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Predominance of the alpha 1D subunit in L-type voltage-gated Ca2+ channels of hair cells in the chicken's cochlea

Kollmar, R., Montgomery, L.G., Fak, J., Henry, L.J., Hudspeth, A.J.
Proceedings of the National Academy of Sciences of the United States of America 1997 v.94 no.26 pp. 14883-14888
chickens, complementary DNA, nucleotide sequences, amino acid sequences, messenger RNA, gene expression, ears, cells, membrane proteins, calcium channels
The voltage-gated Ca2+ channels that effect tonic release of neurotransmitter from hair cells have unusual pharmacological properties: unlike most presynaptic, Ca2+ channels, they are sensitive to dihydropyridines and therefore are L-type. To characterize these Ca2+ channels, we investigated the expression of L-type alpha 1 subunits in hair cells of the chicken's cochlea. In PCRs with five different pairs of degenerate primers, we always obtained alpha 1D products, but only once an alpha 1S product and never an alpha 1S product. A full-length alpha 1D mRNA sequence was assembled from overlapping PCR products; the predicted amino acid sequence of the alpha 1D subunit was about 90% identical to those of the mammalian alpha 1D subunits. In situ hybridization confirmed that the alpha 1D mRNA is present in hair cells. By using a quantitative PCR assay, we determined that the alpha 1D mRNA is 100-500 times more abundant than the alpha 1C mRNA. We conclude that most, if not all voltage-gated Ca2+ channels in hair cells contain an alpha 1D subunit. Furthermore, we propose that the alpha 1D subunit plays a hitherto undocumented role at tonic synapses.