Later work proved that the resonant frequency was set by the density and kinetics of potassium channels, the frequency increasing with a greater number of faster channels. At least three classes of potassium channels are needed to cover the range of hearing: voltage- and calcium-activated (BK) channels, voltage-gated (Kv) channels, and inwardly rectifying channels. These channels work together with voltage-gated calcium channels to generate electrical resonance, a conclusion that was supported by mathematical reconstruction and simulations.[3] This mechanism is present in all vertebrate classes except mammals.
Another important development was the use of new methods of imaging hair cell stereociliary bundles and delivering force stimuli, providing the first demonstration of sub-micron active oscillations of the bundles. His subsequent work has focused on determining the properties, location and identity of the mechanically sensitive ion channels that transduce sound stimuli into electrical signals.[4]