Effects of 4-h ischemia and 1-h reperfusion on rat muscle sarcoplasmic reticulum function

Abstract

To investigate the hypothesis that ischemia and reperfusion would impair sarcoplasmic reticulum (SR) Ca2+ regulation in skeletal muscle, Sprague-Dawley rats ( n = 20) weighing 290 ± 3.5 g were randomly assigned to either a control control (CC) group, in which only the effects of anesthetization were studied, or to a group in which the muscles in one hindlimb were made ischemic for 4 h and allowed to recover for 1 h (I). The nonischemic, contralateral muscles served as control (C). Measurements of Ca2+-ATPase properties in homogenates and SR vesicles, in mixed gastrocnemius and tibialis anterior muscles, indicated no differences between groups on maximal activity, the Hill coefficient, and Ca50, defined as the Ca2+concentration needed to elicit 50% of maximal activity. In homogenates, Ca2+ uptake was lower ( P < 0.05) by 20–25%, measured at 0.5 and 1.0 μM of free Ca2+ ([Ca2+]f) in C compared with CC. In SR vesicles, Ca2+ uptake was lower ( P < 0.05) by 30–38% in I compared with CC at [Ca2+]f between 0.5 and 1.5 μM. Silver nitrate induced Ca2+ release, assessed during both the initial, early rapid ( phase 1), and slower, prolonged late ( phase 2) phases, in homogenates and SR vesicles, indicated a higher ( P < 0.05) release only in phase 1in SR vesicles in I compared with CC. These results indicate that the alterations in SR Ca2+ regulation, previously observed after prolonged ischemia by our group, are reversed within 1 h of reperfusion. However, the lower Ca2+ uptake observed in long-term, nonischemic homogenates suggests that altered regulation may occur in the absence of ischemia.