Loss of coupling between calcium influx, energy consumption and insulin secretion associated with development of hyperglycaemia in the UCD-T2DM rat model of type 2 diabetes |
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Authors: | A M Rountree B J Reed B P Cummings S-R Jung K L Stanhope J L Graham S C Griffen R L Hull P J Havel I R Sweet |
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Institution: | 1. Diabetes and Obesity Center of Excellence, University of Washington, 850 Republican Street, Seattle, WA, 98109-8055, USA 2. Department of Molecular Biosciences, School of Veterinary Medicine and Department of Nutrition, University of California, Davis, CA, USA 3. Bristol-Myers Squibb, Princeton, NJ, USA 4. Department of Medicine, VA Puget Sound Health Care System and University of Washington, Seattle, WA, USA
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Abstract: | Aims/hypothesis Previous studies on isolated islets have demonstrated tight coupling between calcium (Ca2+) influx and oxygen consumption rate (OCR) that is correlated with insulin secretion rate (ISR). To explain these observations, we have proposed a mechanism whereby the activation of a highly energetic process (Ca2+/metabolic coupling process CMCP]) by Ca2+ mediates the stimulation of ISR. The aim of the study was to test whether impairment of the CMCP could play a role in the development of type 2 diabetes. Methods Glucose- and Ca2+-mediated changes in OCR and ISR in isolated islets were compared with the time course of changes of plasma insulin concentrations observed during the progression to hyperglycaemia in a rat model of type-2 diabetes (the University of California at Davis type 2 diabetes mellitus UCD-T2DM] rat). Islets were isolated from UCD-T2DM rats before, 1 week, and 3 weeks after the onset of hyperglycaemia. Results Glucose stimulation of cytosolic Ca2+ and OCR was similar for islets harvested before and 1 week after the onset of hyperglycaemia. In contrast, a loss of decrement in islet OCR and ISR in response to Ca2+ channel blockade coincided with decreased fasting plasma insulin concentrations observed in rats 3 weeks after the onset of hyperglycaemia. Conclusions/interpretation These results suggest that phenotypic impairment of diabetic islets in the UCD-T2DM rat is downstream of Ca2+ influx and involves unregulated stimulation of the CMCP. The continuously elevated levels of CMCP induced by chronic hyperglycaemia in these islets may mediate the loss of islet function. |
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