Two components of transducer adaptation in auditory hair cells.
Mechanoelectrical transducer currents in turtle auditory hair cells adapted to maintained stimuli via a Ca(2+)-dependent mechanism characterized by two time constants of approximately 1 and 15 ms. The time course of adaptation slowed as the stimulus intensity was raised because of an increased prominence of the second component. The fast component of adaptation had a similar time constant for both positive and negative displacements and was unaffected by the myosin ATPase inhibitors, vanadate and butanedione monoxime. Adaptation was modeled by a scheme in which Ca(2+) ions, entering through open transducer channels, bind at two intracellular sites to trigger independent processes leading to channel closure. It was assumed that the second site activates a modulator with 10-fold slower kinetics than the first site. The model was implemented by computing Ca(2+) diffusion within a single stereocilium, incorporating intracellular calcium buffers and extrusion via a plasma membrane CaATPase. The theoretical results reproduced several features of the experimental responses, including sensitivity to the concentration of external Ca(2+) and intracellular calcium buffer and a dependence on the onset speed of the stimulus. The model also generated damped oscillatory transducer responses at a frequency dependent on the rate constant for the fast adaptive process. The properties of fast adaptation make it unlikely to be mediated by a myosin motor, and we suggest that it may result from Ca(2+) binding to the transducer channel or a nearby cytoskeletal element.
Wu
Y C
YC
Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
Ricci
A J
AJ
Fettiplace
R
R
D000222:Adaptation, Physiological; D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D009218:Myosins / Q000037:antagonists & inhibitors; D009991:Oscillometry; D018408:Patch-Clamp Techniques; D011930:Reaction Time / Q000502:physiology; D014426:Turtles; D014638:Vanadates / Q000494:pharmacology
D004791:Enzyme Inhibitors; C004717:diacetylmonoxime; D014638:Vanadates; D004533:Egtazic Acid; D009218:Myosins; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D003931:Diacetyl; D002118:Calcium