Meeting Abstract
Ruby-throated hummingbirds (Archilochus colubris) power energetically expensive behaviour almost entirely with recently ingested carbohydrates. When fasting, hummingbirds are capable of supporting metabolism entirely with endogenous fatty acid oxidation. Within 20-30 minutes of the start of foraging on floral nectar hummingbirds, can switch to fueling their metabolism entirely with ingested sugar. This rapid and complete fuel switch implies high capacities for sugar uptake and delivery to active tissues. Their enlarged heart, high heart rate, high vascularisation, and fast-acting digestive, glycolytic, and oxidative enzymes all contribute to rapid transport and breakdown of fuel. Less understood is the transmembrane transport of carbohydrates, regulated by the SLC2 family of hexose transporters, the glucose transporters (GLUTs) and their potential role in regulating this fuel switch. Hummingbirds lack insulin-responsive GLUT4 and don’t exhibit an insulin-mediated blood glucose response. Thus, other GLUT isoforms (e.g. GLUT1, 2, 3, and 5) must play a key role in blood sugar regulation and high tissue uptake capacities in hummingbirds. Using an imunohistochemical approach, we are characterizing subcellular localisation of A. colubris GLUTs in several tissues in response to availability of carbohydrates. We hypothesize that carbohydrate ingestion will increase co-localisation of GLUTs 1, 2, 3, and 5 with the cell-surface membranes within 20-30 minutes and decrease when fasted. This may provide an insight into a unique glucose sensing and hexose-regulating system that both operates at a rapid pace and is also insulin independent.
