Design Principles of Reptilian Muscles: Calcium Cycling Strategies

Anat Rec (Hoboken). 2016 Mar;299(3):352-60. doi: 10.1002/ar.23302. Epub 2015 Dec 31.


The ultrastructure of the sarcoplasmic reticulum (SR) in skeletal muscles was compared among different reptile species (watersnake, boa constrictor, lizard, and turtle) and a mammal (mouse). Morphometric analysis demonstrates a pattern of increasing calsequestrin (CASQ) content in the lumen of SR from turtle to lizard, watersnake, and boa constrictor, and this content is in all cases higher than in mouse. In all reptiles sampled except turtle, CASQ is not confined to the junctional sarcoplasmic reticulum (jSR) cisternae as it is in other species. It instead fills the entire longitudinal (free) SR (fSR) regions, and in the extreme case of snakes, the shape of the SR is modified around the extra CASQ. We suggest that high CASQ content may represent an ATP-saving adaptation that permits relatively low metabolic rates during prolonged periods of fasting and inactivity, particularly in watersnake and boa constrictor.

Keywords: Squamata; calsequestrin; reptiles; sarcoplasmic reticulum; skeletal muscle.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calsequestrin / metabolism*
  • Mice
  • Reptiles / physiology*
  • Sarcoplasmic Reticulum / physiology*
  • Sarcoplasmic Reticulum / ultrastructure
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / metabolism*


  • Calsequestrin
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases
  • Calcium