Hair cell-specific splicing of mRNA for the α(1D) subunit of voltage-gated Ca(2+) channels in the chicken’s cochlea

The L-type voltage-gated Ca(2+) channels that control tonic release of neurotransmitter from hair cells exhibit unusual electrophysiological properties: a low activation threshold, rapid activation and deactivation, and a lack of Ca(2+)-dependent inactivation. We have inquired whether these characteristics result from cell-specific splicing of the mRNA for the L-type α(1D) subunit that predominates in hair cells of the chicken’s cochlea. The α(1D) subunit in hair cells contains three uncommon exons: one encoding a 26-aa insert in the cytoplasmic loop between repeats I and II, an alternative exon for transmembrane segment IIIS2, and a heretofore undescribed exon specifying a 10-aa insert in the cytoplasmic loop between segments IVS2 and IVS3. We propose that the alternative splicing of the α(1D) mRNA contributes to the unusual behavior of the hair cell’s voltage-gated Ca(2+) channels.