Calcium Channel Subunits in the Mouse Cochlea

Abstract

Messages for subunits of voltage-gated calcium channels were examined in the cochlea of the CBAm ouse 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 aic, a 10, alE, /3~,/33, and /3~but not for alA, aiB, ais, /32, or y. 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 a25 and /3s ubunits; the a26 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 a25 subunits may be coded by a characteristic splice-variant mRNA.

Alternative Splicing of the CaV1.3 Channel IQ Domain, a Molecular Switch for Ca2+-Dependent Inactivation within Auditory Hair Cells

“…Likewise, Song et al (2003) and others have suggested that muted CDI may partially arise from ␣ 1 subunit association with different auxiliary subunits (␣ 2 ␦ and ␤) or presynaptic proteins. Previous reports showed that the mouse cochlea expressed Ca V 1.2, Ca V 1.3, Ca V 2.3, and auxiliary subunits ␣ 2 ␦, ␤ 1 , ␤ 3 , and ␤ 4 (Green et al, 1996;Song et al, 2003). The auxiliary subunits when coexpressed with the ␣ 1 subunits modulate the kinetics and properties of channel gating (Lacerda et al, 1991;Singer et al, 1991;Varadi et al, 1991).…”

“…Previous studies proposed that Ca V 1.3 splice variants may be involved (Green et al, 1996;Kollmar et al, 1997a,b;Ramakrishnan et al, 2002). In particular, Ca V 1.3 of the chicken basilar papilla (Kollmar et al, 1997a,b) has an additional 26 amino acids within the I-II loop region (exon 9a) of Ca V 1.3, and the I-II loop has been proposed as a "hinged lid" to obstruct the channel pore and bring about inactivation.…”

“…The auxiliary subunits when coexpressed with the ␣ 1 subunits modulate the kinetics and properties of channel gating (Lacerda et al, 1991;Singer et al, 1991;Varadi et al, 1991). However, in all of these previous screens, either no explicit functional confirmation of altered CDI was performed (Green et al, 1996;Kollmar et al, 1997a,b;Ramakrishnan et al, 2002), or the blunting of CDI was insufficient to explain the profile of native channels (Song et al, 2003). It has been shown that alternative splicing of the Ca V 1.2 gene (Soldatov et al, 1997;Zuhlke and Reuter, 1998;Zuhlke et al, 2000;Tang et al, 2004) contributed to functional diversity of these L-type channels.…”

Functional Interaction of Auxiliary Subunits and Synaptic Proteins With CaV1.3 May Impart Hair Cell Ca2+Current Properties

“…Our goal was to test whether known Ca 2ϩ channel subunits that can be expressed functionally are sufficient to produce the properties of L-type current in hair cells. The ␤ 1A subunit is expressed abundantly in hair cells, but ␤ 2A is not (Green et al 1996). To allow detection of transfected cells, the S65T bright green fluorescent protein (GFP) mutant in GFPpRK5 vector was used to co-transfect the cells to quantify the transfection efficiency.…”

L-type calcium channels in the auditory system

“…Both phenomena exacerbate with age, and are associated, for instance, with impaired speech intelligibility. Studies of the inner ear revealed expression of Ca v 1.2 in the auditory nerve and inhibitory efferents projecting to the OHCs [11,31].…”