Morphological localisation of sulfonylurea receptor 1 in endocrine cells of human, mouse and rat pancreas

Abstract

Aims/hypothesis Sulfonylurea receptor 1 (SUR1) is the regulatory subunit of ATP-sensitive K channels in beta cells. Morphological methods (immunohistochemistry and sulfonylurea binding) were used to establish the cellular and subcellular location of SUR1 in human and rodent islets. Results In the human, mouse and rat pancreas, all endocrine cells of the islets were immunolabelled with an anti-SUR1 antibody, whereas tissues containing SUR2 were consistently negative, as were those from Sur1 (also known as Abcc8) −/− mice. In beta cells of the three species, the plasma membrane was distinctly stained, but SUR1 was mainly present over the cytoplasm, with an intensity that varied between cells. Electron microscopy showed that SUR1 was immunolocalised in insulin, glucagon and somatostatin granules. In rat beta cells degranulated by in vivo treatment with glibenclamide (known as glyburide in the USA and Canada), the insulin and SUR1 staining intensity was similarly decreased by ∼45%, whereas SUR1 staining was not changed in non-beta cells. In all islet cells, binding of glibenclamide labelled with fluorescent dipyrromethane boron difluoride (BODIPY-FL) was punctate over the cytoplasm, compatible with the labelling of endocrine granules. A faint labelling persisted in Sur1 −/− mice, but it was not different from that obtained with BODIPY-FL alone used as negative control. Conclusions/interpretation Our study immunolocalised SUR1 in alpha, beta and delta cells of human, mouse and rat islets, and for the first time visualised it in the plasma membrane. We also show that SUR1 is abundant in endocrine granules, where its function remains to be established. No specific sulfonylurea-binding sites other than SUR1 are identified in islet cells by the glibenclamide-BODIPY-FL technique.

Glucose Acutely Decreases pH of Secretory Granules in Mouse Pancreatic Islets

“…It has been suggested that Cl influx into granules occurs through ClC-3 channels regulated by a sulfonylurea receptor-like protein (16). Although SUR1 is present in the insulin granule membrane (44,45), it is not involved in the acidification by glucose since the phenomenon was unaltered in islets from Sur1 knock-out mice (Fig. 5I) (46) or stimulation of the phospholipase C-protein kinase C pathway by activating muscarinic receptors with 10 M acetylcholine (47) had no effect on granular pH in low glucose and did not affect the acidification by 15 mM glucose (data not shown).…”

Endoplasmic reticulum accumulation of Kir6.2 without activation of ER stress response in islet cells from adult Sur1 knockout mice

“…Shyng, University of California, USA), which was detected by the EnVision peroxidase complex (1 h; Dako, Carpintera, USA) and by 3,3′-diaminobenzidine (DAB; brown deposit; Guiot et al 2007). For electron microscopy, after the removal of Epon with sodium metaperiodate (Merck, Darmstadt, Germany) and pretreatment with 0.1% trypsin/0.1% CaCl 2 (Sigma-Aldrich, Steinheim, Germany) in phosphate-buffered saline (PBS) for 20 min at 37°C, semi-thin (1 µm thick) or ultra-thin (75 nm) pancreas sections were incubated overnight at 4°C with rabbit anti-Kir6.2 (1/20) or with goat anti-calreticulin (1/100; Santa Cruz, Calif., USA).…”

“…The results were expressed as the number of particles per micrometer L-RER length or per insulin granule (modified from Guiot et al 2007).…”

Impact of Sur1 gene inactivation on the morphology of mouse pancreatic endocrine tissue

“…For histology and immunochemistry, sections were either stained with haematoxylin-eosin or immunolabelled for insulin, pro-insulin and SUR1 peptides as described by Guiot et al (2007).…”

“…They play a key role in the control of insulin secretion by linking the electrical membrane activity to the cellular metabolic rate (Dunne et al 1997;Ashcroft and Gribble 1998;Henquin 2000). The presence of functional K-ATP channels (Göpel et al 2000;Gromada et al 2004;MacDonald et al 2007) or their molecular subunits (Bokvist et al 1999;Guiot et al 2007) has also been found in other islet cells secreting glucagon (α) and somatostatin (δ).…”