Active control of sensory hair mechanics implied by susceptibility to media that induce contraction in muscle.

The motion of individual sensory hair bundles in the crista ampullaris was studied quantitatively by subjecting them to a brief jet of fluid in response to which they would swing away and then return by elasticity inherent at their insertion point. This motion was studied in media that would induce relaxation or contraction in a muscle system. The motion became severely restricted under conditions promoting contraction. Similar results were obtained by application to the organ of an ionophore that has the capacity to enter the cell membrane and allow influx of calcium ions. There was no effect of the ionophore in the absence of calcium ions. These results indicate that the sensory cells in the ear may possess a contractile machinery situated at the input end of the cell in the region of the sensory hairs and cuticular plate. The functional implication is that the mechanical input properties of the hair cells, and thus their excitability, can be under physiological control. It further implies that hair cells can produce a mechanical output in response to sensory or synaptic stimuli.