MECHANOTRANSDUCTION IN VERTEBRATE HAIR-CELLS - STRUCTURE AND FUNCTIONOF THE STEREOCILIARY BUNDLE

The mechanosensitive hair cells of the vertebrate acousticolateralis s ystem have an apical bundle of stereocilia, deflections of which contr ol the opening of mechanoelectrical transduction channels and thus gen erate receptor potentials in the cell below. This review describes cur rent theories of hair cell function in the light of recent immunocytoc hemical and ultrastructural findings; in particular, the location and operation of the transduction channels are considered. The most widely accepted hypothesis of mechanotransduction by hair cells is that fine extracellular links that run between the tips of shorter stereocilia and the sides of taller ones operate the transduction channels. Howeve r, the fact that the transduction channels are amiloride sensitive has led to labeling experiments using antibodies to the amiloride-sensiti ve epithelial Nai channel from kidney which suggest that the mechanotr ansduction channels may not be directly associated with the tip links. Instead, they appear to be located near a junctionlike structure at t he point of contact between the shorter and taller stereocilia. The im plications of these findings for the tip link hypothesis are discussed .