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 Sla cDNA, we have isolated a full-length clone (cSlo1) from a chick's cochlear cDNA library, rSlol 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. cSlol 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 cSlal in the microdissected hair cell epithelium basilar papilla. Transient transfection of HIEK 293 cells demonstrated that cSlol encoded a potassium channel whose conductance averaged 224 pS at +60 mV in symmetrical 140 mM K. Macroscopic currents through cSlol channels were blocked by scorpion toxin or tetraethyl ammonium, and were voltage and calcium dependent. cSlol is likely to encode BK-type calcium-activated potassium channels in cochlear hair cells.