of various membrane molecules with immunogold labeling. For example, we found different clustering patterns of AMPA, NMDA, kainate, and delta2 receptors in synapses in the rat cerebellum and hippocampus. In the cerebellum, we found AMPA receptors making microclusters in parallel fiber-Purkinje cell synapses with a relatively low density of extrasynaptic receptors. Also, a high variability of AMPA receptor density was observed in these synapses. In climbing fiber-Purkinje cell synapses, AMPA receptors were distributed in a much more homogeneous manner. Combination of electrophysiological measurements of functional AMPA receptors and SDS-FRL revealed that one gold particle for AMPA receptor can roughly represent one functional channel in immature rat climbing fiber-Purkinje cell synapses. In hippocampal CA1 pyramidal cell synapses, AMPA receptors were clustered with a high variability of density in synapses and were distributed in extrasynaptic sites with much higher density than that in the Purkinje cells. NMDA receptors also made clusters in these synapses but with a lower variability of density and a lower relative density in extrasynaptic sites. These results indicate distinct regulation of clustering of ionotropic glutamate receptors between different subunits and cell types. [Jpn J Physiol 54 Suppl:S2 (2004)]
