Positive Feedback Amplifies the Response of Mitochondrial Membrane Potential to Glucose Concentration in Clonal Pancreatic Beta Cells

Analysis of the cellular mechanisms of metabolic disorders, including type 2 diabetes mellitus, is complicated by the large number of reactions and interactions in metabolic networks. Metabolic control analysis with appropriate modularization is a powerful method for simplifying and analyzing these networks. To analyze control of cellular energy metabolism in adherent cell cultures of the INS-1 832/13 pancreatic beta-cell model we adapted our microscopy assay of absolute mitochondrial membrane potential (Delta psi M) to a fluorescence microplate reader format, and applied it in conjunction with cell respirometry. In these cells the sensitive response of Delta psi M to extracellular glucose concentration drives glucose-stimulated insulin secretion. Using metabolic control analysis we identified the control properties that generate this sensitive response. Force-flux relationships between Delta psi M and respiration were used to calculate kinetic responses to Delta psi M of processes both upstream (glucose oxidation) and downstream (proton leak and ATP turnover) of Delta psi M The analysis revealed that glucose-evoked Delta psi M hyperpolarization is amplified by increased glucose oxidation activity caused by factors downstream of At high glucose, the hyperpolarized Delta psi M is stabilized almost completely by the action of glucose oxidation, whereas proton leak also contributes to the homeostatic control of Delta psi M at low glucose. These findings suggest a strong positive feedback loop in the regulation of beta-cell energetics, and a possible regulatory role of proton leak in the fasting state. Analysis of islet bioenergetics from published cases of type 2 diabetes suggests that disruption of this feedback can explain the damaged bioenergetic response of beta-cells to glucose. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases-edited by P. Hemachandra Reddy. (C) 2016 Elsevier B.V. All rights reserved.