Membrane depolarization and the expression of glutamate receptors in cerebellar granule cells

The functional expression of glutamate receptors in cerebellar granule cells in culture was examined using the whole-cell patch clamp technique. All the cells tested responded with an inward current to superfusion with glutamate, kainate, or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate. Neurones cultured in a medium containing an elevated K+ concentration (25 mM) responded to N-methyl-D-aspartate (NMDA) provided they were simultaneously exposed to glycine (Gly). In contrast, NMDA/Gly-evoked currents were virtually undetectable in cells grown in medium containing ‘low’ K+ (10 mM), suggesting that only the NMDA-preferring class of glutamate receptors are subject to up-regulation by K+-induced chronic membrane depolarization.