The outer hair cell motor in membrane patches

We have used patch-clamp techniques to record the charge movement associated with motility in patches of basolateral membrane from isolated outer hair cells. Charge movement has been measured from the voltage-dependent capacitance. Using 3 to 4 Momega pipettes with tip diameters of 3 micron the measured maximum voltage-dependent capacitance was 56 +/- 6 fF at -36 mV when the resting membrane potential was -20 mV. The calculated total charge movement was 5.6 +/- 0.6 fC (n = 13) and the inferred density of univalent motor elements was 8400/micron2. Negative pressure (applied via the pipette) increased membrane tension and shifted the capacitance peak to depolarised potentials. Under conditions of isotropic membrane stress there was no change in the peak measured capacitance in contrast to that measured in previous whole-cell recordings.