Effects of extracellular Ca2+ concentration on hair-bundle stiffness and gating-spring integrity in hair cells

AUTOR(ES)

Marquis, Robert E.

FONTE

The National Academy of Sciences of the USA

RESUMO

When a hair cell is stimulated by positive deflection of its hair bundle, increased tension in gating springs opens transduction channels, permitting cations to enter stereocilia and depolarize the cell. Ca2+ is thought to be required in mechanoelectrical transduction, for exposure of hair bundles to Ca2+ chelators eliminates responsiveness by disrupting tip links, filamentous interstereociliary connections that probably are the gating springs. Ca2+ also participates in adaptation to stimuli by controlling the activity of a molecular motor that sets gating-spring tension. Using a flexible glass fiber to measure hair-bundle stiffness, we investigated the effect of Ca2+ concentration on stiffness before and after the disruption of gating springs. The stiffness of intact hair bundles depended nonmonotonically on the extracellular Ca2+ concentration; the maximal stiffness of ≈1200 μN⋅m−1 occurred when bundles were bathed in solutions containing 250 μM Ca2+, approximately the concentration found in frog endolymph. For cells exposed to solutions with sufficient chelator capacity to reduce the Ca2+ concentration below ≈100 nM, hair-bundle stiffness fell to ≈200 μN⋅m−1 and no longer exhibited Ca2+-dependent changes. Because cells so treated lost mechanoelectrical transduction, we attribute the reduction in bundle stiffness to tip-link disruption. The results indicate that gating springs are not linearly elastic; instead, they stiffen with increased strain, which rises with adaptation-motor activity at the physiological extracellular Ca2+ concentration.

Documentos Relacionados

• A model for amplification of hair-bundle motion by cyclical binding of Ca2+ to mechanoelectrical-transduction channels
• Negative hair-bundle stiffness betrays a mechanism for mechanical amplification by the hair cell
• Hair-bundle movements elicited by transepithelial electrical stimulation of hair cells in the sacculus of the bullfrog
• Active hair-bundle movements can amplify a hair cell’s response to oscillatory mechanical stimuli
• Active hair-bundle motility harnesses noise to operate near an optimum of mechanosensitivity