CaV1.3 channels are unique among the high voltage-activated Ca2+ channel family because they activate at the most negative potentials and display very rapid calcium-dependent inactivation. Both properties are of crucial importance in neurons of the suprachiasmatic nucleus and substantia nigra, where the influx of Ca2+ ions at subthreshold membrane voltages supports pacemaking function. Previously, alternative splicing in the CaV1.3 C terminus gives rise to a long (CaV1.342) and a short form (CaV1.342A), resulting in a pronounced activation at more negative voltages and faster inactivation in the latter. It was further shown that the C-terminal modulator in the CaV1.342 isoforms modulates calmodulin binding to the IQ domain. Using splice variant-specific antibodies, we determined that protein localization of both splice variants in different brain regions were similar. Using the transcript-scanning method, we further identified alternative splicing at four loci in the C terminus of CaV1.3 channels. Alternative splicing of exon 41 removes the IQ motif, resulting in a truncated CaV1.3 protein with diminished inactivation. Splicing of exon 43 causes a frameshift and exhibits a robust inactivation of similar intensity to CaV1.342A. Alternative splicing of exons 44 and 48 are in-frame, altering interaction of the distal modulator with the IQ domain and tapering inactivation slightly. Thus, alternative splicing in the C terminus of CaV1.3 channels modulates its electrophysiological properties, which could in turn alter neuronal firing properties and functions.
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