An analysis of the hydraulic conductivity of the extracisternal spade of the cochlear outer hair cell

The cylindrically shaped cochlear outer hair cell (OHC) plays an important role in the transduction of acoustic energy into electrical energy in the c ochlea. The extracisternal space (ECiS) of the lateral wall of the OHC is t he fluid-filled space between the plasma membrane (PM) and the intracellula r subsurface cisterna (SSC). In the ECiS, an array of cylindrical micropill ars extends from the SSC to the PM. We obtain equations for the pressure, o smotic concentration and fluid velocity in the ECiS from the Brinkman-Stoke s equations for steady incompressible flow in a plane channel that encloses an array of cylinders and whose upper wall, i.e. the plasma membrane, has a hydraulic conductivity of P-PM. From these equations we obtain an estimat e for the hydraulic conductivity of the ECiS, P-ECiS. We show that the ECiS geometry accounts for PECiS being several orders of magnitude larger than P-PM and that P-ECiS increases with the width of the ECiS and decreases wit h the length of the ECiS.