Biophysical Properties of Mechanotransduction

Abstract

In early time, the coarse signals, such as cochlear microphonics and summating potentials, were recorded by electrocochleography by placing a metal electrode on the round window, which reflected the sound-induced electrical responses mostly mediated by hair cells. However, these signals are mainly a summated response from a group of hair cells. The direct evidence came from the intracellular recording of hair cells in the tail lateral line of mudpuppy Necturus maculosus (Harris et al., Science 167(3914):76–79, 1970). Similarly, auditory response from the cochlear hair cells was probed by intracellular recording in guinea pig (Russell and Sellick, Nature 267(5614):858–860, 1977; J Physiol 284:261–290, 1978). In isolated bullfrog saccule tissue, the mechanotransduction (MET) current was recorded in hair cells, which provided the first evidence that the deflection of hair bundle induced receptor potential change of hair cells (Hudspeth and Corey, Proc Natl Acad Sci USA 74(6):2407–2411, 1977). Nevertheless, whole-cell patch clamp was applied to hair cells to achieve a detailed information of the MET channel including some single-channel behaviour (Ohmori, J Physiol 359:189–217, 1985). From then on, researchers have studied most of the biophysical properties of the channel systematically by electrophysiology, pharmacology, and optical imaging without knowing the molecular identity of the MET channel. Now several important questions have been tackled in this chapter, including the following: Where does the channels localize in the hair cells? What kind of ions do the channels pass through? How are the channels activated and then adapted? How many channels are there opened per tip link? What are the single-channel properties?