Members of the VAMP family of synaptic vesicle proteins are components of glucose transporter-containing vesicles from rat adipocytes.

C.C Cain,W.S Trimble,G.E Lienhard

doi:10.1016/s0021-9258(19)49748-2

Abstract

Existing data support the hypothesis that insulin triggers the exocytosis of small vesicles containing the GluT4 isoform of the glucose transporter. The data also suggest that these vesicles reform through endocytosis of GluT4. These processes resemble those described for synaptic vesicles after depolarization of nerve cells. To determine whether GluT4 vesicles are related to synaptic vesicles, rat adipocyte low density microsomes (LDM), which are rich in GluT4 vesicles, were screened for the synaptic vesicle proteins synaptotagmin, synaptophysin, SV2, p29, rab3, and VAMP (synaptobrevin) by immunoblotting. Two polypeptides that reacted with antibodies against the VAMPs were identified, one with the same apparent size as the two isoforms of VAMP in the brain (18 kDa) and one that was slightly smaller (17 kDa). These members of the VAMP family were highly enriched in GluT4 vesicles isolated by immunoadsorption and translocated from the LDM to the plasma membrane in response to insulin. With the exception of rab3, which was observed in the LDM but was not localized in the GluT4 vesicles, the other synaptic vesicle proteins were not detected. The presence of the VAMPs in both GluT4 and synaptic vesicles suggests that the genesis and/or exocytosis of these two types of vesicles involve shared processes.

Highlights

Existing data support the hypothesis that insulin the cell surface, through endosomes, to vesicles which contriggers the exocytosis of small vesicles containing the tinue to fuse with the plasma membraneas long as insulin is
VAMP family were highly enriched in GluT4 vesicles found in endocrinecells, located in tubulovesicular structures isolated by immunoadsorption and translocated from that strikinglyresemble the LDM to the plasma membrane in response to insu- theGluT4-containing vesicles in morphology and cellular lin
The presence of the VAMPs in both GluT4 and synaptic vesicles suggests that the genesis and/or exocytosis of these two types of vesicles involvsehared processes

Summary

Introduction

Existing data support the hypothesis that insulin the cell surface, through endosomes, to vesicles which contriggers the exocytosis of small vesicles containing the tinue to fuse with the plasma membraneas long as insulin is. S. aureus cells loaded with antibody were added t o 1.3-ml samples a:: of the 48,000 X g supernatant (containing LDM from the adipocytes from one rat), and the mixturews ere incubated for 2 or 15h a t 4 "C.

Results

Conclusion