title: Muscle ultrastructure and biochemistry of lowland Tibetans.
abstract: Muscle ultrastructure and biochemistry in vastus lateralis muscle biopsies and the response to exercise of 8 lowland Tibetans (T) were compared with those of 8 Nepalese lowlanders (N). Blood hemoglobin was lower in T than in N (119 +/- 3 vs. 131 +/- 2 g/l; P < 0.05). Peak O2 consumption per kilogram of body mass was similar [37.9 +/- 2.2 (T) vs. 40.1 +/- 1.36 ml.min-1.kg body mass-1 (N)]. Maximum exercise blood lactate was the same [11.4 (T) +/- 0.5 vs. 11.3 +/- 0.6 mM (N)]. Muscle fiber type distribution was similar [type I, 58.6 +/- 3.4 (N) vs. 57.0 +/- 3.4% (T); type IIa, 24.1 +/- 3.5 vs. 27.1 +/- 1.6%; type IIb, 17.4 +/- 1.4 vs. 15.9 +/- 2.9%]. T had smaller fiber cross-sectional areas [3,413 +/- 677 (T) vs. 3,895 +/- 447 microns 2 (N); P < 0.05] but had similar number of capillaries per muscle fiber [1.35 +/- 0.23 (T) vs. 1.46 +/- 0.08 (N)] and muscle fiber area supplied per capillary [399 +/- 29 (T) vs. 382 +/- 65 mm2 (N)]. Total mitochondrial volume density was much lower in T (3.99 +/- 0.17%) than in N (5.51 +/- 0.19%) (P < 0.025). Mirroring mitochondrial volume density, citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were lower in T than in N (P < 0.05). The activities of L-lactate dehydrogenase and hexokinase were the same in both groups. T had significantly less muscle fiber lipid droplets than did N, which correlated with the low activity of 3-hydroxyacyl-CoA dehydrogenase (r = 0.57, P = 0.02). In conclusion, lowland-born T have a low mitochondrial volume-to-specific peak O2 consumption ratio, which, based on previous measurements on altitude-born Sherpas (B. Kayser, H. Hoppeler, H. Claassen and P. Cerretelli. J. Appl. Physiol. 70: 1938-1942, 1991), appears to be an inborn feature.
authors.affiliation: Département de Physiologie, Centre Médical Universitaire, Geneva, Switzerland. kayser@cmu.unige.ch
authors.forename: B
authors.initials: B
authors.lastname: Kayser
authors.forename: H
authors.initials: H
authors.lastname: Hoppeler
authors.forename: D
authors.initials: D
authors.lastname: Desplanches
authors.forename: C
authors.initials: C
authors.lastname: Marconi
authors.forename: B
authors.initials: B
authors.lastname: Broers
authors.forename: P
authors.initials: P
authors.lastname: Cerretelli
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000531:Altitude; D015308:Anaerobic Threshold / Q000502:physiology; D001823:Body Composition / Q000502:physiology; D001827:Body Height / Q000502:physiology; D001835:Body Weight; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D005260:Female; D006651:Histocytochemistry; D006801:Humans; D008297:Male; D008931:Mitochondria, Muscle / Q000378:metabolism / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000648:ultrastructure*; D009390:Nepal; D012885:Skinfold Thickness; D018609:Tibet