The ability of excitatory amino acids to induce increases in the intracellular Ca2+concentration ([Ca2+]i) of cerebellar Purkinje cells was examined by digital fluorescence ratio imaging of voltage-clamped Purkinje cells dialyzed with the Ca2+indicator fura-2. Purkinje cells responded with large inward currents accompanied by increases in dendritic [Ca2+]i, when challenged with the excitatory amino acid agonists glutamate and quisqualate. The rise in [Ca2+]iwas transient and reached peak values of several hundred nanomolar. The response subsisted in the absence of extracellular Ca2+, a condition that eliminates Ca2+entry through voltage-gated Ca2+channels, indicating that Ca2+arose in large part from an intracellular compartment. In support of this hypothesis, only the first agonist application elicited a [Ca2+]iincrease in slices maintained in Ca2+-free medium, as expected if the intracellular stores become depleted. These results indicate that metabotropic glutamate receptors are functional in Purkinje cells and point to glutamate as a possible modulator of [Ca2+]iin these neurons. © 1991.
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