Dihydrostreptomycin modifies adaptation and blocks the mechano-electric transducer in chick cochlear hair cells

Block of the mechano-electric transduction (MET) channel by dihydrostreptomycin (DHSM) and its effects on adaptation were investigated in dissociated cochlear hair cells of the chick with a whole-cell patch-electrode voltage clamp technique. DHSM reversibly blocked the MET channel in a dose- and voltage-dependent manner. At -50 mV, DHSM blocked the MET channel with a Hill coefficient of approximately 1 and a dissociation constant (Kd) of 2 x 10(-5) M. Rate constants for the DHSM to bind and to unbind to and from the channel were estimated, and could be larger than 5 x 10(7) M-1.s-1 and 1 x 10(3) s-1, respectively. The amplitude of MET current decreased during a constant displacement of the hair bundle. This current decay, the adaptation, disappeared in the DHSM medium. The disappearance and the emergence of adaptation did not have a simple relationship with the block of MET channel by DHSM, but appeared with some delay.