A, exon 33L contains an additional 71 nt that are 5′ to exon 33, encoding 22 amino acids with a frameshift. The canonical acceptors -ag- for exon 33L and -AG- for exon 33 are labeled in boxes. B, with the presence of either mutually exclusive exons 31 or 32, a stop codon is generated in exon 33L. C, exon 33L containing the Cav1.2 channel is truncated with the deletion of IVS4 and downstream entire C terminus.