Pharmacologically distinct glutamate receptors on cerebellar granule cells

Cultured cerebellar granule cells were found to exhibit calcium-dependent release of 3H-D-aspartate when stimulated with excitatory amino acids. L-glutamate and L-aspartate were found to be potent stimulators of 3H-D-aspartate release, D-aspartate was weaker and only minor effects were seen with D-glutamate, quisqualate, kainate, N-methyl-D-aspartate (NMDA) and L-alpha-aminoadipate (L-alpha AA). It was also found that only L-glutamate and L-aspartate showed high affinity for the 3H-L-glutamate binding sites on granule cell membranes. Stimulation by L-glutamate of 3H-D-aspartate release could be blocked by various excitatory amino acid antagonists. From the relative potencies of agonists and antagonists on D-aspartate release it is suggested that cerebellar granule cells express functionally active glutamate receptors with pharmacological characteristics different from all known excitatory amino acid receptors.