The effect of UCP2 and UCP3 on ATP concentrations varies depending on cell type. For example, pancreatic beta cells experience a decrease in ATP concentration with increased activity of UCP2. This is associated with cell degeneration, decreased insulin secretion, and type II diabetes. Conversely, UCP2 in hippocampus cells and UCP3 in muscle cells stimulate production of mitochondria. The larger number of mitochondria increases the combined concentration of ADP and ATP, actually resulting in a net increase in ATP concentration when these uncoupling proteins become coupled (i.e. the mechanism to allow proton leaking is inhibited).