Figure 2. Cerebellar granule cells show a fast inward current upon 5-HT₃ receptor activation with a characteristic voltage-dependent Ca²⁺ block.

A, P7 granule cell used for electrophysiological recordings, showing a mature morphology. Ba, physiological characteristics of the recorded granule cells were less mature, with occasionally one spike at the beginning of depolarization steps. Bb, protocol of injected current steps used for Ba. C, examples of a 5-HT₃ receptor-mediated response to local application of 100 μm 5-HT (Ca) and 100 μm SR57227A (Cb) for 500 ms. D, I–V curve of the 5-HT₃ receptor-mediated ion current shows the characteristic voltage-dependent Ca²⁺ block.