Abstract
The outer hair cell is thought to enhance the sensitivity of mammalian hearing. Its lateral wall consists of 3 concentric layers: an outermost plasma membrane, a cortical lattice, and an innermost collection of flattened membranes called the subsurface cisternae. The cytoplasm requires positive pressure for full expression of the outer hair cell's electromotility. Using micropipette aspiration, we investigated the mechanics of the guinea pig's outer hair cell lateral wall at room temperature (22°C) and at the guinea pig's body temperature (39°C). Although there was a 10% decrease in stiffness parameter with an increase from room to body temperature, the difference was not statistically significant; values ranged from 0.45 to 0.65 dyne/cm. With sufficient negative pressure, the cytoplasmic membrane is separated from the rest of the outer hair cell's lateral wall, a process that leads to vesiculation of the plasma membrane. Vesiculation occurs at a lower pressure than at body temperature. Our results demonstrate that the stiffness parameter of the outer hair cell lateral wall at body temperature is similar to that at room temperature. However, the plasma membrane's attachment to the cortical lattice is greatly altered by temperature. The decrease in strength of membrane attachment at body temperature may result from a change in membrane fluidity, making it more easy for membrane attachment sites to break free and permit vesiculation. Whether the tethering of the plasma membrane to the cortical lattice is lost under clinically pathologic conditions deserves future study.
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