Slow locomotion in chameleons: Histochemical and ultrastructural characteristics of muscle fibres isolated from the iliofibularis muscle of Jackson's chameleon (Chameleo jacksonii).

The histochemical and ultrastructural characteristics of the fiber types present in the iliofibularis muscle isolated from Jackson's chameleon, Chamaeleo jacksonii, have been characterized in an attempt to explain the slow locomotion of these lizards. On the basis of their histochemical characteristics and nerve endings, four types of fibers were identified corresponding to the fast glycolytic (FG), fast oxidative glycolytic (FOG), slow oxidative (SO), and tonic fibers of other lower vertebrates. Three of these fiber types (FG, FOG, and SO) were focally innervated, and the other type (tonic fibers) multiply innervated. All the fibers isolated from the clear region and most of the fibers isolated from the yellow region had single well-defined endplates. However, 20 to 28% of the fibers isolated from the yellow region possessed an average of 13 ± 0.6 endplates per fiber. The endplates in these fibers were poorly defined, 62 ± 2 μm in length, and 952 ± 40 μm apart. The mitochondrial volume of fibers isolated from the yellow region (8 ± 0.5%) was three times higher than that of fibers isolated from the clear region (2.45 ± 0.2%). In addition, the fibers isolated from the yellow region had three times the number of capillaries surrounding them as those recorded for fibers isolated from the clear region (1.95 ± 0.12 and 0.67 ± 0.09 capillaries per fiber, respectively). Fibers isolated from both regions had similar myofibrillar volume densities (91 ± 0.57, clear; 95 ± 0.87, yellow).