Cochlear potential difference between endolymph fluid and the hair cell’s interior: a retold interpretation based on the Goldman equation

摘要

Reported cochlear potential values of near 150 mV are often attributedto endolymph itself, although membrane potentials resultfrom ion fluxes across the adjacent semipermeable membranesdue to concentration gradients. Since any two fluids separated by asemipermeable membrane develop potential due to differences insolute concentrations, a proposed interpretation here is that positivepotential emanates from the Reissner membrane due to smallinflux of sodium from perilymph to endolymph. Basolateral haircell membranes leak potassium into the interstitial fluid and thisnegative potential inside hair cells further augments the electricgradient of cochlear potential. Taken together as a sum, these twopotentials are near the reported values of cochlear potential. This isbased on reported data for cochlear fluids used for the calculationof Nernst and Goldman potentials. The reported positive potentialof Reissner membrane can be explained almost entirely by thetraffic of Na+ that enters endolymph through this membrane. Atthe apical membrane of hair cells, acoustic stimulation modulatesstereocillia permeability to potassium. Potassium concentrationgradients on the apical membrane are low (the calculated Nernstvalue is <+3 mV), suggesting that the potassium current is not causedby the local potassium concentration gradient, but an electricfield between the positive sodium generated potential on the Reissnermembrane and negative inside hair cells. Potassium is forcedby this overall electric field to enter hair cells when stereociliaare permeable due to mechanical bending