Reptilian Skeletal Muscle: Fiber-Type Composition and Enzymatic Profile in the Lizard, Iguana iguana

• Published in: Copeia 1986-05, Vol.1986 (2), p.324-332
• Main Authors: Gleeson, Todd T., Harrison, Jon M.
• Format: Article
• Language: English
• Subjects: Animal physiology; Animals; Biological and medical sciences; Bones; Citrates; Dehydrogenases; Energy metabolism; Fundamental and applied biological sciences. Psychology; Iguanas; Lizards; Muscles; Skeletal muscle; Striated muscle. Tendons; Vertebrates: osteoarticular system, musculoskeletal system
• ISSN: 0045-8511; 1938-5110
• DOI: 10.2307/1444993

The iliofibularis (IF) muscle in Iguana iguana was evaluated to determine its histochemical fiber-type composition in animals ranging in mass from 25-216 g. The red and white regions of the muscle were also separated and the maximal enzyme activities of citrate synthase (CS), β-hydroxyacyl CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH) of the two regions were measured to evaluate their capacity for oxidative metabolism, β-oxidation and glycolytic energy production. The IF was composed of all three fiber types typical of other lizard species. Fast-twitch glycolytic fibers (FG) occupied 60% of the total cross-sectional area. The fast-twitch oxidative glycolytic (FOG) and tonic fiber types were restricted to an oxidative region of the muscle, with tonic fibers accounting for 75% of the oxidative region area. Over the range of body mass examined, oxidative fiber diameters and muscle cross-sectional areas increased with mass at a greater rate than predicted by principles of geometric similarity. Oxidative fiber types (FOG and tonics) exhibited four times the CS activity of FG fibers. LDH/CS ratios indicated that FG fibers had eight times the glycolytic capacity of the oxidative types. Although absolute HOAD activities in FG fibers were lower, HOAD/CS ratios were slightly greater (50%) than those of FOG and tonic fibers (P = .036). Characteristics of fiber types in I. iguana seem similar in most respects to those of other iguanid lizards. The data also support earlier evidence that Iguana muscles are composed of more tonic fibers and fewer FOG fibers than muscles of other iguanid lizards.