Functional Segregation within the Muscles of Aquatic Propulsion in the Asiatic Water Monitor (Varanus salvator).

Bruce A Young,Peter J Reiser,Brandon Lyons,Andrew Macduff,Nicholas John,Matthew Most,Nathan A Reiser,Jessica Dumais

doi:10.3389/fphys.2016.00380

Abstract

Water monitor lizards (Varanus salvator) swim using sinusoidal oscillations generated at the base of their long (50% of total body length) tail. In an effort to determine which level of the structural/organizational hierarchy of muscle is associated with functional segregation between the muscles of the tail base, an array of muscle features—myosin heavy chain profiles, enzymatic fiber types, twitch and tetanic force production, rates of fatigue, muscle compliance, and electrical activity patterns—were quantitated. The two examined axial muscles, longissimus, and iliocaudalis, were generally similar at the molecular, biochemical, and physiological levels, but differed at the biomechanics level and in their activation pattern. The appendicular muscle examined, caudofemoralis, differed from the axial muscles particularly at the molecular and physiological levels, and it exhibited a unique compliance profile and pattern of electrical activation. There were some apparent contradictions between the different structural/organizational levels examined. These contradictions, coupled with a unique myosin heavy chain profile, lead to the hypothesis that there are previously un-described molecular/biochemical specializations within varanid skeletal muscles.

Highlights

Skeletal muscle is a dynamic tissue the functional properties of which are influenced, if not determined, at a variety of organizational levels
With the specimen lightly anesthetized with Isoflurane, sterile hypodermic needles were used to implant bipolar electromyographic (EMG) leads into the caudofemoralis, the longissimus and the iliocaudalis
The results indicate that V. salvator iliocaudalis, longissimus, and caudofemoralis muscles differ markedly from each other at multiple levels

Summary

Introduction

Skeletal muscle is a dynamic tissue the functional properties of which are influenced, if not determined, at a variety of organizational levels. The diversity of myosin isoforms, as well as other molecular components within the single muscle fiber, can produce functional heterogeneity (Bottinelli, 2001). At a higher level of organization, the dynamics of the muscle-tendon complex will depend, in part, on the pattern of neural stimulation (e.g., Lacquaniti et al, 2012). While this is widely recognized, the majority of published studies focus on a single analytical technique applied to just one level of muscle organization.

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Results

Conclusion