Activation of the sarcoplasmic reticulum Ca2+-ATPase induced by exercise.
Prolonged exercise has been shown to cause disruption of intracellular calcium homeostasis in skeletal muscle, which is normally maintained by the sarcoplasmic reticulum (SR) Ca2+-ATPase. We have investigated the response of this enzyme to increased intracellular calcium levels by investigating the functional and physical characteristics of the SR Ca2+-ATPase and membrane lipids following 2 h of treadmill running and throughout a period of post-exercise recovery. The Ca2+-ATPase of SR membranes purified from exercised rats shows increases in enzymatic activity correlating with post-exercise recovery time. Corresponding increases in active Ca2+-ATPase pump units are observed, as measured by the concentration of phosphorylated enzyme intermediate formed from ATP. However, catalytic turnover rates of the Ca2+-ATPase are unchanged. Using spin-label electron paramagnetic resonance to assess both membrane fluidity and associations between individual Ca2+-ATPase polypeptide chains, we find no exercise-induced alterations in membrane dynamics which could explain the observed increases in Ca2+-ATPase activity. Nor do we find evidence for altered membrane purification as a result of exercise. We suggest that the cell responds to the challenge of increased cytosolic calcium levels by increasing the proportion of functional SR Ca2+-ATPase proteins in the membrane for the rapid restoration of calcium homeostasis.
Ferrington
D A
DA
Department of Biochemistry, University of Kansas, Lawrence, 66045, USA.
Reijneveld
J C
JC
Bär
P R
PR
Bigelow
D J
DJ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D003402:Creatine Kinase / Q000097:blood / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation; D006706:Homeostasis; D008297:Male; D008560:Membrane Fluidity; D018482:Muscle, Skeletal / Q000201:enzymology; D010766:Phosphorylation; D010805:Physical Conditioning, Animal; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013113:Spin Labels
D013113:Spin Labels; D003402:Creatine Kinase; D000252:Calcium-Transporting ATPases; D002118:Calcium