Abstract
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.