Studying the Effects of Glucagon-Modulators on the Activity of Second Messengers in Subcellular Compartments of Pancreatic Islet Cells

The convergence of multiple paracrine, juxtacrine, and intracellular signals is necessary to achieve proper glucagon secretion from the α-cells of the pancreatic islet. Elevated or dysregulated secretion of glucagon severely impairs the glycemic control of diabetic patients. Thus it is important to clarify how all these stimuli co-operate and interact to stimulate and or inhibit glucagon secretion. Using hyperspectral fluorescence microscopy, we measure the effect of glucagon modulators, insulin, somatostatin, and ephrins simultaneously on the activity of two second messengers, calcium and cyclic adenosine monophosphate (cAMP), in islet cells. We target genetically encoded biosensors to the cytoplasm, to the plasma membrane or to the nucleus. We hypothesize that in response to different stimuli, second messengers’ activities change differently in various cell compartments. Individual stimuli or their combination result in various patterns of activities, which we can use to improve our current mathematical model of glucose-inhibited glucagon secretion. These studies utilize both cell line models and primary cultured islet cells. This combination of specimens allows us to determine the conditions under which we can rely on cell lines to mimic intact islets hormone output. Having a reliable cell model for glucagon secretion form α-cells will be very beneficial for drug screening studies.