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K J Parker, P M Jones, C H Hunton, S J Persaud, C G Taylor, and S L Howell

ABSTRACT

The liberation of arachidonic acid (AA), by phospholipase A2 (PLA2), is the rate-limiting step in a number of cell signalling pathways. In the pancreatic β-cell, AA itself is thought to participate in the regulation of insulin secretion. Recently a Ca2+-sensitive, AA-selective cytosolic PLA2 (type IV cPLA2) has been isolated from the human monocyte U937 cell line. Although the DNA sequence of this enzyme implies a molecular weight of 85 kDa, the protein migrates with a molecular weight of 100-110 kDa on SDS-PAGE. In many cell types, cPLA2s which are reactive towards antibodies raised against the type IV cPLA2 have been shown to hydrolyse AA from membrane glycerophospholipids. Using a polyclonal antibody raised against a recombinant form of type IV cPLA2, we have detected an immunoreactive protein with a molecular weight of 93·5 kDa in rat islets of Langerhans. Furthermore, we have detected similar immunoreactive proteins in insulin-secreting β-cell lines and have shown co-expression of type IV cPLA2 immunoreactivity and insulin immunoreactivity in rat pancreatic β-cells. Under non-stimulatory conditions the 93·5 kDa immunoreactive protein detected in rat islets of Langerhans was located predominantly in the cytosolic fraction. We have shown that immunoprecipitation of the rat immunoreactive protein from rat islet homogenates significantly decreases the total dithiothreitol/β-mercaptoethanol-insensitive PLA2 activity by 56·4±7% This provides further evidence that the immunoreactive rat protein is a type IV cPLA2 and is responsible for a large component of the PLA2 activity in rat islets of Langerhans. It is possible that, in the rat β-cell, type IV cPLA2 couples the increase in intracellular Ca2+, brought about by insulin secretagogues, to the liberation of AA and the subsequent release of insulin.

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Yu-Feng Zhao, Damien J Keating, Maria Hernandez, Dan Dan Feng, Yulong Zhu, and Chen Chen

Introduction Normal glucose homeostasis requires finely controlled orchestration of insulin secretion in response to subtle changes in blood glucose levels. Glucose-induced insulin secretion occurs when pancreatic β-cells utilize

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Riccarda Granata, Marco Volante, Fabio Settanni, Carlotta Gauna, Corrado Ghé, Marta Annunziata, Barbara Deidda, Iacopo Gesmundo, Thierry Abribat, Aart-Jan van der Lely, Giampiero Muccioli, Ezio Ghigo, and Mauro Papotti

peptides stimulated glucose-induced insulin secretion by β-cells ( Granata et al . 2007 ). However, data regarding ghrelin influence on insulin secretion are still contradictory; both inhibitory and stimulatory effects having been reported ( Date et al

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Haihua Yang and Linghai Yang

, are regulated by glucose and hormones. cAMP/PKA in pancreatic islets β cell A hallmark of T2D is an early defect in glucose-stimulated insulin secretion from pancreatic β cells ( Nolan et al . 2011 ). Following a meal, glucose

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Yang Mi, Na Guo, Tongqiang He, Jing Ji, Zhibin Li, and Pu Huang

lactate dehydrogenase A (LDHA). LDHA is usually kept in low expression level in insulin-secreting β-cells ( Sekine et al . 1994 ), and its overexpression affects glucose-induced insulin secretion ( Ainscow et al . 2000 ). We then transduced miR-410 into

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Hongjie Zhang, Jing Li, Xiangying Liang, Yun Luo, Ke Zen, and Chen-Yu Zhang

the gut lumen might underlie this L-cell response. It is known that one mechanism for sensing glucose in pancreatic endocrine β-cells is uncoupling protein 2 (UCP2)-mediated insulin secretion. UCP2 is a member of the inner mitochondrial membrane anion

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S Dubois, A M Madec, A Mesnier, M Armanet, K Chikh, T Berney, and Ch Thivolet

analyzed by IRMA to evaluate insulin secretion. Insulin secretion studies were performed using comparable islet numbers. Aliquots of supernatants were stored at −20 °C until insulin concentrations were measured by a highly specific IRMA (BI-insulin IRMA

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Pierre Moulin, Yves Guiot, Jean-Christophe Jonas, Jacques Rahier, Olivier Devuyst, and Jean-Claude Henquin

Introduction Pancreatic β cells adjust insulin secretion to the ambient concentration of glucose and other nutrients through changes in their metabolism ( Newgard 2002 , MacDonald et al. 2005 a , Matschinsky et al. 2006

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Jenny Vikman, Xiaosong Ma, Gregory H Hockerman, Patrik Rorsman, and Lena Eliasson

, Nagamatsu et al. 1999 ) and in insulin-secreting cell lines ( Jacobsson et al. 1994 , Martin et al. 1995 , Oho et al. 1995 , Wheeler et al. 1996 ). The requirement for syntaxin 1 in insulin secretion has previously been demonstrated by inclusion

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Horng-Yih Ou, Hung-Tsung Wu, Feng-Hwa Lu, Yu-Chu Su, Hao-Chang Hung, Jin-Shang Wu, Yi-Ching Yang, Chao-Liang Wu, and Chih-Jen Chang

physiological functions contribute to insulin secretion ( Itoh et al . 2003 ). Activation of FFAR1 increases phospholipase C (PLC) activity through the Gq protein to facilitate insulin secretion ( Feng et al . 2006 ). In addition, results from recent studies