Transcript scanning reveals novel and extensive splice variations in human l-type voltage-gated calcium channel, Cav1.2 alpha1 subunit

Abstract

The L-type (Cav1.2) voltage-gated calcium channels play critical roles in membrane excitability, gene expression, and muscle contraction. The generation of splice variants by the alternative splicing of the poreforming Cav1.2 alpha1-subunit (alpha(1)1.2) may thereby provide potent means to enrich functional diversity. To date, however, no comprehensive scan of alpha(1)1.2 splice variation has been performed, particularly in the human context. Here we have undertaken such a screen, exploiting recently developed "transcript scanning" methods to probe the human gene. The degree of variation turns out to be surprisingly large; 19 of the 55 exons comprising the human alpha(1)1.2 gene were subjected to alternative splicing. Two of these are previously unrecognized exons and two others were not known to be spliced. Comparisons of fetal and adult heart and brain uncovered a large IVS3-S4 variability resulting from combinatorial utilization of exons 31-33. Electrophysiological characterization of such IVS3-S4 variation revealed unmistakable shifts in the voltage dependence of activation, according to an interesting correlation between increased IVS3-S4 linker length and activation at more depolarized potentials. Steady-state inactivation profiles remained unaltered. This systematic portrait of splice variation furnishes a reference library for comprehending combinatorial arrangements of Cav1.2 splice exons, especially as they impact development, physiology, and disease.