Blood glucose is maintained at the appropriate concentration by insulin released from β-cells and glucagon released from α-cells, both integrated within the pancreatic islet of Langerhans. The secretory processes in both types of cells are triggered by a rise in intracellular calcium concentration ([Ca2+]i). Endocrine disrupting chemicals (EDC) are hormone-like agents present in the environment that alter the endocrine system of wildlife and humans. Most EDC have potencies far below those of the natural hormone 17β-E2 when acting through the classic estrogen receptors (ERs).
Swiss albino OF1 male mice (8-10 weeks old) were humanly killed by cervical dislocation according to national guidelines. Pancreatic islets of Langerhans were isolated by collagenase digestion and loaded with 5 µM Fluo-3 AM for at least 1 h at room temperature. Calcium records in individual cells within the islet were obtained by imaging intracellular calcium under a Zeiss LSM 510 confocal microscope using a Zeiss X 40 oil immersion lens, numerical aperture 1.3. Experiments were performed at 34 °C. α and β-cells within the islets were identified by their [Ca2+]i oscillatory pattern in 0.5 mM and 8 mM glucose, respectively (Nadal et al. 1999).
Using the technique described above, we have shown that the environmental estrogens Bisphenol-A, the synthetic oestrogen diethylstilbestrol (DES) and the native hormone 17β-E2 abolished [Ca2+]i oscillations in glucagon releasing α-cells within intact islet of Langerhans. The pesticide o.p’-DDT which has a slightly different chemical structure presented a more reduced effect. This action was rapid in onset and it was reproduced by the membrane impermeable molecule E2 conjugated to horseradish peroxidase (E-HRP) and were not blocked by the antioestrogen ICI182, 780. Therefore, low-dose of EDC regulates [Ca2+]i signals via an alternative pathway, initiated at the plasma membrane. Competition studies performed with E-HRP binding in single isolated α-cells supported the idea that the membrane binding site involved is nonclassical oestrogen membrane receptor (ncmER). This receptor has the characteristics of that previously described in pancreatic β-cells (Nadal et al. 2000; Ropero et al. 2002).
This work is funded by grants from Instituto de Salud Carlos III RCMN (C03/08) and Ministerio de Ciencia y Tecnologia (BFI2002-01469).