Red blood cell-mediated microinjection: methodological considerations.

Red blood cell-mediated microinjection is a powerful approach to introducing proteins into the cytoplasm of cultured cells. In the course of our microinjection studies of intracellular protein degradation, we have encountered several potential problems with certain proteins. The microinjection procedure may be accompanied by denaturation of protein by radiolabeling procedures, binding of protein to red cell ghosts during loading, degradation of protein by the red cell ghost prior to microinjection, and adsorption of protein that leaks from red cell ghosts in the presence of fusogen to the fibroblast monolayer. We conclude with a list of points that must be considered prior to use of red cell-mediated microinjection to study a particular protein.