Mechanisms of Control of the Free Ca2+ Concentration in the Endoplasmic Reticulum of Mouse Pancreatic β-Cells
Interplay With Cell Metabolism and [Ca2+]c and Role of SERCA2b and SERCA3
- Magalie A. Ravier1,2,
- Dorothée Daro1,
- Leticia Prates Roma1,
- Jean-Christophe Jonas1,
- Rui Cheng-Xue1,
- Frans C. Schuit3 and
- Patrick Gilon1⇓
- 1Pole d’Endocrinologie, Diabète, et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
- 2Institut de Génomique Fonctionnelle, CNRS UMR-5203, INSERM U661, Universités de Montpellier 1 et 2, Montpellier, France
- 3Gene Expression Unit, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
- Corresponding author: Patrick Gilon, .
M.A.R. and D.D. contributed equally to this work.
OBJECTIVE Sarco-endoplasmic reticulum Ca2+-ATPase 2b (SERCA2b) and SERCA3 pump Ca2+ in the endoplasmic reticulum (ER) of pancreatic β-cells. We studied their role in the control of the free ER Ca2+ concentration ([Ca2+]ER) and the role of SERCA3 in the control of insulin secretion and ER stress.
RESEARCH DESIGN AND METHODS β-Cell [Ca2+]ER of SERCA3+/+ and SERCA3−/− mice was monitored with an adenovirus encoding the low Ca2+-affinity sensor D4 addressed to the ER (D4ER) under the control of the insulin promoter. Free cytosolic Ca2+ concentration ([Ca2+]c) and [Ca2+]ER were simultaneously recorded. Insulin secretion and mRNA levels of ER stress genes were studied.
RESULTS Glucose elicited synchronized [Ca2+]ER and [Ca2+]c oscillations. [Ca2+]ER oscillations were smaller in SERCA3−/− than in SERCA3+/+ β-cells. Stimulating cell metabolism with various [glucose] in the presence of diazoxide induced a similar dose-dependent [Ca2+]ER rise in SERCA3+/+ and SERCA3−/− β-cells. In a Ca2+-free medium, glucose moderately raised [Ca2+]ER from a highly buffered cytosolic Ca2+ pool. Increasing [Ca2+]c with high [K] elicited a [Ca2+]ER rise that was larger but more transient in SERCA3+/+ than SERCA3−/− β-cells because of the activation of a Ca2+ release from the ER in SERCA3+/+ β-cells. Glucose-induced insulin release was larger in SERCA3−/− than SERCA3+/+ islets. SERCA3 ablation did not induce ER stress.
CONCLUSIONS [Ca2+]c and [Ca2+]ER oscillate in phase in response to glucose. Upon [Ca2+]c increase, Ca2+ is taken up by SERCA2b and SERCA3. Strong Ca2+ influx triggers a Ca2+ release from the ER that depends on SERCA3. SERCA3 deficiency neither impairs Ca2+ uptake by the ER upon cell metabolism acceleration and insulin release nor induces ER stress.
This article contains Supplementary Data online at http://diabetes.diabetesjournals.org/lookup/suppl/doi:10.2337/db10-1543/-/DC1.
- Received November 8, 2010.
- Accepted July 13, 2011.
- © 2011 by the American Diabetes Association.
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