| Hummingbirds are able to fuel energetically expensive hovering flight entirely with recently ingested glucose or fructose. In other animals, several steps in the pathway of flux of sugars from the gut to muscle are rate-limiting, such as transport into muscle and subsequent phosphorylation. I examined relative expression of facilitative sugar transporters and enzymes of fructolysis in various ruby-throated hummingbird (Archilochus colubris) tissues via quantitative polymerase chain reaction. I hypothesized that the expression of these proteins would be upregulated in hummingbird flight muscle compared to other vertebrates. I found that hummingbird pectoralis displays the highest expression of certain sugar transporter transcripts among vertebrates. I also demonstrated that relative transcript densities of fructolytic enzymes are minimal in hummingbird muscle, suggesting that fructolysis is not a pathway used to rapidly metabolize fructose in these muscles. |
