Helical structure of hair cell stereocilia tip links in the chinchilla cochlea

Outer-hair-cell stereocilia tip-link structure in the chinchilla cochlea wa s studied by transmission electron microscopy using tannic acid and Rutheni um red/Alcian blue histochemical procedures. Tannic acid and Ruthenium red/ Alcian blue treatments showed the tip link as a compact strand of filaments 9-12 nm thick. Fourier analysis of tip-link images showed that the strand is a three-start helical bundle of fine, coiled filaments which had an axia l period of 22.5 +/- 1.5 nm. Each of three coiled filaments in the strand s howed globular structures, 4.3 +/- 0.3 nm in diameter. The globular structu res may correspond to individual protein subunits or they may be repeating identical domains of one polypeptide. The three filaments of the helical ar ray may provide a rigidity to the tip link during stereocilia deflections. Alternatively, changes in the subunit or domain structure of each filament may result in a lengthening or shortening of the tip link strand.