VOLTAGE-MEDIATED CONFORMATIONAL-CHANGES OF A POLYELECTROLYTE IN A LINEAR ELASTIC MEMBRANE

The wall of the cylindrically-shaped outer hair cell is piezoelectric, which allows the cell to function as an electromechanical transducer in the mammalian inner ear. Polyelectrolytes, which are located in the cell wall, may be responsible for the cell's piezoelectric properties . The polyelectrolytes can change conformation in response to a change in the external electric field; this conformational change can cause the cell to change its length. We have developed a model to predict th e voltage response of a cylindrical cell whose wall contains conformat ionally-mobile polyelectrolytes. The cell wall is modeled as a rectang ular lattice of polyelectrolytes connected by springs. The springs rep resent the (non-piezoelectric) elastic portion of the cell wall. The p olyelectrolytes can exist in one of two possible conformations. The en ergy of the polyelectrolyte is a function of both the trans-wall elect ric potential difference and the forces which are applied by the surro unding elastic material in the wall. The fraction of polyelectrolytes in a given conformation is determined by the relative energies of the two conformations, by means of a Boltzmann distribution. If the electr ic potential difference and the pressure difference between the inside and outside of the cell are known, the model can predict the cell's r adius, the length, the fraction of polyelectrolytes in a given conform ation, and the electrical capacitance of the cell wall (due to the pol yelectrolyte activity). We also propose an experimental scheme which w ould provide data that could be used to evaluate the parameters in our model. Our simulations predict that the electrical capacitance vs, vo ltage function should exhibit a peak which simply shifts its location (without a significant change in height) when the intracellular pressu re is changed. In addition, we demonstrate that electrical stimulation of the cell, under conditions of constant cell volume, could result i n a significant change in the intracellular pressure.