Electrical Control of the Transduction Channels' Gating Force in Mechanosensory Hair Cells

The inner ear's hair cells rely on mechanosensitive ion channels to convert vibrations of their hair bundles into electrical signals. The mechanical correlates of channel gating-the gating force and the gating swing-are fundamental determinants of hair-cell mechanosensitivity but are still poorly understood. Here we show that varying the electrical potential across the sensory hair-cell epithelium continuously modulates the gating force, by up to ±100%. Our observations also revealed an abrupt transition between states of weak and strong gating force at a threshold potential, so that strong gating forces associated to high mechanosensitivity are observed only when the calcium influx through the channels is large enough, but not too large. Gating-force changes, remarkably enough, were explained by the modulability of the gating swing, ranging from values comparable to the channel pore size to nearly tenfold larger. Gating-swing control is expected to underly the hair cell's ability to tune its mechanosensitivity to minute sound stimuli.