cSlo encodes calcium-activated potassium channels in the chick's cochlea

Large conductance, calcium-activated (BK) potassium channels play a central role in the excitability of cochlear hair cells. In mammalian brains, one class of these channels, termed Slo, is encoded by homologues of the Drosophila 'slowpoke' gene. By homology screening with mouse Slo cDNA, we have isolated a full-length clone (cSlo1) from a chick's cochlear cDNA library. cSlo1 had greater than 90% identity with mouse Slo at the amino acid level, and was even better matched to a human brain Slo at the amino and carboxy termini. cSlo1 had none of the additional exons found in splice variants from mammalian brain. The reverse transcriptase polymerase chain reaction (RT-PCR) was used to show expression of cSlo1 in the microdissected hair cell epithelium (basilar papilla). Transient transfection of HEK 293 cells demonstrated that cSlo1 encoded a potassium channel whose conductance averaged 224 pS at +60 mV in symmetrical 140 mM K⁺. Macroscopic currents through cSlo1 channels were blocked by scorpion toxin or tetraethyl ammonium, and were voltage and calcium dependent. cSlo1 is likely to encode BK-type calcium-activated potassium channels in cochlear hair cells.