High resolution measurement of membrane receptor endocytosis.

We present a new approach to quantify the half-life of membrane proteins on the cell surface, through tagging the protein with the photoconvertible fluorescent protein, Dendra2. Upon exposure to 405 nm light, Dendra2 is photoconverted from green to red emission. Total internal reflection fluorescence microscopy (TIRF) is applied to limit visualization of fluorescence to proteins located on the plasma membrane. Conversion of Dendra2 works as a pulse chase experiment through monitoring only the population of protein that has been photoconverted. As the protein is endocytosed the red emission decreases due to the protein leaving the TIRF field of view. This method is not impacted by the insertion of new protein into the plasma membrane as newly synthesized protein only exhibits green emission. We used this approach to determine the half-life of ENaC on the plasma membrane illustrating the high temporal resolution capability of this technique compared to current methods.