|
||
J. Cell Biol.,
Volume 139, Number 4, November 17, 1997 907-916
Department of Neurology and Department of Physiology, Programs in Neuroscience and Cell Biology, University of California
at San Francisco School of Medicine, San Francisco, California 94143
Previous studies have indicated that neuro-endocrine cells store monoamines and acetylcholine
(ACh) in different secretory vesicles, suggesting that
the transport proteins responsible for packaging these
neurotransmitters sort to distinct vesicular compartments. Molecular cloning has recently demonstrated
that the vesicular transporters for monoamines and
ACh show strong sequence similarity, and studies of
the vesicular monoamine transporters (VMATs) indicate preferential localization to large dense core vesicles (LDCVs) rather than synaptic-like microvesicles
(SLMVs) in rat pheochromocytoma PC12 cells. We
now report the localization of the closely related vesicular ACh transporter (VAChT). In PC12 cells, VAChT
differs from the VMATs by immunofluorescence and
fractionates almost exclusively to SLMVs and endosomes by equilibrium sedimentation. Immunoisolation further demonstrates colocalization with synaptophysin
on SLMVs as well as other compartments. However,
small amounts of VAChT also occur on LDCVs. Thus,
VAChT differs in localization from the VMATs, which
sort predominantly to LDCVs. In addition, we demonstrate ACh transport activity in stable PC12 transformants overexpressing VAChT. Since previous work has
suggested that VAChT expression confers little if any
transport activity in non-neural cells, we also determined its localization in transfected CHO fibroblasts.
In CHO cells, VAChT localizes to the same endosomal compartment as the VMATs by immunofluorescence,
density gradient fractionation, and immunoisolation
with an antibody to the transferrin receptor. We have
also detected ACh transport activity in the transfected
CHO cells, indicating that localization to SLMVs is not
required for function. In summary, VAChT differs in
localization from the VMATs in PC12 cells but not
CHO cells.
This article has been cited by other articles:
|
|