A MEMBRANE MOTOR MODEL FOR THE FAST MOTILITY OF THE OUTER HAIR CELL

A model is presented for describing the membrane potential-dependent m otility of the outer hair cell. This model assumes that the motility i s due to conformational changes of motor molecules in the plasma membr ane. Two kinds of experimental observations, elasticity of the cell an d stretch dependence of the motor molecule, are important for characte rize this motility by the model. The motor molecule can be described b y a two-state model which has electrical and mechanical components in the free energy. The electrical component is due to the charge transfe rred across the membrane and the mechanical component is due to a chan ge in membrane area in the two states. It can be shown that the elasti c element and the motor element are connected in series. Thus the appa rent strain of the cell is represented by the sum of true elastic stra in and changes due to motor molecules, This model predicts the amplitu de of the movement and the force produced by the motility. The model p redicts the force produced under isometric condition is about 0.1 nN/m V, in agreement with values estimated from in vivo conditions. The eff ect of an elastic load attached to the cell is also discussed.