Membrane Cholesterol Strongly Influences Confined Diffusion of Prestin

Prestin is the membrane motor protein that drives outer hair cell (OHC) electromotility, a process that is essential for mammalian hearing. Prestin function is sensitive to membrane cholesterol levels, and numerous studies have suggested that prestin localizes in cholesterol-rich membrane microdomains. Previously, fluorescence recovery after photobleaching experiments were performed in HEK cells expressing prestin-GFP after cholesterol manipulations, and revealed evidence of transient confinement. To further characterize this apparent confined diffusion of prestin, we conjugated prestin to a photostable fluorophore (tetramethylrhodamine) and performed single-molecule fluorescence microscopy. Using single-particle tracking, we determined the microscopic diffusion coefficient from the full time course of the mean-squared deviation. Our results indicate that prestin undergoes diffusion in confinement regions, and that depletion of membrane cholesterol increases confinement size and decreases confinement strength. By interpreting the data in terms of a mathematical model of hop-diffusion, we quantified these cholesterol-induced changes in membrane organization. A complementary analysis of the distribution of squared displacements confirmed that cholesterol depletion reduces prestin confinement. These findings support the hypothesis that prestin function is intimately linked to membrane organization, and further promote a regulatory role for cholesterol in OHC and auditory function

Moisture movement in soils on the Hanford Reservation

Methods being studied are as follows: the thermodynamic method based on water potential and thermocouple psychrometers; the tracer method using atmospheric tritium; the annual water balance based on the annual heat balance; the field lysimeter using thermocouple psychrometers; the influence of soil breathing as a result of changes in barometric pressure; and the influence of soil stratification. Progress to date has involved the installation of thermocouple psychrometers from the surface to the water table 310 feet below. These instruments are in the process of equilibration. Isothermal methods of analyzing water potential must be extended to include nonisothermal conditions which are dominant at the Hanford Reservation. Tracer techniques using tritium analyses of soil samples have successfully demonstrated that archaic water exists in virgin soil at the Hanford Reservation from a depth of approximately 7 meters to the water table, indicating that percolation has been limited to lesser depths. The annual heat balance indicates that quantities of water many times greater than the annual average precipitation of 16 centimeters can be evaporated from the soils at the Hanford Reservation during a normal summer. This indicates that the critical precipitation (P/sub c/) value may be greater than 30 to 50 centimeters of water. More precise values of the Bowen's ratio for the Hanford Reservation are required to refine this computation. The field lysimeter is perhaps the most direct method of determining the critical precipitation values for the Hanford Reservation but as yet has not been used. (auth