Differential splicing patterns of L-type calcium channel Ca(v)1.2 subunit in hearts of Spontaneously Hypertensive Rats and Wistar Kyoto Rats

Ca(v)1.2 L-type calcium channels are essential in heart and smooth muscle contraction. Rat Ca(v)1.2 gene contains 11 alternatively spliced exons (la, 1, 8a, 8, 9*, 21, 22, 31, 32, 32-6nt and 33) which can be assorted to generate a large number of functionally distinct splice variants. Until now, it is unknown whether the utilization of these alternatively spliced exons is altered in the hypertrophied hearts of hypertensive rats. By comparing the assortments of these 11 exons in full-length Ca(v)1.2 transcripts derived from Spontaneously Hypertensive Rats (SHRs) and Wistar Kyoto Rats (WKYs) hearts, we found that the inclusion of Ca(v)1.2 alternative exons was significantly different between the two rats both at individual loci and in combinatorial arrangements. Functional characterizations of three Ca(v)1.2 channel splice variants that were identified to be significantly altered in SHR hypertrophied cardiomyocytes demonstrated distinct whole-cell electrophysiological properties when expressed in HEK 293 cells. Interestingly, aberrant splice variants which included or excluded both mutually exclusive exons 21/22 or exons 31/32 were found to be increased in hypertensive rats. Two aberrant splice variants that included both exons 21 and 22 were found to be unable to conduct currents even though they expressed proteins with the predicted molecular mass. Characterization of one of the aberrant splice variants showed that it exerted a dominant negative effect on the functional Ca(v)1.2 channels when co-expressed in HEK293 cells. The altered combinatorial splicing profiles of Ca(v)1.2 transcripts identified in SHR hearts provide a different and new perspective in understanding the possible role of molecular remodeling of Ca(v)1.2 channels in cardiac hypertrophy as a consequence of hypertension. (C) 2007 Elsevier B.V. All rights reserved.