Signature combinatorial splicing profiles of rat cardiac- and smooth-muscle Cav1.2 channels with distinct biophysical properties.

l-type (Ca(v)1.2) voltage-gated calcium channels play an essential role in muscle contraction in the cardiovascular system. Alternative splicing of the pore-forming Ca(v)1.2 subunit provides potent means to enrich the functional diversity of the channels. There are 11 alternatively spliced exons identified in rat Ca(v)1.2 gene and random rearrangements may generate up to hundreds of combinatorial splicing profiles. Due to such complexity, the real combinatorial splicing profiles of Ca(v)1.2 have not been solved. This study investigated whether the 11 alternatively spliced exons are spliced randomly or linked and if linked, how many combinatorial splicing profiles can be arranged in cardiac- and smooth-muscle cells. By examining three full-length cDNA libraries of the Ca(v)1.2 transcripts isolated from rat heart and aorta, our results showed that the arrangements of some of the alternatively spliced exons are tissue-specific and tightly linked, giving rise to only 41 alternative combinatorial profiles, of which 29 have not been reported. Interestingly, the 41 combinatorial profiles were distinctively distributed in the three Ca(v)1.2 libraries and the one named "heart 1-50" contained unexpected splice variants. Significantly, the tissue-specific cardiac- and smooth-muscle combinatorial splicing profiles of Ca(v)1.2 channels demonstrated distinct electrophysiological properties that may help rationalize the differences observed in native currents. The unique sequences in these tissue-specific splice variants may provide the potential targets for drug design and screening.