Alternative Splicing of the Voltage-Gated Ca²⁺ Channel β₄ Subunit Creates a Uniquely Folded N-Terminal Protein Binding Domain with Cell-Specific Expression in the Cerebellar Cortex

Distribution of β subunit subtypes in mouse cerebellum. A, Splice variant-specific antibodies were created against unique β_4a and β_4b sequences (highlighted). B, Western blot showing that β_4a-, β_4b-, and β₃-specific antibodies recognize 52–55 kDa proteins in sucrose step gradient-purified mouse cerebellar membranes. Numbers to the left indicate molecular mass in kilodaltons. C, Purkinje cells labeled with anti-calbindin antibody (scale bar, 20 μm) serve to distinguish the molecular (ML), Purkinje cell (PCL), and granule cell (GCL) layers (for orientation in D–G). D, E, Punctate labeling of the β_4a subunit in the molecular layer of the cerebellum: D, confocal microscopy, 1-μm-thick image; E, light microscopy, 50-μm-thick section. F, The β_4b subunit is expressed in Purkinje cell bodies and Bergman glia. G, The β₃ subunit is expressed in basket cell structures surrounding Purkinje cell bodies and in granule cell layer puncta. Inset, Higher-power image (scale bar, 10 μm) of basket cell labeling (supplemental Fig. 2, available at www.jneurosci.org as supplemental material).