SZUCSIK, Amanda M.*; BENNETT, Albert F.; HICKS, James W.; University of California-Irvine; University of California-Irvine; University of California-Irvine: The Effects of Joint Immobilization on Skeletal Muscle Plasticity in Varanus exanthematicus

Reptiles are purported to possess limited plasticity in their oxygen transport system upon exposure to various forms of chronic physiological stress. This lack of plasticity is evident in the reptiles� apparent inability to respond physiologically to aerobic exercise training at the organismal as well as (macro)molecular levels. To determine whether Savannah monitor lizards (Varanus exanthematicus) demonstrate evidence of skeletal muscle plasticity in response to reduced use, we employed joint immobilization as a means to impose atrophic and hypertrophic stimuli. Control lizards (n = 6) were euthanized immediately upon acquisition for the purpose of obtaining baseline values of measured parameters. The gastrocnemius muscle was excised from these lizards bilaterally and subsequently analyzed for total protein concentration, cross-sectional area, and MHC isoform gene/protein expression. The right ankle joint of experimental lizards was immobilized in either complete plantarflexion (atrophic stimulus; n = 6) or complete dorsiflexion (hypertrophic stimulus; n = 5) for a period of 4 weeks. Experimental lizards were euthanized at the conclusion of the 4 week protocol, following which the gastrocnemius muscle was excised bilaterally, analyzed for aforementioned indices of plasticity, and compared to the results obtained from control muscle. Preliminary data suggest that V. exanthematicus� physiological response to reduced muscle use is different from that previously demonstrated by members of other vertebrate groups. Supported by NSF Grant IBN0091308 to AFB and JWH.