Increase in oxidative capacity of pigeon pectoralis muscle before and after fledging

Abstract

Using the pectoralis muscle of the pigeon (Columba livia), we previously showed that at fledging, both fast-twitch oxidative-glycolytic (FOG) and fast-twitch glycolytic (FG) fiber types retain a myosin isoform characteristic of the neonatal period, despite the birds being at adult body mass. Our aim here was to test the hypothesis that muscle fibers of the pigeon pectoralis increase their aerobic capacity both before and after fledging. Pigeons aged from 1 week after hatching through to adulthood were used. Adopting a microdensitometric technique from studies on mammalian muscle, the activity of succinate dehydrogenase (SDH) within individual fibers was quantified as optical density and used as an index of aerobic capacity. We demonstrate a strong linear correlation (r2 = 0.936) between optical density of FOG fibers and time exposed to the SDH incubation medium. Optical density of FG fibers, however, could not be discerned from background staining. SDH activity in FOG fibers increased logarithmically (r2 = 0.969) with the age of the birds, increasing 2.5-fold from 1 week through to adult. Thus, aerobic capacity did increase both before and after fledging. In addition, within FOG fibers, aerobic capacity and myosin content appear to have different timetables of development.