Electromotility in outer hair cells: a supporting role for fast potassium conductance.

Motility of outer hair cells underlies the cochlear amplifier, which is critical for the ear's sensitivity and fine tuning. Of the two motile mechanisms present in these cells, electromotility at the lateral wall depends on the receptor potential and thus depends on currents through the cell body. We found that, in the guinea pig cochlea, basal turn outer hair cells have a fast-activating ion current (tau < 0.3 ms at 23 degrees C), which is absent in apical turn cells. This finding is consistent with our previous theoretical analysis that a fast-activating potassium current is required only in the basal turn to counteract the capacitive current and thereby to enhance the effectiveness of electromotility. Thus, our finding is consistent with the functional significance of electromotility. We conjecture therefore that the current reduces the capacitance of the outer hair cell in order to increase hearing bandwidth.