High frequency force generation in outer hair cells from the mammalian ear

Mammalian outer hair cells generate mechanical forces at acoustic frequencies and can thus amplify the sound stimulus within the inner ear. The mechanism of force generation depends upon the plasma membrane potential but not upon either calcium or ATP. Forces are generated in the lateral cortex along the full length of the cell. The cortex includes a two-dimensional cytoskeletal lattice composed of circumferential filaments 6-7 nm thick that are cross-linked by filaments 3-4 nm thick and 40-60 nm long. The two filament types may, respectively, be actin and some form of spectrin. The lattice reinforces the cylindrical shape of the cell and permits limited changes in length. Beneath it lie the lateral cisternae, a regular system of multi-layered membranes. Force-generation may depend upon voltage-dependent shape changes in proteins that lie either in the plasma membrane or in the cytoskeletal lattice.