Partial ischemia reduces the efficiency of sarcoplasmic reticulum Ca2+ transport in rat EDL

To investigate the hypothesis that prolonged partial ischemia would result in a depression in homogenate sarcoplasmic reticulum (SR) Ca2+-sequestering and mechanical properties in muscle, a cuff was placed around the hindlimb of 8 adult Sprague-Dawley rats (267 +/- 5.8 g; ((x)) over bar +/- S.E.) and partially inflated (315 mm Hg) for 2 h. Following occlusion, the EDL was sampled both from the ischemic (I) and contralateral control (C) leg and SR properties compared with the EDL muscles extracted from rats (n = 8) immediately following anaesthetization (CC). Ischemia was indicated by a lower (p < 0.05) concentration (mmol.kg dry wt(-)1) of ATP (19.0 +/- 0.7 vs. 16.7 +/- 0.7) and phosphocreatine (58.1 +/- 5.7 vs. 35.0 +/- 4.6) in I compared to C. Although Ca2+-ATPase activity (mu mol.g protein(-1).sec(-1)), both maximal and submaximal, was not different between C and I (19.7 +/- 0.4 vs. 18.5 +/- 1.3), reductions (p < 0.05) in Ca2+-uptake (mmol.g protein (-1).sec(-1) ) of between 18.2 and 24.7% across a range of submaximal free Ca2+-levels were observed in I compared to C. Lower submaximal Ca2+-ATPase activity and Ca2+-uptake were also observed in the EDL in C compared to CC animals. Time dependent reductions (p < 0.05) were found in peak twitch and maximal tetanic tension in EDL from I but not C. It is concluded that partial ischemia, resulting in modest reductions in energy state in EDL, induces a reduction in Ca2+-uptake independent of changes in Ca2+-ATPase activity. These changes reduce the coupling ratio and the efficiency of Ca2+-transport by SR.