Novel Ca_v2.1 splice variants isolated from Purkinje cells do not generate P-type Ca²⁺ current

The α₁2.1 (α_1A) subunits of P-type and Q-type Ca²⁺ channels are encoded by a single gene, Cacna1a. Although these channels differ in the inactivation kinetics and sensitivity to ω-agatoxin IVA, the mechanism underlying these differences remains to be clarified. Alternative splicings of the Cacna1a transcript have been postulated to contribute to the respective properties, however, the splice variants responsible for P-type Ca²⁺ channels have not been identified. To explore P-type-specific splice variants, we aimed at cloning _α12.1 from isolated mouse Purkinje cells using single-cell reverse transcription-PCR, because in Purkinje cells P-type currents dominate over the whole currents (>95%) with Q-type currents undetected. As a result, two novel splice variants were cloned. Compared with the previously cloned mouse _α12.1, two novel variants had additional 48 amino acids at the amino termini, six single amino acid changes, and splicing variations at the exon 46/47 boundary, which produced different carboxyl termini. Furthermore, one variant had one RNA editing site. However, electrophysiological and pharmacological studies indicated that these variants did not generate P-type current in cultured cells. These results suggest that P-type-specific splice variants may exist but that post-translational processing or modification by uncharacterized interacting proteins is also required for generating the P-type current.