Similar experiments were done to see if 1 lMONO inhibited export
from the central ERC. In control cells incubated in MEM alone
for 10 min followed by continuous uptake of Tf-FITC for 45 min, Tf
and LDLR were located in peripheral SEs throughout the cytoplasm
(Fig. 3A and B). However, when cells were pre-treated with 1 lM
ONO for 10 min followed by continuous uptake of Tf-FITC for
45 min, Tf and LDLR accumulated in the centrally located ERC
(Fig. 3C and D). This accumulation was reversible because following
washout of ONO and chase for 20 min, Tf was recycled from
the central compartment into the media and lost from cells
(Fig. 3E). In addition, LDLRs were once again found in peripheral
compartments indicating that they too had recycled to the cell surface
for another round of endocytic uptake (Fig. 3H). In contrast,
cells treated identically but then chased in 1 lM ONO showed that
Tf and LDLR were retained in the central ERC (Fig. 3G and H). These
results show that 1 lM ONO allows transport of both Tf and LDLR
to, but not export from, the centrally located ERC.