L-glutamate and acetylcholine mobilise Ca2+ from the same intracellular pool in cerebellar granule cells using transduction mechanisms with different Ca2+ sensitivities.
Ca2+ mobilisation induced by L-glutamate (Glu) and acetylcholine (ACh) has been studied in cultured cerebellar granule cells using digital fluorescence microscopy. The ability of Glu-receptor activation to mobilise Ca2+ was decreased when [Ca2+]o was lowered to 10 microM (from 1.8 mM). It was enhanced when [Ca2+]i was raised using 25 mM external K+ or by N-methyl-D-aspartate (NMDA), which selectively activates a distinct Glu-receptor subtype. The enhancement was dependent on entry of external Ca2+. In contrast, the ability of ACh receptor activation to mobilise Ca2+ was not affected by these conditions. Furthermore, pretreatment with pertussis toxin inhibited Ca2+ mobilisation in response to Glu-receptor activation without affecting mobilisation in response to ACh. However, activation of both receptors mobilised Ca2+ from a common, thapsigargin-sensitive pool. We conclude that there are differences in the Ca2+ mobilization pathways for the two receptor systems in cerebellar granule cells. The Ca(2+)-sensitivity of this Ca2+ mobilizing Glu receptor may have implications for its function in neuronal synaptogenesis and plasticity.