title: Design Principles of Reptilian Muscles: Calcium Cycling Strategies.
abstract: 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.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Stefano
authors.initials: S
authors.lastname: Perni
authors.affiliation: Department of Biological Sciences, Williams Annex., Lehigh University, Bethlehem, Pennsylvania.
authors.forename: Matthew
authors.initials: M
authors.lastname: Close
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Clara
authors.initials: C
authors.lastname: Franzini-Armstrong
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002155:Calsequestrin / Q000378:metabolism*; D051379:Mice; D012104:Reptiles / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology* / Q000648:ultrastructure; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*
chemical_list: D002155:Calsequestrin; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium
keywords: Squamata; calsequestrin; reptiles; sarcoplasmic reticulum; skeletal muscle