Fig. 4. Immunoelectron microscopy analysis. InsP₃R-3 was immunostained (6 nm gold particles, arrows) in ultrathin cryosections of polarized MDCK cells. Panel A shows a section passing through the different junctions present along the contact zone between two adjacent cells. The image shown in the inset B is centered on the upper part of the cells, at the limit between the apical pole and the lateral one. InsP₃R-3 labeling was nearly exclusively seen in the vicinity of the tight junction (TJ). AJ, adherens junction; DS, desmosome; ap, apical surface; mv, microvilli. Bar, 100 nm.