Functional Properties of a Newly Identified C-terminal Splice Variant of Cav1.3 L-type Ca2+ Channels

An intramolecular interaction between a distal (DCRD) and a proximal regulatory domain (PCRD) within theCterminus of long Ca(v)1.3 L-type Ca2+ channels (Cav1.3(L)) is a major determinant of their voltage-and Ca2+-dependent gating kinetics. Removal of these regulatory domains by alternative splicing generates Ca(v)1.3(42A) channels that activate at a more negative voltage range and exhibit more pronounced Ca2+-dependent inactivation. Here we describe the discovery of a novel short splice variant (Ca(v)1.3(43S)) that is expressed at high levels in the brain but not in the heart. It lacks the DCRD but, in contrast to Ca(v)1.3(42A), still contains PCRD. When expressed together with alpha 2 delta 1 and beta 3 subunits in tsA-201 cells, Ca(v)1.3(43S) also activated at more negative voltages like Ca(v)1.3(42A) but Ca2+-dependent inactivation was less pronounced. Single channel recordings revealed much higher channel open probabilities for both short splice variants as compared with Ca(v)1.3(L). The presence of the proximal C terminus in Ca(v)1.3(43S) channels preserved their modulation by distal C terminus-containing Ca(v)1.3- and Ca(v)1.2-derived C-terminal peptides. Removal of the C-terminal modulation by alternative splicing also induced a faster decay of Ca2+ influx during electrical activities mimicking trains of neuronal action potentials. Our findings extend the spectrum of functionally diverse Ca(v)1.3 L-type channels produced by tissue-specific alternative splicing. This diversity may help to fine tune Ca2+ channel signaling and, in the case of short variants lacking a functional C-terminal modulation, prevent excessive Ca2+ accumulation during burst firing in neurons. This may be especially important in neurons that are affected by Ca2+-induced neurodegenerative processes.