An analysis of the hydraulic conductivity of the extracisternal space 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 cochlea. The extracisternal space (ECiS) of the lateral wall of the OHC is the fluid-filled space between the plasma membrane (PM) and the intracellular subsurface cisterna (SSC). In the ECiS, an array of cylindrical micropillars extends from the SSC to the PM. We obtain equations for the pressure, osmotic concentration and fluid velocity in the ECiS from the Brinkman-Stokes 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 estimate for the hydraulic conductivity of the ECiS, P _ECiS . We show that the ECiS geometry accounts for P _ECiS being several orders of magnitude larger than P _PM and that P _ECiS increases with the width of the ECiS and decreases with the length of the ECiS. Received: 6 January 1998 / Revised version: 12 October 1998