Figure 3: Molecular diversity of Cav1.2. (a) Transmembrane topology of the Cav1.2 subunit in schematic diagram. Four regions of homology (I–IV), each composed of 6 transmembrane segments (numbered), are folded around the central pore. The polypeptide sequence is segmented by black bars and sequentially numbered (1–50) according to the CACNA1C genomic map . The segments corresponding to the invariant (black/gray) and alternative (blue) exons are outlined. α-interaction domain (AID) of a constitutive β-binding is shown in green. In the CaM-binding domain (CBD), apo-CaM and Ca2+-CaM are shared between LA and IQ motifs (red), respectively. (b) Alternative splicing of human fibroblast CACNA1C in the region of exons 20–46. The following splice variants were studied: (GenBank #z34809, splice variant lacking alternative exons (Δ) 21, 32, 41A, and 45), (z34810, Δ 22, 31, 41A, and 45), (z34811, Δ 22, 31, and 45), (z34812, Δ 22, 31, 33, and 45), (z34814, Δ 21, 31, 33, 41A, and 45), and (z34815, Δ 21, 31, 41A, and 45).