The structures of the human calcium channel alpha 1 subunit (CACNL1A2) and beta subunit (CACNLB3) genes

Calcium influx in pancreatic beta-cells is regulated mainly by L-type voltage-dependent calcium channels (VDCCs) and triggers insulin secretion. The alpha 1 subunit (CACN4) and the beta subunit (beta 3) of VDCCs, both of which are expressed in pancreatic islets, are major components for the VDCC activity, and so they may play a critical role in the regulation of insulin secretion. We have determined the structures of the human CACN4 (CACNL1A2) and the human beta 3 (CACNLB3) genes. The CACNL1A2 gene spans more than 155 kb and has 49 exons. Most of the positions interrupted by introns are well conserved between the CACNL1A2 gene and the previously reported L-type VDCC alpha 1 subunit, CACNL1A1, gene. On the other hand, the CACNLB3 gene distributes in approximately 8 kb and comprises 13 exons, most of which are located together within approximately 5 kb. Comparisons of the genomic sequences of CACNL1A2 with the previously reported cDNA sequences indicate that there are a number of polymorphisms in the human CACNL1A2 gene. In addition, the PCR-SSCP procedure of exon 1 of CACNL1A2 revealed a change from 7 to 8 ATG trinucleotide repeats in a patient with non-insulin-dependent diabetes mellitus (NIDDM), resulting in an addition of methionine at the amino-terminus of CACN4. The determination of the structures of the human CACNL1A2 and CACNLB3 genes should facilitate study of the role of these genes in the development of NIDDM and also other genetic diseases such as long QT syndrome.