Ischemia-induced alterations in sarcoplasmic reticulum Ca(2+)-ATPase activity in rat soleus and EDL muscles

Abstract

To investigate the time-dependent effects of ischemia, as modified by muscle fiber type composition, on sarcoplasmic reticulum (SR) function, Ca(2+)-ATPase activity (total minus basal) was measured in homogenates prepared from samples obtained from rat soleus and extensor digitorum longus (EDL) muscle of ischemic and contralateral controls. Ischemia was induced by occlusion of blood flow to one hindlimb for periods of 1, 2, and 3 h (n = 10 per group). In EDL, maximal Ca(2+)-ATPase activity (expressed in mumol.g wet wt-1.min-1) was higher (P < 0.05) in ischemic than in control at 1 h (80 +/- 10 vs. 56.5 +/- 5.3) and increased progressively with ischemia at both 2 h (88 +/- 4.6 vs. 53.1 +/- 2.8) and 3 h (116 +/- 3.8 vs. 67.8 +/- 3.2). In contrast, in soleus, increases (P < 0.05) in Ca(2+)-ATPase activity with ischemia were observed at 2 h (19.2 +/- 0.86 vs. 14.0 +/- 0.56) and 3 h (19.9 +/- 1.4 vs. 12.4 +/- 0.62) but not at 1 h (10.7 +/- 1.5 vs. 10.0 +/- 0.83). In both EDL and soleus, basal Mg(2+)-ATPase was unchanged with ischemia. On the basis of these findings, it can be concluded that ischemia results in an increase in the maximal SR Ca(2+)-ATPase activity but that the time course of the change is dependent on the fiber type composition of the muscle.

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

“…Since the increase in Ca 2+ -ATPase activity observed in recovery appears to be due to recruitment of inactive enzyme and not to increases in catalytic rate (Ferrington et al 1996, Schertzer et al 2003, it is possible that changes in enzyme aggregation status and/or enzyme folding could account for our findings (Martonosi 1996, Froemming & Ohlendieck 1998. Regardless of the mechanism, it would appear to extend to both types I and II fibres of varying oxidative potential since we have shown previously, using short-term exercise (Green et al 1996b) and ischaemia (Green et al 1996a), that increases in V max can occur in muscles with a range of fibre type composition. It is noteworthy that we have also observed in this study that when the recovery is passive, the overshoot in Ca 2+ -ATPase activity and Ca 2+ -uptake is even more pronounced than during active recovery.…”

“…Regardless of the mechanism, it would appear to extend to both types I and II fibres of varying oxidative potential since we have shown previously, using short‐term exercise (Green et al. 1996b) and ischaemia (Green et al. 1996a), that increases in V max can occur in muscles with a range of fibre type composition.…”

Effect of 10‐day cast immobilization on sarcoplasmic reticulum calcium regulation in humans

“…In this study only one [Ca 2+ ] f was used to determine Ca 2+ ATPase activity, and it is possible that maximal activity occurs at a different [Ca 2+ ] f following atrophy. However another study of Ca 2+ ATPase activity at different [Ca 2+ ] f found that activity was maximal at the same [Ca 2+ ] f before and after ischaemia (Green et al 1996).…”

“…The decrease in SR Ca 2+ uptake observed with immobilization under optimal conditions indicated an intrinsic alteration in the SR and was not paralleled by a decrease in SR Ca 2+ ATPase activity. However another study of Ca 2+ ATPase activity at different [Ca 2+ ] f found that activity was maximal at the same [Ca 2+ ] f before and after ischaemia (Green et al 1996). First, there may have been an uncoupling of the SR membrane pump.…”

“…Five assays were performed for each muscle sample, with the mean value used. The reaction was initiated with the addition of 1.1 mM CaCl 2 , corresponding to a free Ca 2+ concentration ([Ca 2+ ] f ) of 12.1 lM (Green et al 1996). After 60 s, 36 mM CaCl 2 was added for a further 120 s to completely inhibit the Ca 2+ ATPase activity, in order to determine the basal Ca 2+ ATPase activity.…”