The membrane protein SLC26A5 (prestin) contracts in the plane of the membrane in response to depolarization of the cell caused by opening of the mechanoelectric transduction (MET) channel (inferred from rat homologs). Likewise, SLC26A5 expands in the plane of the membrane in response to hyperpolarization caused by MET channel closing. A current model for the reaction posits that the association of anions (chloride or bicarbonate) with a binding pocket midway along the permeation pathway within SLC26A5 causes a change in the area occupied by SLC26A5 in the membrane (inferred from the rat homolog). An influx of cations through the MET channel causes dissociation of anions from SLC26A5, reversing the conformational change. The contraction-elongation cycle of OHCs, due to conformational changes of prestin, provides feedback-amplification of the motions (principally the reticular lamina) of the organ of Corti. At low sound levels the amplification is about a 1000-fold, decreasing nonlinearly as sound level increases. In the absence of either OHCs (Ryan and Dallos 1975) or functional prestin (inferred from mouse homologs) the amplification disappears.