Different responses of mouse islets and MIN6 pseudo-islets to metabolic stimulation: a note of caution
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ORIGINAL ARTICLE
Different responses of mouse islets and MIN6 pseudo-islets to metabolic stimulation: a note of caution Torben Schulze1 • Mai Morsi1 • Dennis Bru¨ning1 • Kirstin Schumacher1 Ingo Rustenbeck1
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Received: 11 April 2015 / Accepted: 20 July 2015 Ó Springer Science+Business Media New York 2015
Abstract MIN6 cells and MIN6 pseudo-islets are popular surrogates for the use of primary beta cells and islets. Even though it is generally agreed that the stimulus-secretion coupling may deviate from that of beta cells or islets, direct comparisons are rare. The present side-by-side comparison of insulin secretion, cytosolic Ca2? concentration ([Ca2?]i) and oxygen consumption rate (OCR) points out where similarities and differences exist between MIN6 cells and normal mouse beta cells. In mouse islets and MIN6 pseudo-islets depolarization by 40 mM KCl was a more robust insulinotropic stimulus than 30 mM glucose. In MIN6 pseudo-islets, but not in mouse islets, the response to 30 mM glucose was much lower than to 40 mM KCl and could be suppressed by a preceding stimulation with 40 mM KCl. In MIN6 pseudo-islets, glucose was less effective to raise [Ca2?]i than in primary islets. In marked contrast to islets, the OCR response of MIN6 pseudo-islets to 30 mM glucose was smaller than to 40 mM KCl and was further diminished by a preceding stimulation with 40 mM KCl. The same pattern was observed when MIN6 pseudoislets were cultured in 5 mM glucose. As with insulin secretion memory effects on the OCR remained after washout of a stimulus. The differences between MIN6 cells and primary beta cells were generally larger in the responses to glucose than to depolarization by KCl. Thus, the use of MIN6 cells in investigations on metabolic signalling requires particular caution.
& Ingo Rustenbeck [email protected] 1
Institute of Pharmacology and Toxicology and Center of Pharmaceutical Engineering, University of Braunschweig, Mendelssohnstr. 1, 38106 Brunswick, Germany
Keywords Cytosolic calcium concentration Insulin secretion Oxygen consumption Pancreatic islets
Introduction Stimulation of insulin secretion by glucose and other nutrient secretagogues involves the metabolic breakdown of these stimuli [1, 2]. A decisive role of mitochondrial metabolism in this process was shown by microfluorimetry of autofluorescence and radioactive labelling of metabolites [3, 4]. The identification of the ATP-dependent K? channel (KATP channel) in the beta cell [5] provided the missing link between mitochondrial metabolism and the electrical activity [6], which triggers the exocytosis of the insulin granules [7, 8]. In well-coupled mitochondria, the generation of ATP by oxidative phosphorylation is reflected by the cellular oxygen consumption. Because of this, measurement of the oxygen consumption has been employed in earlier research to verify the nutrient-induced stimulation of mitochondrial ATP production [9, 10]. Later, the prominent role of the KATP channel and the cytosolic Ca2? concentration ([Ca2?]i) as acute regulators of
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