We recently showed that in Caco-2 cells the high affinity Na+-/Dglucose
cotransporter (SGLTl) resides in intracellular endosomes
which are attached to microtubules and therefore proposed that
the activity of SGLTl is regulated by intracellular trafficking
(Kipp et al., 2003). To visualize the dynamics of the transporter,
we expressed a GFP-SGLT1 fusion in COS-7 cells. Using
fluorescence microscopy, we discovered the GFP-SGLT1 protein
in vesicular stmctures resembling those of endogenous SGLTl in
Caco-2 cells. We were able to show the SGLT1-containing
vesicles moving rapidly within COS-7 cells transiently expressing
GFP-SGLT1 by means of time-lapse fluorescence microscopy.
This movement was completely abolished by the disruption of the
microtubule network with nocodazole. Next, we compared the
features of the SGLTl vesicles and vesicles containing the
transferrin receptor (TR). Therefore we incubated COS-7 cells
expressing GFP-SGLT1 with Alexa Fluor 546-transferrin to
compare the localization and the trafficking of SGLTl and the
TR. Fluorescence microscopy of these specimens revealed a
localization of the TR in vesicular structures that do not
colocalize with SGLT1-vesicles and move with a higher speed.
Our presented results confirm a vesicular localization of SGLTl
and display the microtubule-dependent transport of these vesicles
in hing cells. The mechanism of SGLTl endo-/exocytosis is
clearly distinguishable from the transport of the transferrin recepto