Mechanoreceptors provide the inputs for the sensory modalities of touch, muscle tension, motion and hearing. This project is aimed at gaining insight into the process of mechano-sensory transduction at the molecular level. Methods are developed for the application of static and dynamic mechanical stress to planar lipid bilayers. Stress-strain relations are analyzed in these membranes with microsecond time resolution through voltage clamp measurements of the capacity currents. Applied stress patterns are steps, ramps and sinusoidal oscillations of different frequencies and amplitudes. Effects of lipid composition, solvent content and aqueous phase environment on the stress-strain relations are some of the parameters to be studied. Selected ion channels are incorporated into the bilayers. They include channels from lower organisms such as gramicidin, alamethicin or porin, as well as channels from higher organisms including sodium and potassium channels. Small membrane areas are isolated by a 30 Mu diameter patch pipette and changes of the channel gating kinetics, ion conductance and ion specificity in response to mechanical stress are investigated at the multi- and single channel level by current and voltage clamp. Mechanical sensitivity of the transduction is evaluated by determining the quantitative relations between stress-induced membrane strain and membrane conductance. The coupling between mechanical and inherent electrical oscillations is studied in membranes containing voltage-gated multichannel conductances. Channels from membranes of cochlear hair cells and stereocilia are inserted into lipid bilayers by fusion of membrane vesicles. The responses of these channels to mechanical stress are evaluated at the single- and multichannel level.
