Ionic basis of membrane potential in outer hair cells of guinea pig cochlea

Mammalian hearing involves features not found in other species, for example,the separation of sound frequencies depends on an active control of the cochlear mechanics1,2.The force-generating component in the cochlea is likely to be the outer hair cell(OHC), one of the two types of sensory cell through which current is gated by mechano-electrical transducer channels sited on the apical surface3.Outer hair cells isolated in vitro have been shown to be motile4,5 and capable of generating forces at acoustic frequencies6. The OHC membrane is not, however, electrically tuned, as found in lower vertebrates7–9. Here we describe how the OHC resting potential is determined by a Ca2+-activated K+ conductance10,11 at the base of the cell. Two channel types with unitary sizes of 240 and 45 pS underlie this Ca2+-activated K+ conductance and we suggest that their activity is determined by a Ca2+ influx through the apical transducer channel, as demonstrated in other hair cells12. This coupled system simultaneously explains the large OHC resting potentials observed in vivo13,14 and indicates how the current gated by the transducer may be maximized to generate the forces required in cochlear micromechanics.