The mechanisms of frequency tuning in gecko auditory hair cells.

We developed an isolated auditory papilla of the crested gecko to record from the hair cells and explore the origins of frequency tuning. Low-frequency cells displayed electrical tuning, dependent on Ca-activated K channels; high-frequency cells, overlain with sallets, showed a variation in hair bundle stiffness which when combined with sallet mass could provide a mechanical resonance of 1 to 6 kHz. Sinusoidal electrical currents injected extracellularly evoked hair bundle oscillations at twice the stimulation frequency, consistent with fast electromechanical responses from hair bundles of two opposing orientations, as occur in the sallets. Current evoked oscillations were reduced by lowering Ca, but not by block of the mechanotransduction channels by dihydrostreptomycin or salicylate block of prestin. We suggest the phenomenon may augment passive mechanical tuning of the sallets over the high-frequency region.