Effects of tissue fractionation on exercise-induced alterations in SR function in rat gastrocnemius muscle

Abstract

Because studies into exercise-induced alterations in sarcoplasmic reticulum (SR) Ca2+ sequestration have produced conflicting reports, we have hypothesized that the differences in SR Ca(2+)-adenosinetriphosphatase (ATPase) activity and Ca2+ uptake in SR fractions observed in different studies are due to different SR isolation techniques. To investigate this possibility, rat white and red gastrocnemius muscles from control and run animals were studied by using two conventional isolation techniques to obtain a crude microsomal fraction and an isolated SR vesicle (SRV) fraction. Indexes of CM and SRV function were compared with measurements from whole muscle homogenate. Treadmill running to exhaustion did not alter SR protein yields, percent SR extraction, or basal or Ca(2+)-ATPase purification in either fraction. Ca(2+)-activated ATPase activity was not altered by exercise in any of the fractions examined, but Ca2+ uptake was reduced in the homogenates (9.48 +/- 1.4 to 6.90 +/- 0.8 nmol . mg-1.min-1) and SRV fractions (84.0 +/- 11.5 to 50.7 +/- 14.0 nmol . mg-1.min-1) from the red gastrocnemius at free Ca2+ concentrations of 600-700 nM. These data indicate that reductions in SR Ca2+ uptake are dissociated from changes in Ca(2+)-ATPase in vitro and occur only in a specific population of vesicles. The mechanisms underlying these alterations are not known but may involve a reduction in the number of Ca(2+)-ATPase enzymes or a selective sedimentation of damaged vesicles in the SRV fraction.

Effects of prolonged exercise and recovery on sarcoplasmic reticulum Ca2+ cycling properties in rat muscle homogenates

“…When the exercise was extended to fatigue, representing some 50–60 min of additional exercise, no further reductions in V max were observed. Our current findings support previous research from our laboratory in which we have been unable to detect reductions in V max behaviour of the Ca 2+ ‐ATPase with prolonged exercise measured in both crude homogenates (Chin & Green 1996) and SR vesicles (Chin et al. 1994, Chin & Green 1996).…”

“…Our current findings support previous research from our laboratory in which we have been unable to detect reductions in V max behaviour of the Ca 2+ ‐ATPase with prolonged exercise measured in both crude homogenates (Chin & Green 1996) and SR vesicles (Chin et al. 1994, Chin & Green 1996). As in previous studies, our results could not be attributed to changes in basal or Mg 2+ ‐ATPase activity, since no changes were observed either with exercise or during recovery.…”

“…1993), suggesting a structural modification to the Ca 2+ ‐release channel (Favero 1999). As emphasized, the discrepancy between this study and previous reports could arise from the same factors, namely differences in the preparation used and/or differences in the fibre composition of the muscles examined (Chin & Green 1996).…”

Altered sarcoplasmic reticulum function in rat diaphragm after high‐intensity exercise

“…Although there are conflicting reports in the literature (Chin & Green 1996), the results from some previous studies on the effect of acute exercise on SR function indicate a qualitative agreement with those observed in chronic stimulation experiments (Byrd et al . 1989a, Booth et al .…”

Effect of exercise on sarcoplasmic reticulum Ca<sup>2+</sup> transport in muscle of mouse lines long-term selected for different Performance traits

“…This hypothesis could not be verified. Contradictory results conceming Ca 2+ uptake and Ca 2+ ATPase are intensely discussed to be at least in part a result of different sample preparation DOSSETT-MERCER et al, 1995;CHIN and GREEN, 1996). To circumvent uncertainties in the SR isolation technique, homogenates were used in this investigation.…”