Figure 4. zprestin-transfected cells do not display somatic electromotility.

A, transfected HEK cells were probed for electromotility in a microchamber configuration, which allows simultaneous electrical stimulation and displacement recording. The rectangular slit indicates the area that was projected onto a photodiode for motility measurements. The stimulus command voltage (V_c) was applied between bath and microchamber compartment. Proportional to their degree of insertion into the microchamber, the cell's resultant membrane voltage swing was calculated to be ∼60% of V_c. B, lack of somatic motility in a zprestin-transfected HEK cell (upper trace). A 380 mV (peak-to-peak) voltage burst (lower trace) was applied via the microchamber. The voltage drop on the extruded segment was estimated to be 228 mV (peak-to-peak). The cell's resting membrane potentials normally were around −10 mV. Therefore, the effective membrane voltage was estimated to vary from −124 to +104 mV. Note that in contrast, robust electromotiltiy was observed in gprestin-transfected cells (middle trace). C, HEK cells transfected with zprestin display NLC confirming proper membrane targeting of zprestin in HEK cells. Voltage-dependent capacitance was measured using a 2-sine-wave method.