Histochemistry, innervation, capillary density and mitochondrial volume of red and white muscle fibres isolated from a lizard, Varanus exanthematicus

Fiber types in the iliofibularis muscle of the savannah monitor lizard, Varanus exanthematicus, have been characterized on the basis of their histochemical characteristics and nerve endings. Four types of fibers were identified, three of which were focally innervated and the other, multiply innervated. They corresponded to the fast glycolytic, fast oxidative glycolytic, slow oxidative, and tonic fiber types of other lower vertebrates. The fibers isolated from the white and most of the fibers from the red regions had well defined end plates. However, 15 to 20% of the fibers isolated from the red region possessed an average of 17 ± 0.5 end plates per fiber. These end plates were placed 922 ± 54 μm apart and poorly defined. The mitochondrial volume of fibers isolated from the red region (12 ± 0.5%) was six times that of fibers isolated from the white region (2 ± 0.1%). Myofibrillar volumes were similar in fibers isolated from the two regions (81 ± 0.6%, white; 77 ± 0.2%, red). However, the capillary density of fibers from the red region (932 ± 64/mm2) was four and one-half times that of fibers isolated from the corresponding white region (200 ± 35/mm2).