SUMMARY Insulin secretion from pancreatic β–cells is dependent on maturation and acidification of the secretory granule necessary for prohormone convertase cleavage of proinsulin. Previous studies in isolated β–cells revealed that acidification may be dependent on the granule membrane chloride channel ClC-3, in a step permissive for a regulated secretory response. In this study, immuno-electron microscopy of β–cells revealed colocalization of ClC-3 and insulin on secretory granules. Clc-3−/− mice as well as isolated islets demonstrate impaired insulin secretion; clc3−/− β–cells are defective in regulated insulin exocytosis and granular acidification. Increased amounts of proinsulin were found in the majority of secretory granules in the clc-3−/− mice while in clc3+/+ cells, proinsulin was confined to the immature secretory granules. These results demonstrate that in pancreatic β–cells chloride channels, specifically ClC-3, are localized on insulin granules and play a role in insulin processing as well as insulin secretion through regulation of granular acidification.

The use of microencapsulation with alginate-poly-l-lysine (PLL) as the encapsulation material has been hampered by overgrowth of collagen around implanted capsules. Studies have shown that poly(ethylene glycol) (PEG) has higher biocompatibility than PLL. In this project, we examined the biocompatibility of PEG in comparison with PLL in the Lewis rat model. Capsules made from either PEG or PLL were implanted into Lewis rats in three anatomical sites: subcutaneous (SC), intramuscular (IM), and intra-epididymis (IE). After 2 or 4 weeks, capsules were retrieved, sectioned, and stained with Sirius Red for analysis of fibrotic overgrowth with ImageJ software. The results were statistically analyzed using either unpaired t test or analysis of variance (ANOVA). PEG demonstrated significantly better biocompatibility in SC, at both 2 and 4 weeks, and IE at 2 weeks (p < 0.0001). No significant differences were found in IM implantation at either time point (p = 0.36) between the two materials. However, there was significantly heavier fibrotic overgrowth around PEG capsules in IE than PLL capsules at 4 weeks (p < 0.01). When compared among the anatomical sites, IM implantation demonstrated significantly less fibrotic overgrowth than other sites for both materials (p < 0.01). In conclusion, PLL and PEG may induce different levels of fibrosis based on anatomical location and duration of implantation.