Chronic electrical stimulation drives mitochondrial biogenesis in skeletal muscle of a lizard,Varanus exanthematicus

Abstract

SUMMARY We investigated the capacity for phenotypic plasticity of skeletal muscle from Varanus exanthematicus, the savannah monitor lizard. Iliofibularis muscle from one leg of each lizard was electrically stimulated for 8 weeks. Both stimulated and contralateral control muscles were collected and processed for electron microscopy. We used stereological analysis of muscle cross-sections to quantify the volume densities of contractile elements, sarcoplasmic reticulum, mitochondria and intracellular lipids. We found that mitochondrial volume density was approximately fourfold higher in the stimulated muscle compared to controls, which were similar to previously reported values. Sarcoplasmic reticulum volume density was reduced by an amount similar to the increase in mitochondrial volume density while the volume density of contractile elements remained unchanged. Intracellular lipid accumulation was visibly apparent in many stimulated muscle sections but the volume density of lipids did not reach a significant difference. Although monitor lizards lack the highly developed aerobic metabolism of mammals, they appear to possess the capacity for muscle plasticity.

Exhaustive exercise training enhances aerobic capacity in American alligator (Alligator mississippiensis)

“…nuchalis following an 8-week training schedule (Garland et al 1987 ), however, Garland et al ( 1987 ) also found that sedentary lizards had higher aerobic enzyme activity in thigh extensor muscles than exercise-trained lizards, contrary to what would be expected following an exercise training regime. Recently, it was demonstrated that chronic electrical stimulation for 8 weeks increases mitochondrial biogenesis in a hindlimb muscle of V. exanthematicus (Schaeffer et al 2007 ), but in a separate study, 32 treadmill training bouts at 75% of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}_{{\text{O}}_2} $$\end{document} max over 8 weeks did not increase \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}_{{\text{O}}_2} $$\end{document} max or alter myosin heavy chain expression in skeletal muscles of V. exanthematicus (A. M. Szucsik et al, unpublished). It remains to be tested whether a long-term and exhaustive training protocol, used in the present study and that on the estuarine crocodile (Owerkowicz and Baudinette 2008 ), can elicit an increase in heart mass, haematocrit or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{V}_{{\text{O}}_2} $$\end{document} max in a squamate.…”

Metabolism at the Max: How Vertebrate Organisms Respond to Physical Activity

“…Exhaustive activity training enhances VO 2max in alligators, but without any change in the mitochondrial enzyme citrate synthase activities, though it did increase relative ventricle mass and hematocrit, both variables that would increase SOT (77). Electrical stimulation of skeletal muscle in Varanus exanthematicus for 8 weeks resulted in a fourfold increase of mitochondrial volume density (223). The rattlesnake tail-shaker muscles represent the most dramatic aerobic example of reptilian muscle.…”