Type 2 diabetes mellitus remains an enormous health burden. Pancreatic islet dysfunction underlies the development of diabetes and while it is recognised that communication between cells within the islet is essential for proper function, the mechanism responsible is unknown. Connexin 36 is expressed on beta cells and is important for coordinated pulsatile insulin release. The interaction between pancreatic islets and endothelial cells was investigated in vitro. Islets were isolated from C57B6 mice and endothelial cells were grown from C57B6 bone marrow and confirmed to express endothelial markers (CD31 and E-selectin), bind lectin and uptake acetylated low-density lipoprotein by flow cytometry. To investigate soluble mechanisms, islets were cultured with endothelial cell-conditioned medium and tested for glucose-stimulated insulin release. Secreted insulin was detected by high-sensitivity ELISA and stimulation indices (SI) were calculated as insulin secretion at high glucose divided by basal insulin secretion. Endothelial cell-conditioned islets had an increased level of basal insulin release (0.7±0.22 ng/min/mg; n=7) compared to controls (0.2±0.04 ng/min/mg; n=6; p<0.05). However, they had a reduced ability to upregulate insulin release in response to high glucose (SI=1.3±0.5 compared to 4.2±0.9 for controls; p<0.05). Gene expression was analysed by real-time PCR using Taqman primers (normalizing to B2m) following non-contact co-cultures where islets were cultured in transwells above endothelial monolayers. Co-cultured islets significantly down-regulated the expression of connexin 36 (0.4±0.05 fold relative to control islets; n=18; p<0.05). These data suggest that connexin 36 expression is modulated during intercellular communication between beta cells and endothelial cells, resulting in dysregulated insulin release. We suggest this represents a ‘survival’ islet phenotype, where baseline insulin secretion is maintained during vascular remodelling. This mechanism may have relevance for islet physiology, where the function and survival of beta cells is critically dependent on the presence of intra-islet vascular endothelium.