Outer Hair Cells Possess Acetylcholine Receptors and Produce Motile Responses in the Organ of Corti

Abstract

Active mechanical processes in the mammalian cochlea are considered to be new general mechanisms in hearing that differ from the classical description of the passive travelling wave of the basilar membrane. Located in outer hair cells (OHCs) they are thought to contribute to sensitivity and frequency selectivity or to control the basilar membrane (BM) location and the operating point of the stereocilia. Reversible slow (Zenner et al., 1985; Zenner, 1986) and fast (Brownell et al., 1985; Zenner et al., 1987; Ashmore, 1987) active longitudinal movements of the cylindrical body of isolated OHCs that have been demonstrated in vitro support this notion. Furthermore, we could show, that the cuticular plate (CP) of OHCs is capable of slow and fast motile responses that displace the stereociliary bundle (Zenner, 1986, 1988; Zenner et al., 1988). Biochemical analyses revealed that an interaction of actin and myosin is the molecular basis of Ca²⁺/ATP-dependend slow motile responses of OHCs (Zenner, 1988). A direct extrapolation, however, from these in vitro results to the conditions in the organ of Corti (OC) is rather dubious. Furthermore, the control mechanisms of OHC motility have not been finally elucidated. Control could be achieved e.g. by the efferent nerves as well as by a.c. and d.c. mo dulations of the OHC membrane potential.