Meeting Abstract
Hummingbirds rely entirely on recently ingested carbohydrates to fuel rested and exercising metabolism as well as the de novo synthesis of lipids. Their flight muscle cells have the capacity for rapid phosphorylation of both imported glucose and fructose. Facilitative glucose transporters (GLUTs) regulate the flux of glucose and fructose across biological plasma membranes (PMs) and into active cells. We examined ruby-throated hummingbird (Archilochus colubris) flight muscle and liver for changes in GLUT protein abundance and localization in response to feeding. We observed GLUT-5 protein in the flight muscle PM, supporting previous findings that suggest a unique fructose-processing capacity of hummingbird flight muscle. We also show the lack of GLUT-1 protein in hepatocytes, despite previously observed GLUT-1 transcript. Finally, we found that feeding increases the PM abundance of glucose-specific GLUT-isoforms (GLUT-1) in the flight muscle, while the liver PM increases in both glucose- and fructose-specific GLUT-proteins (GLUT-2, GLUT-3). This suggests that, while hummingbird muscle show capacity for fructose import and phosphorylation, only glucose-specific GLUT-isoforms are dynamically regulated in response to feeding. In the liver, both glucose- and fructose-specific GLUT-isoforms are dynamically regulated suggesting that the liver may predominately transport ingested fructose. This study provides further insights into how hummingbirds manage the partitioning of recently ingested glucose and fructose to optimize their daily energy needs.
