The design, calibration, and use of a water microjet for stimulating hair cell sensory hair bundles.

The design, calibration, and use of a noninvasive, noncontact device for stimulating hair cell hair bundles in vitro are described. This device employed a piezoelectric crystal, driven at high frequencies, to generate sinusoidal pressure in a contained fluid volume. The pressure was propagated to the tip of a glass micropipette and the oscillating water jet stimulus produced at the tip was used to stimulate sensory hair bundles. The movements of glass microbeads, caught in the oscillating pressure field of the water jet, provided a means of calibrating this stimulus. The linearity of the jet, its waveform and frequency response, the influence of pipette shape and tip diameter, as well as models to explain the operation of the water jet, are described. The use of this stimulus for measuring hair bundle micromechanics at high frequencies is then demonstrated.