Fig. 2.

The β subunit in bird cochlea. A, Total RNA was extracted from quail cochlear tissue as described in Materials and Methods and was screened for the presence ofslo-β RNA using a single-step RT-PCR assay.Lane 1 is a single round RT-PCR product from quail cochlear tissue; lane 2 is the control experiment, which lacked reverse transcriptase enzyme. The band in lane 1corresponding to ∼800 bp is the expected size of theslo-β product between the two primers.B, The phylogenetic tree for β subunits of BK channels shows that the avian isoforms are nearly identical to each other and that mammalian isoforms have significant homology. However, mammalian and avian β subunits shared only 41% of the amino acids.C, Bovine β subunits had an effect that was qualitatively like that of quail β subunits on α₀. Thebar plot shows the half-activation voltage at 5 μm Ca²⁺ and the time constant of deactivation of tails at −100 mV membrane potential at 5 μm Ca²⁺ for α₀co-expressed independently with quail or bovine β subunits.Open bars show the shift inV_1/2 when comparing α₀ alone with α₀β. Filled bars show the change in the deactivation time constant of α₀β channels as a ratio with that of α₀ alone. The change in steady-state and kinetic parameters attributable to β addition was larger withslo-β_bovine than withslo-β_quail.