The participation of AMPA receptors in certain neurodegenerative diseases may depend on their Ca2+ permeability. AMPA receptors, which consist of multimetric assemblies of four (or five) subunits, can be divided into two subclasses, those with low (type I) and high Ca2+ permeability (type II). We transfected cDNAs of GluR1 and GluR2 AMPA receptor subunits in varying ratios into HEK293 cells to clarify the subunit ratio-dependence of glutamate responses. An implicit assumption in this study is that levels of protein subunit expression reliably reflect cDNA transfection ratios. Analysis of whole-cell currents generated from co-expression of GluR1 and GluR2 indicated that two functionally distinct receptors are produced (types I and II). When GluR1 and GluR2 were co-transfected in a 4:1 ratio, the resulting whole-cell current traces exhibited properties that were a mixture of those of type I and type II receptors. The experimental system of quantitative subunit protein expression developed in this study is useful for electrophysiological study of AMPA receptor functions.

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