Active and passive behaviour in the regulation of stiffness of the lateral wall in outer hair cells of the guinea-pig

Abstract

The stiffness of the outer hair cell (OHC) lateral wall, measured by the micropipette aspiration technique, is non-linear, decreasing from the ciliary pole (stiffness parameter Sp 1.83+/-0.13 nN/microm n=10) towards the cell base (Sp 1.14+/-0.16 nN/microm, n=10) irrespective of the cochleoapical or cochleobasal origin of the cells. The length of the aspirated lateral wall segment was related exponentially to the duration of the applied negative pressure (6 cm H2O) in the synaptic region of the OHCs whereas an active, sigmoid component was observed between 30 and 60 s in the supranuclear regions. A significant increase of the midlateral wall stiffness (to 1.91+/-0.23 nN/microm; n=10) was observed in calcium-free medium and the sigmoid component of the response of the lateral wall was abolished. Salicylate (5 mM) had no significant effect on the active sigmoid behaviour of the lateral wall (n=10). Gadolinium (5 mM), a non-specific cation channel blocker, increased the stiffness of the lateral wall and attenuated the active component (n=10). The motor protein prestin thus does not seem to be involved in the active stiffness regulation seen in this study. A role for the cortical cytoskeleton in the regulation of stiffness seems reasonable according to our model. The mechanism may involve calcium-dependent metabolic modification of cytoskeletal or membrane proteins.

Slow motility, electromotility and lateral wall stiffness in the isolated outer hair cells

“…Stiffness of the lateral wall was measured by the glass micropipette aspiration technique during the slow shortening and recovery period (Brownell et al, 1985;Batta et al, 2003). Glass micropipettes were pulled from Clark EC15TF capillaries in five stages, the inner diameter was 2.8 ± 0.2 lm.…”

“…Pipettes were filled with HankÕs solution and connected to pressure application apparatus by a polyethylene tube. The aspiration pressure was 6 cm H 2 O and the aspirated lateral wall segments were videorecorded, digitized and analysed off-line after pseudocoloration (n = 5, in each experiment) (Batta et al, 2003).…”

“…Slow motile length changes (shortening) of isolated OHCs can be evoked by mechanical (perfusion of OHCsÕ in a bath) or chemical (K + ) challenges, osmotic effects, depolarization, elevation of the intracellular Ca 2+ concentration, [Ca 2+ ] i , or by tetanic electrical field stimulation (Dulon et al, 1988;Dulon and Schacht, 1992;Minamino et al, 1997;Batta et al, 2003;Farkas and Sziklai, 2003). Slow motile shortening of the OHCs is probably carried out by phosphorylation of the proteins in the actin-spectrin network of the cortical cytoskeleton in the lateral cell wall (Zenner et al, 1985;Slepecky, 1989) and require Ca 2+ (Zenner, 1986(Zenner, , 1988Dulon et al, 1988).…”

“…The effectiveness of these motor activities and hence the cochlear amplifier depends on the circumferential and axial stiffnesses of the OHCs (Tolomeo and Steele, 1995;Dallos et al, 1997;He et al, 2003). The characteristics of the lateral OHC wall stiffness as a primary variable in the whole cell global stiffness is related to the cell length (He et al, 2003;Batta et al, 2003).…”

Chlorpromazine Alters Cochlear Mechanics and Amplification: In Vivo Evidence for a Role of Stiffness Modulation in the Organ of Corti

“…OHC stiffness is largely dependent on the biophysical properties of the basolateral wall, which has a unique nanoscale organization of three layers: the plasma membrane, the cortical cytoskeleton, and the subsurface cisterna Dallos 1992). The static axial stiffness of isolated OHCs has been intensively investigated (e.g., Hallworth 1995; Holley and Ashmore 1988;Iwasa and Adachi 1997;Zenner et al 1992), and in vitro data have associated OHC stiffness with OHC electromotility (e.g., Batta et al 2003;Borko et al 2005;Chan et al 1998;Dallos et al 1997;Hallworth 1997;He and Dallos 1999;He et al 2003;Lue and Brownell 1999;Oghalai et al 2000;Russell and Schauz 1995). However, the in vivo role of OHC stiffness in electromotility and cochlear amplification in the intact organ of Corti (OoC) has remained unclear.…”