The islet of Langerhans plays a key role in glucose homeostasis through regulated secretion of the hormones insulin and glucagon. Islet research has focused on the insulin-secreting β-cells, even though aberrant glucagon secretion from α-cells also contributes to the aetiology of diabetes. Despite its importance, the mechanisms controlling glucagon secretion remain controversial. Proper α-cell function requires the islet milieu, where β- and δ-cells drive and constrain α-cell dynamics. The response of glucagon to glucose is similar between isolated islets and that measured in vivo, so it appears that the glucose dependence requires only islet-intrinsic factors and not input from blood flow or the nervous system. Elevated intracellular free Ca2+ is needed for α-cell exocytosis, but interpreting Ca2+ data is tricky since it is heterogeneous among α-cells at all physiological glucose levels. Total Ca2+ activity in α-cells increases slightly with glucose, so Ca2+may serve a permissive, rather than regulatory, role in glucagon secretion. On the other hand, cAMP is a more promising candidate for controlling glucagon secretion and is itself driven by paracrine signalling from β- and δ-cells. Another pathway, juxtacrine signalling through the α-cell EphA receptors, stimulated by β-cell ephrin ligands, leads to a tonic inhibition of glucagon secretion. We discuss potential combinations of Ca2+, cAMP, paracrine and juxtacrine factors in the regulation of glucagon secretion, focusing on recent data in the literature that might unify the field towards a quantitative understanding of α-cell function.

Original languageEnglish
Pages (from-to)127-136
Number of pages10
JournalDiabetes, Obesity and Metabolism
StatePublished - Sep 2018


  • EphA receptor
  • cAMP
  • calcium
  • cellular heterogeneity
  • ephrin
  • glucagon
  • insulin
  • islet of Langerhans
  • microscopy
  • somatostatin
  • α-cell


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