Intracellular ATP-sensitive K+ channels in mouse pancreatic beta cells: against a role in organelle cation homeostasis

2006 | journal article; research paper. A publication with affiliation to the University of Göttingen.

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​Intracellular ATP-sensitive K+ channels in mouse pancreatic beta cells: against a role in organelle cation homeostasis​
Varadi, A.; Grant, A.; McCormack, M.; Nicolson, T.; Magistri, M.; Mitchell, K. J. & Halestrap, A. P. et al.​ (2006) 
Diabetologia49(7) pp. 1567​-1577​.​ DOI: https://doi.org/10.1007/s00125-006-0257-9 

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Authors
Varadi, A.; Grant, A.; McCormack, M.; Nicolson, T.; Magistri, M.; Mitchell, K. J.; Halestrap, A. P.; Yuan, H.; Schwappach, B. ; Rutter, G. A.
Abstract
Aims/hypothesis: ATP-sensitive K+ (K-ATP) channels located on the beta cell plasma membrane play a critical role in regulating insulin secretion and are targets for the sulfonylurea class of antihyperglycaemic drugs. Recent reports suggest that these channels may also reside on insulin-containing dense-core vesicles and mitochondria. The aim of this study was to explore these possibilities and to test the hypothesis that vesicle-resident channels play a role in the control of organellar Ca2+ concentration or pH. Methods: To quantify the subcellular distribution of the pore-forming subunit Kir6.2 and the sulfonylurea binding subunit SUR1 in isolated mouse islets and clonal pancreatic MIN6 beta cells, we used four complementary techniques: immunoelectron microscopy, density gradient fractionation, vesicle immunopurification and fluorescence-activated vesicle isolation. Intravesicular and mitochondrial concentrations of free Ca2+ supercript stop were measured in intact or digitonin-permeabilised MIN6 cells using recombinant, targeted aequorins, and intravesicular pH was measured with the recombinant fluorescent probe pHluorin. Results: SUR1 and Kir6.2 immunoreactivity were concentrated on dense-core vesicles and on vesicles plus the endoplasmic reticulum/Golgi network, respectively, in both islets and MIN6 cells. Reactivity to neither subunit was detected on mitochondria. Glibenclamide, tolbutamide and diazoxide all failed to affect Ca2+ uptake into mitochondria, and K-ATP channel regulators had no significant effect on intravesicular free Ca2+ concentrations or vesicular pH. Conclusions/Interpretation: A significant proportion of Kir6.2 and SUR1 subunits reside on insulin-secretory vesicles and the distal secretory pathway in mouse beta cells but do not influence intravesicular ion homeostasis. We propose that dense-core vesicles may serve instead as sorting stations for the delivery of channels to the plasma membrane.
Issue Date
2006
Journal
Diabetologia 
ISSN
0012-186X
Language
English

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