Fig. 3.

Steady-state Ca²⁺ efflux from hair bundles and basolateral surfaces of isolated hair cells measured with a Ca²⁺-selective self-referencing electrode. The average background signals are indicated by dotted lines. A, Ca²⁺ efflux from hair bundles exceeded that from the basolateral membrane. By convention, Ca²⁺ efflux is illustrated as a negative voltage and Ca²⁺ influx as a positive voltage. During the course of the experiment the electrode was moved from a background region to the base of a hair bundle and then to the soma of that cell. B, Reduction of Ca²⁺ flux during electrode withdrawal from a hair cell. The measurement position of the electrode was moved to the indicated distances from a hair bundle; a gradient was detectable up to 50 μm away. The solid line represents the theoretical gradient calculated as described in the text. C, Ca²⁺ influx during transduction. While the extracellular Ca²⁺flux was measured near the top of the hair bundle, the bundle was deflected in the negative direction (start of record). Positive bundle displacements (indicated below the electrode signal) produced a net influx. D, Microinjection of vanadate into a hair cell reduced the steady-state Ca²⁺efflux from the hair bundle. The arrow indicates the time at which vanadate was injected. At the end of the experiment the electrode was withdrawn from the bundle to measure the background signal.