CSLO ENCODES CALCIUM-ACTIVATED POTASSIUM CHANNELS IN THE CHICKS COCHLEA

Large conductance, calcium-activated (BK) potassium channels play a ce ntral role in the excitability of cochlear hair cells. In mammalian br ains, one class of these channels, termed Slo, is encoded by homologue s of the Drosophila slowpoke' gene. By homology screening with mouse S lo cDNA, we have isolated a full-length clone (cSlo1) from a chick's c ochlear cDNA library. cSlo1 had greater than 90% identity with mouse S lo at the amino acid level, and was even better matched to a human bra in Slo at the amino and carboxy termini. cSlo1 had none of the additio nal exons found in splice variants from mammalian brain. The reverse t ranscriptase polymerase chain reaction (RT-PCR) was used to show expre ssion of cSlo1 in the microdissected hair cell epithelium (basilar pap illa). 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 channe ls were blocked by scorpion toxin or tetraethyl ammonium, and were vol tage and calcium dependent. cSlo1 is likely to encode BK-type calcium- activated potassium channels in cochlear hair cells.