Comparative Characteristics of Sarcoplasmic Reticulum Preparations from Skeletal Muscles of the Ground Squirrel Spermophilus undulatus, Rats, and Rabbits

A. N. Shutova¹, K. B. Storey², O. D. Lopina¹, and A. M. Rubtsov^1*

¹Department of Biochemistry, School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (7-095) 939-3955; E-mail: amr@atpase.bio.msu.su

²Department of Biology and Department of Chemistry, Carleton University, Ottawa K1S 5B6, Canada; fax: (613) 520-2569; E-mail: kbstorey@ccs.carleton.ca

^* To whom correspondence should be addressed.

Received May 21, 1999; Revision received June 21, 1999

---

A comparison of sarcoplasmic reticulum (SR) preparations from skeletal muscles of ground squirrels Spermophilus undulatus, rats, and rabbits established that on the basis of protein yield and phospholipid/protein ratio these preparations are practically the same. Nevertheless, the specific activity of Ca-ATPase, the main protein component of SR membranes, in SR preparations of the ground squirrel skeletal muscles is only about half of the activity in SR preparations of rats and rabbits. Significant differences in protein composition of the preparations were detected: ground squirrel SR differed by an unusually high content of a 205 kD protein (probably myosin) and a number of low-molecular-weight SR protein components, and the SR preparations of rabbits are characterized by a high content of the Ca-binding proteins calsequestrin and sarcalumenin. Use of the anionic carbocyanine dye Stains-All established that all preparations contained only three proteins which are stained dark blue by this dye: calsequestrin, sarcalumenin, and a histidine-rich Ca-binding protein. The electrophoretic mobility of calsequestrin was identical in all preparations (molecular mass 63 kD), whereas sarcalumenin and histidine-rich Ca-binding protein are probably present in different isoforms with molecular masses of 130, 145, and 160 and 165, 155, and 170 kD, respectively, in SR preparations of ground squirrels, rats, and rabbits. Analysis of the fluorescence parameters of the fluorescent probes 8-anilino-1-naphthalene sulfonic acid and pyrene bound to SR membranes showed that the properties of the lipid bilayer in the SR membranes of the preparations differed considerably. It is suggested that the differences in protein composition and/or structural state of the ground squirrel SR membrane lipid bilayer could be the reason for the low Ca-ATPase activity in these preparations.

---

KEY WORDS: sarcoplasmic reticulum, Ca-ATPase, Ca-binding proteins, calsequestrin, sarcalumenin, histidine-rich Ca-binding protein, ground squirrel Spermophilus undulatus

---