Cited by 209Pancreatic function and diabetesCellular transport and secretionIon channel regulation and function

Tight coupling between electrical activity and exocytosis in mouse glucagon-secreting alpha-cells.

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Barg, S, Galvanovskis, J, Göpel, S O, Rorsman, P, Eliasson, L·2000·Diabetes

Abstract

alpha-Cells were identified in preparations of dispersed mouse islets by immunofluorescence microscopy. A high fraction of alpha-cells correlated with a small cell size measured as the average cell diameter (10 microm) and whole-cell capacitance (<4 pF). The alpha-cells generated action potentials at a low frequency (1 Hz) in the absence of glucose. These action potentials were reversibly inhibited by elevation of the glucose concentration to 20 mmol/l. The action potentials originated from a membrane potential more negative than -50 mV, had a maximal upstroke velocity of 5 V/s, and peaked at +1 mV. Voltage-clamp experiments revealed the ionic conductances underlying the generation of action potentials. alpha-Cells are equipped with a delayed tetraethyl-ammonium-blockable outward current (activating at voltages above -20 mV), a large tetrodotoxin-sensitive Na+ current (above -30 mV; peak current 200 pA at +10 mV), and a small Ca2+ current (above -50 mV; peak current 30 pA at +10 mV). The latter flowed through omega-conotoxin GVIA (25%)- and nifedipine-sensitive (50%) Ca(2+)-channels. Mouse alpha-cells contained, on average, 7,300 granules, which undergo Ca(2+)-induced exocytosis when the alpha-cell is depolarized. Three functional subsets of granules were identified, and the size of the immediately releasable pool was estimated as 80 granules, or 1% of the total granule number. The maximal rate of exocytosis (1.5 pF/s) was observed 21 ms after the onset of the voltage-clamp depolarization, which is precisely the duration of Ca(2+)-influx during an action potential. Our results suggest that the secretory machinery of the alpha-cell is optimized for maximal efficiency in the use of Ca2+ for exocytosis.

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Crossref · 10.2337/diabetes.49.9.1500

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  • The small store-operated current is sufficient to trigger voltage-dependent Ca2+ influx because of the high input resistance and the fact that action potentials start at voltages as negative as -60 mV.

    “The small store-operated current is sufficient to trigger voltagedependent Ca 2+ influx because of the high input resistance [12] and the fact that the action potentials start at voltages as negative as -60 mV [13,39,43].”
  • Mouse alpha-cells show little KATP channel expression, corresponding to 2% of that in mouse beta-cells.

    “mouse ␣-cells show little K ATP channel expression (25,26), corresponding to 2% of that in mouse ␤-cells (27).”
  • Glucose hyperpolarizes mouse alpha-cells and lowers [Ca2+]i.

    “the sugar hyperpolarizes mouse ␣-cells (14,27,29) and, as now confirmed, lowers [Ca 2ϩ ] i (14).”

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Authors
Barg, S., Galvanovskis, J., Göpel, S. O., Rorsman, P., & Eliasson, L.
Affiliations
Lund University (SE)
Venue
Diabetes
Published
2000-09-01
Volume
49
Issue
9
Pages
1500-1510
ISSN
  • 0012-1797 (ISSN-L)
  • 1939-327X
OpenAlex
W2163595098
Cited by
209
References
30
Citations by year
2026: 6 · 2025: 6 · 2024: 2 · 2023: 6 · 2022: 7 · 2021: 11 · 2020: 12 · 2019: 4 · 2018: 2 · 2017: 4 · 2016: 9 · 2015: 3 · 2014: 10 · 2013: 10 · 2012: 12
FWCI
3.55
Type
journal article
Language
en
Open access
Locations
  • Diabetes (publishedVersion)
  • PubMed (publishedVersion)
  • Lund University Publications (Lund University) (submittedVersion)
Funders
  • Fondation pour la Recherche Médicale
  • Knut och Alice Wallenbergs Stiftelse
  • Novo Nordisk
  • Direktör Albert Påhlssons Stiftelse
  • Magnus Bergvalls Stiftelse
  • Medical Research Council
Topics
  • Health Sciences › Medicine › Surgery › Pancreatic function and diabetes
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Cellular transport and secretion
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Ion channel regulation and function
Keywords
alpha cells, glucagon secretion, exocytosis, action potential, calcium channels, calcium-induced exocytosis, secretory granules, pancreatic islets, sodium current, tetrodotoxin-sensitive sodium current, omega-conotoxin GVIA, secretory machinery
MeSH terms
Animals, Cells, Cultured, Cytoplasmic Granules, Diazoxide, Exocytosis, Glucagon, Islets of Langerhans, Membrane Potentials, Mice, Inbred Strains, Tetrodotoxin, Tolbutamide, Sodium Channels, Mice

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