Cold acclimation induces proliferation of sarcoplasmic reticulum without increase in Ca2+-ATPase activity in white axial muscle of striped bass (Morone saxatilis)
✍ Scribed by Riemenschneider, William K. ;Sidell, Bruce D.
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 707 KB
- Volume
- 292
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
The effects of acclimation of striped bass to cold (5°C) and warm (25°C) temperatures upon ultrastructural features of white axial skeletal muscle are quantified. Surface density of sarcoplasmic reticulum (SR) increased by almost 30%, and SR volume density increased by about 20% during cold acclimation. Proliferation of SR suggests an increase in available SR surface for re‐sequestration of Ca^2+^ and a decrease in diffusion path length for Ca^2+^ during cold acclimation. Average cross‐sectional areas and cross‐sectional perimeters of myofibrils situated in the center of muscle fibers decreased during cold acclimation by approximately 20% and 11%, respectively. Additionally, average major and minor axes of ellipses fit to central myofibrillar cross‐sections decreased by approximately 12% and 8%, respectively, during cold acclimation. These measurements define a decrease in average myofibrillar diameter and suggest a decrease in diffusion path length for Ca^2+^ to and from myofibrillar activation sites. Measurements of peripheral myofibrils that had elongated profiles in cross‐sections indicate that maximum profile length of these myofibrils decreases by about 17%. Peripheral myofibrils may break up into smaller myofibrils with more rounded cross‐sectional profiles during cold acclimation. SR Ca^2+^‐ATPase of white axial muscle was also measured in unfractionated homogenates and in crude SR‐enriched subcellular fractions from cold‐ and warm‐acclimated striped bass. No difference in SR Ca^2+^‐ATPase activity per g wet weight was observed between cold‐ and warm‐acclimated animals. Lack of increase in SR Ca^2+^‐ATPase per g wet weight, despite a significant proliferation of SR, probably results in a decrease in average Ca^2+^‐ATPase pump density within the SR membrane during cold acclimation. Thus, compensation for decreased diffusion coefficient of Ca^2+^ during cold acclimation appears due to the combined effects of proliferation of SR surface density and a decrease in average myofibrillar diameter. J. Exp. Zool. 292:231–240, 2002. © 2002 Wiley‐Liss, Inc.