title: Two populations of pancreatic islet alpha-cells displaying distinct Ca2+ channel properties.
abstract: 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.
authors: Department of Medicine, University of Toronto, Toronto, Canada M5S 1A8. ymleung@mail.cmu.edu.tw
authors: Yuk M
authors: YM
authors: Leung
authors: Ishtiaq
authors: I
authors: Ahmed
authors: Laura
authors: L
authors: Sheu
authors: Robert G
authors: RG
authors: Tsushima
authors: Nicholas E
authors: NE
authors: Diamant
authors: Herbert Y
authors: HY
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