Cloning and developmental expression of Shaker potassium channels in the cochlea of the chicken

Signal coding by the receptor and neuronal cells of the auditory system involves various ion channels that modulate a sound stimulus. The genes that encode a number of these ion channels and their accessory subunits are presently unknown for channels found in the sensory epithelium and cochlear nerve. Among these genes are those that encode delayed rectifier and transient type potassium channels found in both the sensory cells and the ganglion. Here, we report the cloning and developmental expression of Shaker family members that include cKv1.2, cKv1.3, cKv1.5, and the Shaker-related cGMP-gated potassium channel cKCNA10. Clones were obtained by screening a chicken embryonic cochlea cDNA library using, as a probe, a mixture of two DNA fragments of cKv1.2 and cKv1.3 obtained by the reverse transcription polymerase chain reaction (RT-PCR). Sequence analysis revealed chicken homologues of Kv1.2, Kv1.3, Kv1.5 and cGMP-gated potassium channels with a deduced amino acid homology of 96-98%, 82-84%, 67-71% and 67-79% to correspondent mammalian homologues. During development of chicken inner ear, RT-PCR studies show expression of cKv1.2, cKv1.3 and cKv1.5 as early as Embryonic Day (ED) 3, while cKCNA10 was detected at low levels beginning on ED6 and was highly expressed by ED9. Additionally, analysis of expression in different parts of the cochlea showed that these genes were co-expressed in different regions of the cochlea, including the cochlear ganglion, sensory epithelium, lagena, and tegmentum. This expression pattern suggests the potential for the formation of heteromeric channels from the corresponding alpha-subunits in these various tissues.