Outer Hair Cell Receptor Current and its Effect on Cochlear Mechanics

In 1948 Gold suggested that the vibration of the organ of Corti relied on active mechanical feedback to maintain its sensitivity and frequency selectivity. Since then mathematical models of its labile vibration (Khanna and Leonard, 1982; Sellick et al, 1982, 1983, 1984; Robles et al, 1986) agree with Gold’s view that forces must be applied to the organ to partially cancel the inherent viscous forces (Neely and Kim, 1983, 1986; de Boer, 1983). This force generation process within the cochlea has been termed the active process, while the forces themselves have been termed negative damping. More recently, it has been observed that isolated outer hair cells (OHCs) from the mammal contract in vitro in response to applied electric current (Brownell et al, 1983, 1985; Ashmore, 1987). These and other observations (see Patuzzi and Robertson, 1988) suggest that the OHCs are the negative damping elements in cochlear mechanics, and that their synchronous contraction is controlled by the AC receptor current that flows through them, or by voltages that these currents produce. This combination of mechano-electric (ME) transduction at the apex of the hair cells (Holton and Hudspeth, 1987) and electromechanical (EM) cellular contraction has been termed “bi-directional transduction” (Weiss, 1982).