title: Capillary-to-fiber geometry and mitochondrial density in hummingbird flight muscle.
abstract: We investigated structural characteristics for high O2 flux in hummingbird flight muscle, i.e. the most O2 demanding skeletal muscle per unit tissue mass among vertebrates. Pectoralis and supracoracoideus muscles of 3-4 g hummingbirds (Selaphorus rufus) were perfusion fixed in situ, processed for electron microscopy and analyzed by morphometry. Small fiber size (group mean +/- SE, 201 +/- 14 microns 2 at 2.1 microns sarcomere length), large capillary length per fiber volume (8947 +/- 869 mm-2) and high mitochondrial volume density per volume of muscle fiber (34.5 +/- 0.9%) were characteristic features of the muscles. Considering capillary supply and mitochondrial volume on an individual fiber basis showed that the size of the capillary-to-fiber interface (i.e. capillary surface per fiber surface) was also high in the muscles. Comparison with mammalian hindlimb pointed to a major role of the size of the capillary-to-fiber interface in providing a great potential for O2 flux rate from capillary to muscle fiber mitochondria in hummingbird flight muscle.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla 92093-0623.
authors.forename: O
authors.initials: O
authors.lastname: Mathieu-Costello
authors.forename: R K
authors.initials: RK
authors.lastname: Suarez
authors.forename: P W
authors.initials: PW
authors.lastname: Hochachka
mesh_terms: D000818:Animals; D001717:Birds / Q000033:anatomy & histology* / Q000378:metabolism; D002196:Capillaries / Q000033:anatomy & histology; D005260:Female; D005426:Flight, Animal / Q000502:physiology; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism / Q000648:ultrastructure; D009132:Muscles / Q000098:blood supply* / Q000378:metabolism / Q000648:ultrastructure; D010101:Oxygen Consumption