Glucose-dependent docking and SNARE protein-mediated exocytosis in mouse pancreatic alpha-cell

• The function of alpha-cells in patients with type 2 diabetes is often disturbed; glucagon secretion is increased at hyperglycaemia, yet fails to respond to hypoglycaemia. A crucial mechanism behind the fine-tuned release of glucagon relies in the exocytotic machinery including SNARE proteins. Here, we aimed to investigate the temporal role of syntaxin 1A and SNAP-25 in mouse alpha-cell exocytosis. First, we used confocal imaging to investigate glucose dependency in the localisation of SNAP-25 and syntaxin 1A. SNAP-25 was mainly distributed in the plasma membrane at 2.8 mM glucose, whereas the syntaxin 1A distribution in the plasma membrane, as compared to the cytosolic fraction, was highest at 8.3 mM glucose. Furthermore, following inclusion of an antibody against SNAP-25 or syntaxin 1A, exocytosis evoked by a train of ten depolarisations and measured as an increase in membrane capacitance was reduced by ~50%. Closer inspection revealed a reduction in the refilling of granules from the reserve pool (RP), but also showed a decreased size of the readily releasable pool (RRP) by ~45%. Disparate from the situation in pancreatic beta-cells, the voltage-dependent Ca²⁺ current was not reduced, but the Ca²⁺ sensitivity of exocytosis decreased by the antibody against syntaxin 1A. Finally, ultrastructural analysis revealed that the number of docked granules was >2-fold higher at 16.7 mM than at 1 mM glucose. We conclude that syntaxin 1A and SNAP-25 are necessary for alpha-cell exocytosis and regulate fusion of granules belonging to both the RRP and RP without affecting the Ca²⁺ current.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Annan klinisk medicin (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Other Clinical Medicine (hsv//eng)

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Endokrinologi och diabetes (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Endocrinology and Diabetes (hsv//eng)

Nyckelord

Islet

Alpha-cell

Exocytosis

Glucose dependence

Syntaxin 1A

SNAP-25

TEM

Capacitance measurements

Animals

Cytoplasmic Granules

Exocytosis

Glucagon

Glucagon-Secreting Cells

Glucose

Mice

SNARE Proteins

Synaptosomal-Associated Protein 25

Syntaxin 1

Publikations- och innehållstyp

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