Sustainability transition pathways in the building sector: Energy-efficient building in Freiburg (Germany)

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Abstract

Objectives The aim of this study was to investigate the electrical properties of ileal Glucagon-like peptide 1 (GLP-1) secreting L-cells using murine organoid cultures and the electrophysiological and intracellular signaling pathways recruited following activation of the Gαq-coupled free fatty acid receptors FFA1 and Gαs-coupled bile acid receptors GPBAR1. Methods Experiments were performed using ileal organoids generated from mice transgenically expressing fluorescent reporters (Epac2-camps and GCaMP3) under control of the proglucagon promoter. Electrophysiology and single cell imaging were performed on identified L-cells in organoids, and GLP-1 secretion from cultured organoids was measured by immunoassay. Results The FFA1 ligand TAK-875 triggered L-cell electrical activity, increased intracellular calcium, and activated a depolarizing current that was blocked by the TRPC3 inhibitor Pyr3. TAK-875 triggered GLP-1 secretion was Pyr3 sensitive, suggesting that the TRPC3 channel links FFA1 activation to calcium elevation and GLP-1 release in L-cells. GPBAR1 agonist triggered PKA-dependent L-type Ca2+current activation and action potential firing in L-cells. The combination of TAK-875 and a GPBAR1 agonist triggered synergistic calcium elevation and GLP-1 secretory responses. Conclusions FFA1 and GPBAR1 activation individually increased electrical activity in L-cells by recruiting pathways that include activation of TRPC3 and L-type voltage-gated Ca2+channels. Synergy between the pathways activated downstream of these receptors was observed both at the level of Ca2+elevation and GLP-1 secretion.

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Fastenrath, S., & Braun, B. (2018). Sustainability transition pathways in the building sector: Energy-efficient building in Freiburg (Germany). Applied Geography, 90, 339–349. https://doi.org/10.1016/j.apgeog.2016.09.004

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