In situ electrophysiological examination of pancreatic α cells in type 1 diabetes revealing the cellular basis of glucagon hypersecretion

Huang, Ya-Chi;Rupnik, Marjan S.;Herrera, Pedro L.;Gilon, Patrick;Gaisano, Herbert Y.
(2011) 47th EASD Annual Meeting of the European Association for the Study of Diabetes — Location: (Portugal) Lisbon (12.September.2011)

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  • Huang, Ya-Chi
    Author
  • Rupnik, Marjan S.
    Author
  • Herrera, Pedro L.
    Author
  • Gilon, Patrickorcid-logoUCLouvain
    Author
  • Gaisano, Herbert Y.
    Author
Abstract
Background and aims: The cellular properties of α cells in type 1 diabetes (T1D) are unknown. This is because T1D autoimmune destruction of β cells causes the islet mass to shrink in size rendering islet isolation and dispersion not technically feasible; and consequently electrophysiological characterization of islet cells to reveal the underling mechanisms explaining the distorted glucagon secretion in T1D could not be done. We employed GluCre-ROSA26-YFP (GYY) mice, which expresses YFP in pancreatic α cells. Along with our newly developed pancreas slice preparation whereby α cell and its precise secretory physiology within intact pancreatic tissue can be examined by patch clamp technique, unperturbed by conventional islet isolation and dispersion procedures, we are able to reliably localize and directly examine α cells electrophysiological properties in situ in health and T1D. We hypothesize that T1D α cells possess perturbed ion channels properties which contribute to hyperglucagonemia in early stage of T1D. Materials and methods: GYY mice were treated with streptozotocin (STZ) to induce T1D. IPGTT and radioimmunoassay (RIA) were performed to confirm diabetes phenotype. Pancreas slices were prepared from these mice to directly examine α cells ion channel properties in healthy and diseased islets by patch clamp technique. The identities of patched-cells were further confirmed by infusing fluoresecent marker (biocytin) during patching, showing its co-localization with YFP by confocal microscopy. Results: Normal GYY mice α cells in slices revealed identical electrophysiological features to those of their background C57/BL6 mice we previously characterized. These α cells are equipped with readily-activated A-type IK, voltage-gated INa, small size, low resting conductance, and inducible H/LVA ICa at -80mV. ICa influx correlated with glucagon exocytosis as either train of depolarization or UV photo-release of intracellular-loaded caged-Ca2+ stimulated Cm increase. 4 weeks after STZ treatment, GYY mice developed T1D, exhibiting higher fasting glucose, slower glucose clearance after a glucose challenge and higher fasting (control; 89 pg/ml vs. STZ group;122 pg/ml) and fed (control; 78 pg/ml vs. STZ group;112 pg/ml) serum glucagon levels. α cells in slices from these diabetic mice revealed augmentation of INa (control; 368 ± 43 pA vs. STZ group; 480 ± 71pA) and LVA ICa amplitudes (control; 40 ± 5 vs. STZ group; 49 ± 6 pA). HVA ICa however remained unaltered by T1D (control; 44 ± 5 pA vs. STZ group; 46 ± 6 pA) . Voltage-gated K+ current was found to be increased (STZ group; 2.13 nA vs. control; 1.76 nA). α cell size was unchanged compared to control (control; 4.7 ± 0.20 pF vs. STZ group; 4.8 ± 0.23 pF). Conclusion: GYY mouse α cell ion channel properties examined in slices were largely consistent with our previous findings and others, validating the feasibility of using pancreas slice approach to investigate α cells in normal and diabetic subjects. We postulate that the observed upregulation of INa and LVA ICa in diabetic α cells potentially elevates membrane potential that would more readily to trigger HVA Ca2+ channels opening, with ensuing initiation of action potential firing leading to glucagon secretion. This explains in part the observed glucagon hypersecretion in early stage of T1D
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Huang, Y.-C., Rupnik, M. S., Herrera, P. L., Gilon, P., & Gaisano, H. Y. (2011). In situ electrophysiological examination of pancreatic α cells in type 1 diabetes revealing the cellular basis of glucagon hypersecretion. Diabetologia : clinical and experimental diabetes and metabolism, 54(Suppl. 1), S260-S261. https://doi.org/10.1007/s00125-011-2276-4 (Original work published 2011)