Two populations of pancreatic islet alpha-cells displaying distinct Ca2+ channel properties

Biochem Biophys Res Commun. 2006 Jun 23;345(1):340-4. doi: 10.1016/j.bbrc.2006.04.066. Epub 2006 Apr 25.


In low or absence of glucose, alpha-cells generate rhythmic action potentials and secrete glucagon. alpha-Cell T-type Ca(2+) channels are believed to be pacemaker channels, which are expected to open near the resting membrane potential (around -60 mV) to initiate a small depolarization. A previous publication, however, showed that alpha-cell T-type Ca(2+) channels have an activation threshold of -40 mV, which does not appear to fulfill their role as pacemakers. In this work, we investigated the Ca(2+) channel characteristics in alpha-cells of mouse-insulin-promoter green-fluorescent-protein (MIP-GFP) mouse. The beta-cells of MIP-GFP were conveniently distinguished as green cells, while immunostaining indicated that the majority of non-green cells were alpha-cells. We found that majority of alpha-cells possessed T-type Ca(2+) channels having an activation threshold of -40 mV; these cells also had high-voltage-activated (HVA) Ca(2+) channels (activation threshold of -20 mV). A novel finding here is that a minority of alpha-cells had T-type Ca(2+) channels with an activation threshold of -60 mV. This minor population of alpha-cells was, surprisingly, devoid of HVA Ca(2+) channels. We suggest that this alpha-cell subpopulation may act as pacemaker cells in low or absence of glucose.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology
  • Animals
  • Biological Clocks / physiology
  • Calcium / metabolism*
  • Calcium Channels / physiology*
  • Calcium Signaling / physiology*
  • Cells, Cultured
  • Glucagon-Secreting Cells / classification*
  • Glucagon-Secreting Cells / cytology
  • Glucagon-Secreting Cells / physiology*
  • Ion Channel Gating / physiology*
  • Membrane Potentials / physiology*
  • Mice


  • Calcium Channels
  • Calcium