Electrically evoked motions of the isolated mouse tectorial membrane

Abstract

We discovered motion during application of AC voltage (0.8 V peak amplitude, f=1 kHz) on the surface of the isolated mouse tectorial membrane (TM). The TM's motion response, which contained an average peak amplitude of 4 nm (in 5 TM preparations) was measured using a novel atomic force sensing (AFS) technique (Rousso et al, 1997). A 2-D lateral mapping of motion at several points on the TM surface shows that the TM expands near the negative electrode and contracts near the positive electrode with a stationary pivot point between the two electrodes. Lowering the pH in the bath surrounding the TM from 7.3 to 4.07 decreased the maximum amplitude of displacement from 4 nm to approximately 2.5 nm while lowering the bath pH from 4.07 to 3.96 caused the TM to undergo a [pi] phase shift in its motion response. Based on this data, the TM has an isoelectric point and pKa near pH 4.011. This supports the model that the TM motion response is altered by the state of ionization of charge groups in the TM, which varies with bath pH.