Calcium channel subunits in the mouse cochlea

Messages for subunits of voltage-gated calcium channels were examined in the cochlea of the CBA(J) mouse by PCR analysis. Total RNA was extracted from the auditory organs of 16-18-day-old animals. After reverse transcription, resulting cDNA was amplified by PCR with primers targeted to nucleotide sequences corresponding to 12 different calcium channel subunits. PCR products representing subunit gene expression were strongly and consistently amplified for α(1C), α(1D), α(1E), α₂δ, β₁, β₃, and β₄ but not for α(1A), α(1B), α(1S), β₂, γ. The chosen primers amplified cochlear cDNA to yield an overall pattern of bands different from that of any tissue studied thus far, in particular with respect to the α₂δ and β₁ subunits; the α₂δ product was found to be significantly shorter than the corresponding brain and skeletal muscle isoforms. Nucleotide sequencing confirmed the identity of mouse cochlear subunit cDNAs. The results suggest that L-type and presumptive R-type calcium channels are expressed in the mammalian cochlea and that the α₂δ subunits may be coded by a characteristic splice-variant mRNA.