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. 1999 Dec;10(12):4163–4176. doi: 10.1091/mbc.10.12.4163

Figure 3.

Figure 3

EEs are not connected to the plasma membrane (PM). (A–C) Ultrathin Epon sections of PC12 cells fixed at 15°C in the presence of the membrane-impermeable reagent ruthenium red (electron-dense staining) to mark all plasma membrane-associated structures. (D and E) Ultrathin cryosections of PC12 cells immunogold labeled for rab4 (D) or clathrin (E). (A) Ruthenium red staining was clearly visible at the PM and constricted clathrin-coated pits (CCP). (B and C) By contrast, EEs were consistently negative for ruthenium red. (D) The small GTPase rab4 (10-nm gold) is found on EE vacuoles and associated tubules and vesicles (arrowheads) but absent from the PM. (E) The electron-dense coating of EE vacuole contains clathrin (10-nm gold). M, mitochondrion; sg, secretory granule. Bars, 100 nm.