EXPERIMENTAL FIGURE 11-24 The oocyte expression assay is useful in comparing the function of normal and mutant forms of a channel protein. An oocyte from the follicle of a frog is first treated with collagenase to remove the surrounding follicle cells, leaving a denuded oocyte, which is then microinjected with mRNA encoding the channel protein under study. See T. P. Smith, 1988, Trends Neurosci. 11:250.