| dc.description.abstract | The ATP-sensitive potassium (KATP) channel is a vital link between cellular metabolism and electrical excitability in a variety of cell types, including pancreatic beta cells and hypothalamic neurons where they are involved in the response to changing plasma glucose levels. Blockade of KATP channels using sulfonylureas is a common therapeutic target for Type 2 diabetes (T2D) treatment. However, long-term sulfonylurea therapy is associated with a 33% chance of failure, reducing overall drug efficacy and pancreatic beta cell function, reducing their lasting effectiveness. Furthermore, gain-of-function mutations in KATP channels, leading to NDM and DEND syndrome, can drastically alter basal cellular metabolism and mitochondrial function, indicating a potential role of KATP channel activity in the regulation of glucose metabolism. In addition, DEND mutations have been shown to cause a wide array of neurological conditions, currently untreatable with sulfonylurea therapy. The aim of these studies was to answer three main questions; what is the impact of chronic blockade on membrane conductance and KATP channel activity after removal of the drug? does the alteration of KATP channel activity to regulate cellular glucose metabolism? And lastly, what concentration does memantine block native KATP channels at? Chapter 3 presents evidence that both gliclazide (5 μM) and tolbutamide (50 μM) caused a significant augmentation of KATP-mediated membrane conductance in GT1-7 cells after 48 hours of treatment of ~2x and 1.5x, respectively. Overall, these data provide an alternative explanation to the increased rate of drug failure after long term therapy with sulfonylureas. Chapter 4 shows that the acute modulation of KATP channel activity caused little to no significant alterations in either glycolysis or mitochondrial activity, as has been previously described. However, chronic KATP channel blockade with glibenclamide increased mitochondrial ATP production and decreased basal glycolysis, potentially as a response to increased cellular excitability. Chapter 5 shows that external exposure of GT1-7 cells to memantine (100 μM) caused significant reduction in KATP-dependent whole-cell membrane conductance (~80% maximal). However, no significant effect was observed at either 10 μM or 1 μM memantine. Overall, these data suggest that memantine does block KATP channels, but at a much higher concentration than is therapeutically relevant. Overall, this work provides new evidence that supplements our understanding of both the impacts of pharmacological treatment on KATP channel activity, as well as the role of KATP channel activity on cellular glucose metabolism. Furthermore, and most importantly, this work furthers our understanding of the effects of memantine on KATP mediated membrane conductance and its effectiveness, or lack thereof, as a novel treatment for NDM. | en_GB |
