Splicing for alternative structures of Cav1.2 Ca2+ channels in cardiac and smooth muscles.

An estimate of up to 60% of genes are subjected to alternative splicing, and 15% of human genetic diseases are associated with mutation of the splice sites [Krawczak M, Reiss J, and Cooper DN. The mutational spectrum of single base-pair substitutions in mRNA splice junctions of human genes: causes and consequences. Hum Genet 1992; 90: 41-54; Cooper TA, and Mattox W. The regulation of splice-site selection, and its role in human disease. Am J Hum Genet 1997; 61: 259-66; Modrek B and Lee CJ. Alternative splicing in the human, mouse and rat genomes is associated with an increased frequency of exon creation and/or loss. Nat Genet 2003; 34: 177-80; Modrek B, Resch A, Grasso C, and Lee C. Genome-wide detection of alternative splicing in expressed sequences of human genes. Nucleic Acids Res 2001; 29: 2850-9; Lander ES, Linton LM, Birren B, Nusbaum C, Zody MC, Baldwin J, et al. Initial sequencing and analysis of the human genome. Nature 2001; 409: 860-921] . The molecular diversity of alternatively spliced transcripts provides templates for a myriad of protein structures that are potentially crucial to sustaining the complexity of human physiology. The extensive alternative splicing of the alpha(1)1.2-subunit of the L-type Ca(v)1.2 channel, producing splice variants with distinct electrophysiological and pharmacological properties, would impact directly on the function of the cardiovascular system. Cell-selective expression of Ca(v)1.2 channels containing a specific alternatively spliced exon increases the functional variations for specific cellular activities in response to changing physiological signals. However, the regulation or control of the alpha(1)1.2-subunit alternative splicing machinery is unknown, and the role of numerous splice variants expressed in a cell is a mystery. A systematic and concerted effort is required to determine all the possible combinations of alternatively spliced exons in alpha(1)1.2-subunits in smooth and cardiac muscles. This will provide useful information to monitor changes on the usage of the entire suite of alternatively spliced exons to help relate altered Ca(v)1.2 channel function to physiology and disease.