Selective anchoring in the specific plasma membrane domain: a role in epithelial cell polarity

These results were semi-quantitated by digital video analysis of fluorescent semi-thin frozen sections, as previously described (82) , to avoid the bias introduced by nonlinearity in photographic reproduction. The gain of the video camera was fixed so that the values of the plasma membrane pixels from unextracted and extracted samples fell, for each antigen, within the linear range of sensitivity of the camera. Significant peaks of basal (incorrect domain) fluorescence were found with the A1 marker ( Fig. 4 A, arrows) in randomly taken fluorescence profiles from nonextracted cells; these peaks were abolished in TX-100-extracted monolayers (Fig. 4 B, arrows) . Likewise, basolateral antigens showed some apical fluorescence observed as apical peaks of fluorescence (Fig. 4 , C and E, black arrows). After detergent extraction these peaks of fluorescence in the incorrect domain decreased to a greater extent than the peaks in the "correct" domain ( Fig. 4, D and F, black arrows) .