Heat exposure does not alter eccentric exercise-induced increases in mitochondrial calcium and respiratory dysfunction

Abstract

Eccentric exercise can lead to muscle damage including dramatic changes to mitochondrial calcium content (MCC) and impaired respiratory function. Heat acclimation can create a cross-tolerance to a number of stresses including eccentric exercise but little is known about any protection to mitochondria. We hypothesised that intermittent heat exposure will lead to improved control of MCC and to preserved mitochondrial function following eccentric exercise. Sprague-Dawley rats were exposed to 3 weeks of intermittent heat exposure (36°C, 40% relative humidity, 6 h/day, 5 days a week) or kept in cool conditions (20°C). Animals were then assigned to a control or exercise group (-14°C decline treadmill exercise for 90 min). MCC, mitochondrial respiration and mitochondrial permeability transition pore opening (mPTP) were measured in mitochondria isolated from the red quadriceps in animals killed immediately, 2 h and 48 h post-exercise. Results showed that heat exposure was associated with lower plasma creatine kinase levels (p < 0.05) post-exercise suggesting lower levels of muscle damage. There was a significant (~500%) rise in MCC (p < 0.001) and a reduction in mitochondrial respiratory control ratio (p < 0.001) 48 h post-exercise. mPTP displayed increased (p < 0.05) sensitivity to calcium immediately and 48 h post-exercise. Thus, decline running led to significant impairment of mitochondria respiration and calcium loading which was more pronounced 48 h post-exercise compared with earlier time points. MCC levels and mitochondrial function were not altered by heat exposure. In conclusion, intermittent heat exposure does not appear to provide protection against mitochondrial dysfunction resulting from eccentric exercise.

Specific training improves skeletal muscle mitochondrial calcium homeostasis after eccentric exercise

“…Downhill treadmill running is known to cause substantial damage to the vastus intermedius, vastus medialis and vastus lateralis (Armstrong et al 1983) in rats. The protocol has previously been shown to result in mitochondrial dysfunction (Rattray et al 2011). …”

“…Mitochondrial calcium content was determined using a method previously described by our group (Rattray et al 2011). An aliquot (10 ll) of the isolated mitochondria was transferred to a cuvette containing 2 ml of 0.15 M PBS, pH 7.4 and Indo-1 (3 ll).…”

“…Mitochondria were isolated as previously described (Rattray et al 2011). Red muscle tissue was separated from visual fat and connective tissue and cut up with scissors in ice-cold isolation buffer (100 mM sucrose, 100 mM KCl, 50 mM Tris, 100 lM EGTA, 1.6 lM Ruthenium Red, 1 mM KH 2 PO 4 , 0.2 % BSA adjusted to pH 7.4).…”

“…High calcium concentrations can occur following forms of eccentric exercise (Sonobe et al 2008;Duan et al 1990), but only some (Magalhaes et al 2009;Molnar et al 2006) and not all (Madsen et al 1996a;Molnar et al 2006) studies have reported altered mitochondrial respiration indices posteccentric exercise. Recently, it was shown that 48 h post a bout of eccentric exercise, when large elevations in mitochondrial calcium content are present, mitochondrial respiratory function is impaired (Rattray et al 2011). The mechanisms behind this impairment are likely to be varied and changes in mitochondrial calcium content may directly or indirectly alter mitochondrial respiration (Madsen et al 1996b).…”

Ameliorative Effects of Caffeic Acid Phenethyl Ester on an Eccentric Exercise-Induced Skeletal Muscle Injury by Down-Regulating NF-kB Mediated Inflammation

“…Proper physical activity is well known to be beneficial for preventing chronic diseases; however, improperly performing exercise or sport activities, for instance muscles undergoing eccentric contraction during downhill walking or running, leads to muscle damage involving cell membrane disruption, mitochondrial dysfunction, inflammation, and muscle performance impairment lasting for several days following exercise [12,13]. The eccentric exercise induces skeletal muscle damage by inducing neutrophil and macrophage infiltration [14,15] to the site of injury within several hours, and this may last for up to 24 or even 48 h after exercise [16].…”