Cryosectioning of epithelial cells grown on permeable supports

Epithelial cells cultured on permeable supports, with nutrient access to the basal cell surface, reach a high degree of differentiation and polarity. Furthermore, cells grown on polycarbonate filters can be readily cross-sectioned for light microscopy. Localization of antigens to the apical or basolateral regions or surfaces of the cell may be accomplished by direct or indirect immunofluorescence techniques performed on frozen sections. We show here by indirect immunofluorescence the localization of apical and basolateral antigens and the tight junction protein ZO-1 on Madin-Darby canine kidney cells grown on Millicell PCF filters and sectioned to 0.5 µm with an ultracryomicrotome. We also show simple methods for obtaining 4-µm cryostat sections of T84 cells grown on Transwell filters, and illustrate by direct fluorescence the internalization of cholera toxin in these cells.