Relationship between stiffness,internal cell pressure and shape of outer hair cells isolated from the guinea-pig hearing organ

The mechanical properties of outer hair cells are of importance for normal hearing, and it has been shown that damage of the cells can lead to a reduction in the hearing sensitivity. In this study, we measured the stiffness of isolated outer hair cells in hyper- and hypotonic conditions, and examined the change in stiffness in relation to the corresponding changes in internal cell pressure and cell shape. The results showed that the axial stiffness of isolated outer hair cells (30–90 μm in length, 8–12 μm in diameter), ranging from 0.13–5.39 mN m^?1, was inversely related to cell length. Exposure to hyper- and hypotonic external media with a small percentage change in osmolality caused a similar magnitude of change in cell length and cell diameter, but an average 60% change in cell stiffness. Therefore, a moderate osmotic change in the external medium can lead to a significant alteration in cell stiffness. The findings thus indicate an important contribution of internal cell pressure to cell stiffness.