Polarized transport of C6-NBD–SM depends on the
degree of cell polarity. The SAC was loaded with C6-NBD–SM as
described in MATERIALS AND METHODS. Transport of the lipid analogue
from the SAC was then monitored for 20 min in back exchange medium. In
(A), the percentage of C6-NBD-SM–labeled BCP was determined in 18-
(□) and 72-h-old (░⃞) cell cultures. The asterisk marks the
statistically significant (Student's t test, p <
0.05) decrease in BCP labeling in 72-h-old cell cultures, when compared
with the 18-h-old cell cultures. In (B) and (C), the distribution of
the lipid analogue within the labeled BCP of 18- and 72-h-old cell
cultures, respectively, was analyzed: the compartmental distribution of
the lipid is shown before (□) and after ░⃞ a 20-min chase from the
SAC. *Statistically significant differences (Student's
t test, p < 0.05) between the corresponding BCP
compartments (BC, SAC, and BC+SAC) in (B) and (C).