A gamma-aminobutyric acid transporter driven by a proton pump is present in synaptic-like microvesicles of pancreatic beta cells.
A variety of peptide-secreting endocrine cells contain a population of recycling microvesicles that share several major membrane polypeptides with neuronal synaptic vesicles (SVs). The function of these synaptic-like microvesicles (SLMVs) remains to be elucidated. It was previously suggested that SLMVs of pancreatic beta cells may store and secrete gamma-aminobutyric acid (GABA). GABA, the major nonpeptide inhibitory neurotransmitter of the central nervous system, is stored in and secreted from SVs. GABA uptake into SVs is mediated by a transporter that is driven by a vacuolar proton ATPase. GABA is also present at high concentration in the endocrine pancreas where it is selectively localized in insulin-secreting beta cells, the core cells of pancreatic islets. GABA is not present in peripheral islet cells (mantle cells), represented primarily by glucagon-secreting alpha cells. In this study, an immunoisolation procedure was used to purify SLMVs from cell lines derived from mouse beta cells and alpha cells. SLMVs obtained from the beta-cell line, but not those obtained from the alpha-cell line, displayed a GABA-transport activity dependent upon a proton electrochemical gradient generated by a vacuolar proton ATPase. These data support the hypotheses that (i) SLMVs have a secretory function similar to that of SVs and (ii) beta-cell SLMVs are involved in the secretion of GABA, which in turn may have a paracrine function on mantle cells of the islet.
Thomas-Reetz
A
A
Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510.
Hell
J W
JW
During
M J
MJ
Walch-Solimena
C
C
Jahn
R
R
De Camilli
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002458:Cell Fractionation; D002460:Cell Line; D005033:Ethylmaleimide / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D050485:GABA Plasma Membrane Transport Proteins; D005968:Glutamate Decarboxylase / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007515:Islets of Langerhans / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins / Q000032:analysis; D009840:Oligomycins / Q000494:pharmacology; D015388:Organelles / Q000378:metabolism* / Q000648:ultrastructure; D027361:Organic Anion Transporters; D017494:Proton Pumps / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D050683:R-SNARE Proteins; D013572:Synaptic Vesicles; D016708:Synaptophysin / Q000032:analysis; D014638:Vanadates / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009840:Oligomycins; D027361:Organic Anion Transporters; D017494:Proton Pumps; D050683:R-SNARE Proteins; D016708:Synaptophysin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D014638:Vanadates; D005680:gamma-Aminobutyric Acid; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases; D005968:Glutamate Decarboxylase; D005033:Ethylmaleimide