Meeting Abstract
50.3 Sunday, Jan. 5 10:45 Myosin heavy chain isoforms of the flight and leg muscles of hummingbird and zebra finch VELTEN, B*; WELCH, K; University of Toronto; University of Toronto brandy.velten@mail.utoronto.ca
The maximum shortening velocity of a muscle fiber is strongly correlated with the myosin heavy chain (MHC) isoforms it contains. While MHC isoforms of mammalian skeletal muscle are well characterized, less is known about avian MHC isoforms or how they correlate to fiber type. Avian flight muscles are primarily composed of fast-twitch fibers [fast glycolytic (FG) and/or fast oxidative, glycolytic (FOG)], and it’s been suggested that FG and FOG fibers can have different MHC isoforms. Wingbeat frequency, and thus, muscle strain rate, also differ across species, ranging from 2.5-80 Hz. Ruby-throated hummingbirds (Archilochus colubris) and zebra finches (Taeniopygi guttata) have relatively high wingbeat frequencies (25-65 Hz), requiring rapid shortening of their flight muscles, which are composed exclusively of FOG fibers. We examined whether the MHC isoform(s) present in the pectoralis and supracoracoideus of these species differed from that present in the chicken superficial pectoralis, which contracts at a slower rate and is composed of FG fibers. Leg muscles were also examined as they are of mixed fiber type and play a more postural role. MHC isoforms were separated using SDS-PAGE electrophoresis. Primarily fast isoforms were observed in the leg muscles of both species, but isoforms varied between muscles, with some exhibiting multiple isoforms including those associated with slow tonic fibers. Flight muscles of both species had only one MHC isoform corresponding to the adult fast isoform of the chicken. Although these muscles likely operate at faster shortening speeds, this finding suggests that the strain rates associated with flight led to a convergence of flight muscle MHC isoforms across species. Other properties of muscle, such as myosin light chain isoforms, may also play a role in varying shortening velocities across species.
