Electrophysiological characterization of pancreatic islet cells in the mouse insulin promoter-green fluorescent protein mouse.
We recently reported a transgenic [mouse insulin promoter (MIP)-green fluorescent protein (GFP)] mouse in which GFP expression is targeted to the pancreatic islet beta-cells to enable convenient identification of beta-cells as green cells. The GFP-expressing beta-cells of the MIP-GFP mouse were functionally indistinguishable from beta-cells of normal mice. Here we characterized the ionic channel properties and exocytosis of MIP-GFP mouse islet beta- and alpha-cells. Beta-cells displayed delayed rectifying K+ and high-voltage-activated Ca2+ channels and exhibited Na+ currents only at hyperpolarized holding potential. Alpha-cells were nongreen and had both A-type and delayed rectifier K+ channels, both low-voltage-activated and high-voltage-activated Ca2+ channels, and displayed Na+ currents readily at -70 mV holding potential. Alpha-cells had ATP-sensitive K+ channel (KATP) channel density as high as that in beta-cells, and, surprisingly, alpha-cell KATP channels were more sensitive to ATP inhibition (IC50=0.16+/-0.03 mM) than beta-cell KATP channels (IC50=0.86+/-0.10 mM). Whereas alpha-cells were rather uniform in size [2-4.5 picofarad (pF)], beta-cells varied vastly in size (2-12 pF). Of note, small beta-cells (<4.5 pF) showed little exocytosis, whereas medium beta-cells (5-8 pF) exhibited vigorous exocytosis, but large beta-cells (>8 pF) had weaker exocytosis. We found no correlation between beta-cell size and their Ca2+ channel density, suggesting that Ca2+ influx may not be the cause of the heterogeneity in exocytotic responses. The MIP-GFP mouse therefore offers potential to further explore the functional heterogeneity in beta-cells of different sizes. The MIP-GFP mouse islet is therefore a reliable model to efficiently examine alpha-cell and beta-cell physiology and should greatly facilitate examination of their pathophysiology when the MIP-GFP mice are crossed with diabetic models.
Leung
Yuk M
YM
Department of Medicine, Room 7308, or Dr. Herbert Y. Gaisano, Room 7226, Medical Sciences Building, 1 King's College Circle, University of Toronto, Toronto, Ontario M5S 1A8, Canada. yukman.leung@utoronto.ca
Ahmed
Ishtiaq
I
Sheu
Laura
L
Tsushima
Robert G
RG
Diamant
Nicholas E
NE
Hara
Manami
M
Gaisano
Herbert Y
HY
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D004594:Electrophysiology; D005089:Exocytosis; D049452:Green Fluorescent Proteins / Q000235:genetics*; D066298:In Vitro Techniques; D007328:Insulin / Q000235:genetics*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic / Q000502:physiology*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology; D011401:Promoter Regions, Genetic; D015222:Sodium Channels / Q000502:physiology
D015220:Calcium Channels; D007328:Insulin; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015222:Sodium Channels; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate