Lipid bilayer membranes are soft condensed matter systems with physico-chemical properties that are important in a variety of cell functions. The mechanical properties of membranes are now fairly well understood; however less attention has been paid to the electrical properties of membranes and the potential biological role of electromechanical coupling. A unique cell found in the mammalian cochlea, the outer hair cell, possesses an apparent membrane-based form of electromechanical coupling mediated by a newly discovered protein named prestin. Recently, optical tweezer experiments revealed that the force required to maintain the length of tethers formed from the surface of outer hair cells is highly sensitive to the transmembrane potential. Interestingly, epithelial cells also display similar behavior, although at a reduced magnitude. We will present thermodynamic models that consider the effects of various forms of electromechanical coupling on tether behavior. The experimental data is consistent with electrically-induced membrane bending (flexoelectricity), which we have previously proposed as a mechanism for outer hair cell electromotility. Understanding how prestin endows membranes with these piezoelectric-like properties requires characterizing the organization of prestin in the membrane. We currently use advanced optical imaging techniques (FRET and FRAP) to characterize the mobility of prestin in the membrane and to assess its potential for oligomerization. These data present evidence for self-association of prestin molecules, which could provide a mechanism for electrically induced curvature changes. Modulation of membrane electromechanics is of potential physiological relevance, and we will show evidence that salicylate (an active metabolite of aspirin) and solution pH alter the mechanical properties and dipole potential of giant unilamellar vesicles. Thus, in both cells and pure membranes, there appears to be coupling between electrical and mechanical energy, supporting the new paradigm of the membrane as an electromechanical structure.
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