Chlorpromazine and force relaxation in the cochlear outer hair cell plasma membrane - An optical tweezers study

The cationic amphipath chlorpromazine (CPZ) is postulated to selectively partition into the inner leaflet of the plasma membranes and modulate the electromotile behavior of cochlear outer hair cells (OHCs). We used an optical tweezers system to characterize the mechanical properties of OHCs plasma membrane (PM) through the formation and analysis of membrane tethers in the presence and absence of CPZ. We observed characteristic force relaxation when the tethers were formed and maintained at a constant length for extended periods. This relaxation process was modeled using a 2(nd) order Kelvin body that provided stiffness, membrane viscosity-related measurements, and relaxation time constants, which collectively indicated an overall biphasic nature of relaxation. Our results with CPZ strengthen the hypothesis linking the drug's effect to reducing the mechanical interaction between PM and cytoskeleton.