摘要Prestin is the motor protein of cochlear outer hair cells (OHCs). It is able to perform rapid and recipro-cal electromechanieal conversion that underlies OHC electromotility. Due to the inadequate size of a single prestin molecule to form the ～12 nm intramembraneous protein particles (IMPs) in the OHC lateral membrane (LM), the possibility of prestin oligomerization has been proposed. It has been suggested that prestin molecules form high-order oligomers, most likely as the tetramer, in heterologous systems. In OHCs, however, the oligomeric structure of prestin remains unelear. Here we calculated the prestin-related charge density in both gerbil and guinea pig OHCs through measuring their nonlinear capacitance (NLC) and LM surface area, showing that the average charge den-sity (22, 608 μm-2 in gerbils; 19, 460 μm-2 in guinea pigs) is statistically 4 times the average density of IMPs (5,686 μm-2 in gerbils; 5, 000 μm-2 in guinea pigs). This suggests that each IMP contains four prestin molecules based upon the notion that each prestin transfers a single elementary charge, implying that prestin forms tetramers in OHCs. To determine whether the prestin tetramer functions as a mechanical unit, we subsequently compared the slope factors (or) of electromotility and NLC simultaneously measured from the same OHC, showing that the α val-ues of the two are statistically the same. This suggests that each prestin molecule in the tetramer is mechanically independent and equally contributes to OHC electromotility.