Fig. 3. Immunogold electron microscopy of ASIP/PAR-3 (A-D) and ZO-1 (C,D) in epithelial cells of distal (A,C) and proximal (B,D) renal tubules. Ultrathin cryosections of rat renal tubular epithelial cells were labeled with anti-ASIP/PAR-3 pAb (A,B; 5 nm gold particles). In both the distal (A) and proximal (B) tubules, gold particles for ASIP/PAR-3 are concentrated exclusively in the cytoplasm of TJ. Gold particles are constantly observed at the apical edge of TJ, and are also frequently found at the basal edge of TJ. (C,D) Double immunolabeling of renal tubular epithelium for ASIP/PAR-3 and ZO-1. In contrast to ASIP/PAR-3 (10 nm gold particles), ZO-1 (5 nm gold particles) distributes alongside TJ in the distal (C) and proximal (D) tubules. Apical is up and basal is down in these figures (A-D). TJ, tight junction. Bars, 100 nm.