Fig. 1. Expression and localization of InsP₃R-3 during the polarization of MDCK cells. MDCK cells, plated at 10⁴ cells/cm² were cultured over a period of 12 days. (A) Western blot: 50 µg of protein of cell lysates, corresponding to 1.2-1.4x10⁵ cells from cultures of 3, 6 and 10 days, were loaded on each lane; the last lane was loaded, as a positive control, with a sample of HeLa cell lysate. Proteins were subjected to 5% (w/v) SDS-PAGE and the western blotting was carried out using a primary antibody directed against the type 3 InsP₃R. (B) TER. (C) Localization of InsP₃R-3 and proteins of the endoplasmic reticulum (ER) in MDCK cells cultured for 3, 6 and 10 days; in each case the corresponding phase contrast images are shown on the left. (D) Localization of another marker of the endoplasmic reticulum, the protein PDI, in cultures of 3 and 10 days, with the corresponding phase contrast image on the left. Bar, 10 µm.