The functional expression of the kainate subtype of glutamate receptor (GluR) has been investigated in cultured rat cerebellar granule cells using single cell intracellular calcium ([Ca2+]i) measurements. Both AMPA- and kainate-induced [Ca2+]i increases could be blocked completely by the AMPA receptor-selective antagonist LY300168 (50 microM). However, following treatment with concanavalin A, an inhibitor of kainate receptor desensitisation, 30% of cells showed a kainate-induced [Ca2+]i rise of >100 nM in the presence of LY300168. Responses to 30 microM kainate in the presence of LY300168 were virtually abolished by the AMPA and GluR5 kainate receptor competitive antagonist LY293558 (100 microM). These results demonstrate the presence of functional kainate receptors on cultured cerebellar granule cells, and suggest that the GluR5 subtype of kainate receptor plays a significant role in kainate receptor-mediated [Ca2+]i increases.