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

• Published in: Biochemical and biophysical research communications Vol. 345; no. 1; pp. 340 - 344
• Main Authors: Leung, Yuk M, Ahmed, Ishtiaq, Sheu, Laura, Tsushima, Robert G, Diamant, Nicholas E, Gaisano, Herbert Y
• Format: Journal Article
• Language: English
• Published: United States 23.06.2006
• Subjects: 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
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2006.04.066

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.