Meeting Abstract
65.6 Jan. 7 Biochemical stoichiometry affects whole-animal oxygen consumption rate in vivo WELCH, KC*; SUAREZ, RK; Univ. of California, Santa Barbara; Univ. of California, Santa Barbara k_welch@lifesci.ucsb.edu
The stoichiometric relationship of molecular oxygen consumption to ATP production is known to vary as a function of the metabolic substrate used. The P/O ratio of isolated mitochondria oxidizing fatty acids is lower than when pyruvate is oxidized while perfused hearts using fat consume more O2 than when using carbohydrate. Whether this matters at the level of the whole animal is not known. In the present study, we hypothesized that VO2 should decline as RQ increases from 0.7 to 1.0 to reflect these stoichiometric relationships in hovering hummingbirds (Selasphorus rufus and Calypte anna) as they transition from fasted to fed states. Under controlled conditions in which metabolic power input requirements are expected to be constant, we show that oxygen consumption is significantly greater when fats are metabolized compared to when carbohydrates are metabolized. The effect of metabolic substrate on oxygen consumption rate remains robust after accounting for small changes in hummingbird mass over the course of the experiment. The average difference in oxygen consumption rate between states in which individuals are oxidizing fats versus carbohydrates is remarkably similar to the differences observed at the mitochondrial level and as predicted by current estimates of substrate-dependent P/O ratios. This study highlights the importance of knowledge of oxidized substrates whenever respirometry is employed as a means of inferring whole-animal metabolic power input.
