Ca(2+) permeation of AMPA receptors in cerebellar neurons expressing glu receptor 2.

AMPA receptors in cultured cerebellar neurons were characterized by whole-cell electrophysiological studies and single cell PCR-based quantitation of subunit mRNA expression. Purkinje neurons consistently expressed high levels of Glu receptor 2 (GluR2) mRNA and AMPA receptors with low but nonzero Ca(2+) permeability. Other cerebellar neurons expressed AMPA receptors with a wide range of Ca(2+) permeability and of fractional GluR2. These properties correlated on a cell-by-cell basis. Their relationship was well fit by a model that assumed stochastic assembly of subunits and GluR2 dominance in controlling divalent cation permeation, suggesting that AMPA receptor properties in individual neurons may be determined primarily by relative levels of subunit transcription. A fraction of receptors, lacking GluR2, can contribute a highly Ca(2+)-permeable component to AMPA receptor responses, even in cells expressing GluR2.