Effects of ischemia on sarcoplasmic reticulum Ca2+ uptake and Ca2+ releasein rat skeletal muscle

In this study, we investigated the hypothesis that prolonged ischemia would impair both sarcoplasmic reticulum (SR) Ca2+ uptake and Ca2+ release in sk eletal muscle. To induce total ischemia (I), a tourniquet was placed around the upper hindlimb in 30 female Sprague-Dawley rats [wt = 256 +/- 6.7 (SE) g] and inflated to 350 mmHg for 4 h. The contralateral limb served as cont rol (C). Immediately after the 4 h of ischemia, mixed gastrocnemius and tib ialis anterior muscle was sampled from both limbs, and both crude muscle ho mogenates and SR vesicles were prepared. In another 10 control animals (CC) , muscles were sampled and prepared exactly the same way, but immediately a fter anesthetization. Ca2+ uptake and Ca2+ release were measured in vitro w ith Indo-I on both homogenates and SR vesicles. As hypothesized, submaximal Ca2+ uptake was lower (P< 0.05) in I compared with CC and C, by 25 and 45% in homogenates and SR vesicles, respectively. Silver nitrate (AgNO3)-induc ed Ca2+ release, which occurred in two phases (phase 1 and phase 2), was al so altered in I compared with CC and C, in both muscle homogenates and SR v esicles. With ischemia, phase 1 peak Ca2+ release was 26% lower (P< 0.05) i n SR vesicles only. For phase 2, peak Ca2+ release was 54 and 24% lower (P< 0.05) in SR vesicles and homogenates, respectively. These results demonstr ate that prolonged skeletal muscle ischemia leads to a reduced SR Ca2+ upta ke in both homogenates and SR vesicles. The effects of ischemia on SR Ca2release, however, depend on both the phase examined and the type of tissue preparation.