Ischemia-induced structural change in SR Ca2+-ATPase is associated with reduced enzyme activity in rat muscle

ATP consumption by sarcoplasmic reticulum Ca²⁺ pumps accounts for 40-50% of resting metabolic rate in mouse fast and slow twitch skeletal muscle

The main purpose of this study was to directly quantify the relative contribution of Ca²⁺ cycling to resting metabolic rate in mouse fast (extensor digitorum longus, EDL) and slow (soleus) twitch skeletal muscle. Resting oxygen consumption of isolated muscles (VO₂, µL/g wet weight/s) measured polarographically at 30^°C was ~20% higher (P<0.05) in soleus (0.326 ± 0.022) than in EDL (0.261 ± 0.020). In order to quantify the specific contribution of Ca²⁺ cycling to resting metabolic rate, the concentration of MgCl₂ in the bath was increased to 10 mM to block Ca²⁺ release through the ryanodine receptor, thus eliminating a major source of Ca²⁺ leak from the sarcoplasmic reticulum (SR), and thereby indirectly inhibiting the activity of the sarco(endo) plasmic reticulum Ca²⁺-ATPases (SERCAs). The relative (%) reduction in muscle VO₂ in response to 10 mM MgCl₂ was similar between soleus (48.0±3.7) and EDL (42.4±3.2). Using a different approach, we attempted to directly inhibit SERCA ATPase activity in stretched EDL and soleus muscles (1.42x optimum length) using the specific SERCA inhibitor cyclopiazonic acid (CPA, up to 160 µM), but were unsuccessful in removing the energetic cost of Ca²⁺ cycling in resting isolated muscles. The results of the MgCl₂ experiments indicate that ATP consumption by SERCAs is responsible for 40–50% of resting metabolic rate in both mouse fast- and slow-twitch muscles at 30^°C, or 12–15% of whole body resting VO₂. Thus, SERCA pumps in skeletal muscle could represent an important control point for energy balance regulation and a potential target for metabolic alterations to oppose obesity.

Distribution of internal pressure around bony prominences: implications to deep tissue injury and effectiveness of intermittent electrical stimulation

The overall goal of this project is to develop interventions for the prevention of deep tissue injury (DTI), a form of pressure ulcers that originates in deep tissue around bony prominences. The present study focused on: (1) obtaining detailed measures of the distribution of pressure experienced by tissue around the ischial tuberosities, and (2) investigating the effectiveness of intermittent electrical stimulation (IES), a novel strategy for the prevention of DTI, in alleviating pressure in regions at risk of breakdown due to sustained loading. The experiments were conducted in adult pigs. Five animals had intact spinal cords and healthy muscles and one had a spinal cord injury that led to substantial muscle atrophy at the time of the experiment. A force-controlled servomotor was used to load the region of the buttocks to levels corresponding to 25%, 50% or 75% of each animal's body weight. A pressure transducer embedded in a catheter was advanced into the tissue to measure pressure along a three dimensional grid around the ischial tuberosity of one hind leg. For all levels of external loading in intact animals, average peak internal pressure was 2.01 ± 0.08 times larger than the maximal interfacial pressure measured at the level of the skin. In the animal with spinal cord injury, similar absolute values of internal pressure as that in intact animals were recorded, but the substantial muscle atrophy produced larger maximal interfacial pressures. Average peak internal pressure in this animal was 1.43 ± 0.055 times larger than the maximal interfacial pressure. Peak internal pressure was localized within a ±2 cm region medio-laterally and dorso-ventrally from the bone in intact animals and ±1 cm in the animal with spinal cord injury. IES significantly redistributed internal pressure, shifting the peak values away from the bone in spinally intact and injured animals. These findings provide critical information regarding the relationship between internal and interfacial pressure around the ischial tuberosities during loading levels equivalent to those experienced while sitting. The information could guide future computer models investigating the etiology of DTI, as well as inform the design and prescription of seating cushions for people with reduced mobility. The findings also suggest that IES may be an effective strategy for the prevention of DTI.

Flavonoids in prevention of diseases with respect to modulation of Ca-pump function

Flavonoids, natural phenolic compounds, are known as agents with strong antioxidant properties. In many diseases associated with oxidative/nitrosative stress and aging they provide multiple biological health benefits. Ca²⁺-ATPases belong to the main calcium regulating proteins involved in the balance of calcium homeostasis, which is impaired in oxidative/nitrosative stress and related diseases or aging. The mechanisms of Ca²⁺-ATPases dysfunction are discussed, focusing on cystein oxidation and tyrosine nitration. Flavonoids act not only as antioxidants but are also able to bind directly to Ca²⁺-ATPases, thus changing their conformation, which results in modulation of enzyme activity.

Dysfunction of Ca²⁺-ATPases is summarized with respect to their posttranslational and conformational changes in diseases related to oxidative/nitrosative stress and aging. Ca²⁺-ATPases are discussed as a therapeutic tool and the possible role of flavonoids in this process is suggested.

Initiating treadmill training in late middle age offers modest adaptations in Ca2+ handling but enhances oxidative damage in senescent rat skeletal muscle

Aging skeletal muscle shows an increased time to peak force and relaxation and a decreased specific force, all of which could relate to changes in muscle Ca(2+) handling. The purpose of this study was to determine if Ca(2+)-handling protein content and function are decreased in senescent gastrocnemius muscle and if initiating a training program in late middle age (LMA, 29 mo old) could improve function in senescent (34- to 36-mo-old) muscle. LMA male Fischer 344 x Brown-Norway rats underwent 5-7 mo of treadmill training. Aging resulted in a decrease in maximal sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity and a decrease in Ca(2+) release rate but no change in Ca(2+) uptake rate. Efficiency of the Ca(2+) pump was increased with age, as was the content of SERCA2a. Training caused a further increase in SERCA2a content. Aging also caused an increase in protein carbonyl and reactive nitrogen species damage accumulation, and both further increased with training. Consistent with the increase in oxidative damage, heat shock protein 70 content was increased with age and further increased with training. Together, these results suggest that while initiating exercise training in LMA augments the age-related increase in expression of heat shock protein 70 and the more efficient SERCA2a isoform, it did not prevent the decrease in SERCA activity and exacerbated oxidative damage in senescent gastrocnemius muscle.

ATP consumption by sarcoplasmic reticulum Ca2+ pumps accounts for 50% of resting metabolic rate in mouse fast and slow twitch skeletal muscle

In this study, we aimed to directly quantify the relative contribution of Ca(2+) cycling to resting metabolic rate in mouse fast-twitch (extensor digitorum longus, EDL) and slow-twitch (soleus) skeletal muscle. Resting oxygen consumption of isolated muscles (Vo(2), microl.g wet wt(-1).s(-1)) measured polarographically at 30 degrees C was approximately 25% higher in soleus (0.61 +/- .03) than in EDL (0.46 +/- .03). To quantify the specific contribution of Ca(2+) cycling to resting metabolic rate, cyclopiazonic acid (CPA), a highly specific inhibitor of sarco(endo)plasmic reticulum Ca(2+) ATPases (SERCAs), was added to the bath at different concentrations (1, 5, 10, and 15 microM). There was a concentration-dependent effect of CPA on Vo(2), with increasing CPA concentrations up to 10 microM resulting in progressively greater reductions in muscle Vo(2). There were no differences between 10 and 15 microM CPA, indicating that 10 microM CPA induces maximal inhibition of SERCAs in isolated muscle preparations. Relative reduction in muscle Vo(2) in response to CPA was nearly identical in EDL (1 microM, 10.6 +/- 3.0%; 5 microM, 33.2 +/- 3.4%; 10 microM, 49.2 +/- 2.9%; 15 microM, 50.9 +/- 2.1%) and soleus (1 microM, 11.2 +/- 1.5%; 5 microM, 37.7 +/- 2.4%; 10 microM, 50.0 +/- 1.3%; 15 microM, 49.9 +/- 1.6%). The results indicate that ATP consumption by SERCAs is responsible for approximately 50% of resting metabolic rate in both mouse fast- and slow-twitch muscles at 30 degrees C. Thus SERCA pumps in skeletal muscle could represent an important control point for energy balance regulation and a potential target for metabolic alterations to oppose obesity.

Investigating the role of ischemia vs. elevated hydrostatic pressure associated with acute obstructive uropathy

Obstructive uropathy can cause irreversible renal damage. It has been hypothesized that elevated hydrostatic pressure within renal tubules and/or renal ischemia contributes to cellular injury following obstruction. However, these assaults are essentially impossible to isolate in vivo. Therefore, we developed a novel pressure system to evaluate the isolated and coordinated effects of elevated hydrostatic pressure and ischemic insults on renal cells in vitro. Cells were subjected to: (1) elevated hydrostatic pressure (80 cm H(2)O); (2) ischemic insults (hypoxia (0% O(2)), hypercapnia (20% CO(2)), and 0 mM glucose media); and (3) elevated pressure + ischemic insults. Cellular responses including cell density, lactate dehydrogenase (LDH) release, and intracellular LDH (LDH(i)), were recorded after 24 h of insult and following recovery. Data were analyzed to assess the primary effects of ischemic insults and elevated pressure. Unlike pressure, ischemic insults exerted a primary effect on nearly all response measurements. We also evaluated the data for insult interactions and identified significant interactions between ischemic insults and pressure. Altogether, findings indicate that pressure may sub-lethally effect cells and alter cellular metabolism (LDH(i)) and membrane properties. Results suggest that renal ischemia may be the primary, but not the sole, cause of cellular injury induced by obstructive uropathy.

Protective effects of Hsp70 on the structure and function of SERCA2a expressed in HEK-293 cells during heat stress

Heat shock protein 70 (Hsp70) can physically interact with and prevent thermal inactivation of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) 1a, the SERCA isoform expressed in adult fast-twitch skeletal muscle. This study examined whether Hsp70 could physically interact with and prevent thermal inactivation of SERCA2a, the SERCA isoform expressed in heart. HEK-293 cells were cotransfected with cDNAs encoding human Hsp70 and rabbit SERCA2a (S2a/Hsp70). Cells cotransfected with SERCA2a cDNA and pMT2 (S2a/pMT2) were used as control. One-half of the cells was heat shocked at 40 degrees C for 1 h (HS), and one-half was maintained at 37 degrees C before harvesting the cells and isolating microsomes. Western blot analysis showed that Hsp70 and SERCA2a were colocalized in the microsomal fraction. The levels of Hsp70 were approximately fivefold higher (P < 0.05) in S2a/Hsp70 compared with S2a/pMT2 and approximately twofold higher (P < 0.05) following HS in all cells. Coimmunoprecipitation demonstrated that Hsp70 directly binds to SERCA2a. Following HS, maximal SERCA2a activity was reduced ( approximately 52%, P < 0.05) in S2a/pMT2 but was increased ( approximately 33%, P < 0.05) in S2a/Hsp70. Thermal inactivation of SERCA2a in S2a/pMT2 was associated with decreased ( approximately 49%, P < 0.05) binding capacity for fluorescein isothiocyanate (FITC) and increased carbonyl ( approximately 42%, P < 0.05) and nitrotyrosine ( approximately 40%, P < 0.05) levels in SERCA2a. By contrast, the HS-induced increase in maximal SERCA2a activity observed in S2a/Hsp70 corresponded with no change (P > 0.05) in FITC-binding capacity and reductions in carbonyl ( approximately 40%, P < 0.05) and nitrotyrosine ( approximately 23%, P < 0.05) levels in SERCA2a compared with S2a/pMT2. These results show that Hsp70 forms a protective interaction with SERCA2a during HS actually reducing oxidation and nitrosylation of SERCA2a thus increasing its maximal activity.

Interaction between Hsp70 and the SR Ca2+pump: a potential mechanism for cytoprotection in heart and skeletal muscle

The overexpression of heat shock protein 70 (Hsp70) provides cytoprotection to cells, making them resistant to otherwise lethal levels of stress. In this review, the role Hsp70 plays in protecting both cardiac and skeletal muscle against the pathophysiological effects of oxidative stress are examined, with a focus on the molecular basis for the cytoprotective effects of Hsp70. The ability of Hsp70 to maintain cell survival undoubtedly involves the regulation of multiple steps within apoptotic pathways, but could also involve the regulation of key upstream mediators of apoptosis (i.e., oxidative stress, Ca2+overload). Hsp70 can stabilize the structure and function of both the skeletal muscle and cardiac Ca2+pump under heat stress conditions. Given that Ca2+overload has long been implicated in cell death, Hsp70 might protect muscle cells by maintaining cellular Ca2+homeostasis, thereby preventing the initiation of apoptosis. The functional interaction between Hsp70 and Ca2+pumps might also promote improvements in muscle contractility after exposure to oxidative stress.

Alterations in in vitro function and protein oxidation of rat sarcoplasmic reticulum Ca2+-ATPase during recovery from high-intensity exercise

The hypothesis tested in this study was that the extent to which sarcoplasmic reticulum (SR) Ca(2+)-ATPase is oxidized would correlate with a decline in its activity. For this purpose, changes in the SR Ca(2+)-sequestering ability and the contents of carbonyl and sulfhydryl groups during recovery after exercise were examined in the superficial portions of vastus lateralis muscles from rats subjected to 5 min running at an intensity corresponding to maximal oxygen uptake (50 m min(-1), 10% gradient). A single bout of exercise elicited a 22.4% reduction (P < 0.05) in SR Ca(2+)-ATPase activity. The decreased activity progressively reverted to normal levels during recovery after exercise, reaching normal levels after 60 min of recovery. This change was paralleled by a depressed SR Ca(2+)-uptake rate, and the proportional alteration in these two variables resulted in no change in the ratio of Ca(2+)-uptake rate to Ca(2+)-ATPase activity. The contents of SR Ca(2+)-ATPase protein and sulfhydryl groups in microsomes were unchanged after exercise and during recovery periods. In contrast, the content of carbonyl groups in SR Ca(2+)-ATPase behaved in an opposite manner to that of SR Ca(2+)-ATPase activity. An approximately 80% augmentation (P < 0.05) in the carbonyl group content occurred immediately after exercise. The elevated carbonyl content decreased towards normal levels during 60 min of recovery. These results are strongly suggestive that oxidation of SR Ca(2+)-ATPase is responsible, at least in part, for a decay in the SR Ca(2+)-pumping function produced by high-intensity exercise and imply that oxidized proteins may be repaired during recovery from exercise.

Effects of buthionine sulfoximine treatment on diaphragm contractility and SR Ca2+ pump function in rats

The purpose of this study was to examine the effects of glutathione (GSH) depletion and cellular oxidation on rat diaphragm contractility and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) function in vitro under basal conditions and following fatiguing stimulation. Buthionine sulfoximine (BSO) treatment (n = 10) for 10 days (20 mM in drinking water) reduced (P < 0.05) diaphragm GSH content (nmol/mg protein) and the ratio of GSH to glutathione disulfide (GSH/GSSG) by 91% and 71%, respectively, compared with controls (CTL) (n = 10). Western blotting showed that Hsp70 expression in diaphragm was not increased (P > 0.05) with BSO treatment. As hypothesized, basal peak twitch force (g/mm(2)) was increased (P < 0.05), and fatigability in response to repetitive stimulation (350-ms trains at 100 Hz once every 1 s for 5 min) was also increased (P < 0.05) in BSO compared with CTL. Both Ca(2+) uptake and maximal SERCA activity (mumol.g protein(-1).min(-1)) measured in diaphragm homogenates that were prepared at rest were increased (P < 0.05) with BSO treatment, an effect that could be partly explained by a twofold increase (P < 0.05) in SERCA2a expression with BSO. In response to the 5-min stimulation protocol, both Ca(2+) uptake and maximal SERCA activity were increased (P < 0.05) in CTL but not (P > 0.05) in BSO diaphragm. We conclude that 1) cellular redox state is more optimal for contractile function and fatigability is increased in rat diaphragm following BSO treatment, 2) SERCA2a expression is modulated by redox signaling, and 3) regulation of SERCA function in working diaphragm is altered following BSO treatment.

Prevention of pressure-induced deep tissue injury using intermittent electrical stimulation

Pressure ulcers develop due to morphological and biochemical changes triggered by the combined effects of mechanical deformation, ischemia, and reperfusion that occur during extended periods of immobility. The goal of this study was to test the effectiveness of a novel electrical stimulation technique in the prevention of deep tissue injury (DTI). We propose that contractions elicited by intermittent electrical stimulation (IES) in muscles subjected to constant pressure would induce periodic relief in internal pressure; additionally, each contraction would also restore blood flow to the tissue. The application of constant pressure to the quadriceps muscles of rats generated a DTI that affected 60 ± 15% of the compressed muscle as assessed by magnetic resonance imaging. In contrast, in the groups of rats that received IES at 10- and 5-min intervals, DTI of the muscle was limited to 16 ± 16 and 25 ± 13%, respectively. Injury to the muscle was corroborated by histology. In an experiment with a human volunteer, compression of the buttocks reduced the oxygenation level of the muscles by ∼4%; after IES, oxygenation levels increased by ∼6% beyond baseline. Concurrently, the surface pressure profiles of the loaded muscles were redistributed and the high-pressure points were reduced during each IES-induced contraction. The results of this study indicate that IES significantly reduces the amount of DTI by increasing the oxygen available to the tissue and by modifying the pressure profiles of the loaded muscles. This presents a promising technique for the prevention of pressure ulcers in immobilized and/or insensate individuals.

Sarcolemmal damage in dystrophin deficiency is modulated by synergistic interactions between mechanical and oxidative/nitrosative stresses

Dystrophin deficiency is the cause of Duchenne muscular dystrophy, but the precise physiological basis for muscle necrosis remains unclear. To determine whether dystrophin-deficient muscles are abnormally susceptible to oxidative and nitric oxide (NO)-driven tissue stress, a hindlimb ischemia/reperfusion (I/R) model was used. Dystrophic mdx mice exhibited abnormally high levels of lipid peroxidation and protein nitration, which were preceded by exaggerated NO production during ischemia. Visualization of NO with the fluorescent probe 4,5-diaminofluorescein diacetate suggested that excess NO production during ischemia occurred within a subset of mdx fibers. In mdx muscles only, prior exposure to I/R dramatically increased the level of sarcolemmal damage resulting from stretch-mediated mechanical stress, indicating greatly exacerbated hyperfragility of the dystrophic fiber membrane. Treatment with NO synthase inhibitors (l-N(G)-nitroarginine methyl ester hydrochloride or 7-nitroindazol) effectively blocked the synergistic interaction between I/R and mechanical stress-mediated sarcolemmal damage under these conditions. Taken together, our findings provide direct ex-perimental evidence that several prevailing hy-potheses regarding the cause of muscle fiber damage in dystrophin-deficient muscle can be integrated into a common pathophysiological framework involving interactions between oxidative stress, ab-normal NO regulation, and hyperfragility of the sarcolemma.

Differential effects of repetitive activity on sarcoplasmic reticulum responses in rat muscles of different oxidative potential

We investigated the hypothesis that muscles of different oxidative potential would display differences in sarcoplasmic reticulum (SR) Ca2+ handling responses to repetitive contractile activity and recovery. Repetitive activity was induced in two muscles of high oxidative potential, namely, soleus (SOL) and red gastrocnemius (RG), and in white gastrocnemius (WG), a muscle of low oxidative potential, by stimulation in adult male rats. Measurements of SR properties, performed in crude homogenates, were made on control and stimulated muscles at the start of recovery (R0) and at 25 min of recovery (R25). Maximal Ca2+-ATPase activity (Vmax, micromol x g protein(-1) x min(-1)) at R0 was lower in stimulated SOL (105 +/- 9 vs. 135 +/- 7) and RG (269 +/- 22 vs. 317 +/- 26) and higher (P < 0.05) in WG (795 +/- 32 vs. 708 +/- 34). At R25, Vmax remained lower (P < 0.05) in SOL and RG but recovered in WG. Ca2+ uptake, measured at 2,000 nM, was depressed (P < 0.05) in SOL and RG by 34 and 13%, respectively, in stimulated muscles at R0 and remained depressed (P < 0.05) at R25. In contrast, Ca2+ uptake was elevated (P < 0.05) in stimulated WG at R0 by 9% and remained elevated (P < 0.05) at R25. Ca2+ release, unaltered in SOL and RG at both R0 and R25, was increased (P < 0.05) in stimulated WG at both R0 and R25. We conclude that SR Ca2+-handling responses to repetitive contractile activity and recovery are related to the oxidative potential of muscle.

Beta2-agonist administration increases sarcoplasmic reticulum Ca2+-ATPase activity in aged rat skeletal muscle

Aging is associated with a slowing of skeletal muscle contractile properties, including a decreased rate of relaxation. In rats, the age-related decrease in the maximal rate of relaxation is reversed after 4-wk administration with the beta2-adrenoceptor agonist (beta2-agonist) fenoterol. Given the critical role of the sarcoplasmic reticulum (SR) in regulating intracellular Ca2+ transients and ultimately the time course of muscle contraction and relaxation, we tested the hypothesis that the mechanisms of action of fenoterol are mediated by alterations in SR proteins. Sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) kinetic properties were assessed in muscle homogenates and enriched SR membranes isolated from the red (RG) and white (WG) portions of the gastrocnemius muscle in adult (16 mo) and aged (28 mo) F344 rats that had been administered fenoterol for 4 wk (1.4 mg/kg/day ip, in saline) or vehicle only. Aging was associated with a 29% decrease in the maximal activity (Vmax) of SERCA in the RG but not in the WG muscles. Fenoterol treatment increased the Vmax of SERCA and SERCA1 protein levels in RG and WG. In the RG, fenoterol administration reversed an age-related selective nitration of the SERCA2a isoform. Our findings demonstrate that the mechanisms underlying age-related changes in contractile properties are fiber type dependent, whereas the effects of fenoterol administration are independent of age and fiber type.

Effects of progressive exercise and hypoxia on human muscle sarcoplasmic reticulum function

This study examined the effects of progressive exercise to fatigue in normoxia (N) on muscle sarcoplasmic reticulum (SR) Ca2+cycling and whether alterations in SR Ca2+cycling are related to the blunted peak mechanical power output (POpeak) and peak oxygen consumption (V̇o2 peak) observed during progressive exercise in hypoxia (H). Nine untrained men (20.7 ± 0.42 yr) performed progressive cycle exercise to fatigue on two occasions, namely during N (inspired oxygen fraction = 0.21) and during H (inspired oxygen fraction = 0.14). Tissue extracted from the vastus lateralis before exercise and at power output corresponding to 50 and 70% of V̇o2 peak(as determined during N) and at fatigue was used to investigate changes in homogenate SR Ca2+-cycling properties. Exercise in H compared with N resulted in a 19 and 21% lower ( P < 0.05) POpeakand V̇o2 peak, respectively. During progressive exercise in N, Ca2+-ATPase kinetics, as determined by maximal activity, the Hill coefficient, and the Ca2+concentration at one-half maximal activity were not altered. However, reductions with exercise in N were noted in Ca2+uptake (before exercise = 357 ± 29 μmol·min−1·g protein−1; at fatigue = 306 ± 26 μmol·min−1·g protein−1; P < 0.05) when measured at free Ca2+concentration of 2 μM and in phase 2 Ca2+release (before exercise = 716 ± 33 μmol·min−1·g protein−1; at fatigue = 500 ± 53 μmol·min−1·g protein−1; P < 0.05) when measured in vitro in whole muscle homogenates. No differences were noted between N and H conditions at comparable power output or at fatigue. It is concluded that, although structural changes in SR Ca2+-cycling proteins may explain fatigue during progressive exercise in N, they cannot explain the lower POpeakand V̇o2 peakobserved during H.

Ca2+-regulatory muscle proteins in the alcohol-fed rat

Alcoholic myopathy is characterized by muscle weakness and difficulties in gait and locomotion. It is one of the most prevalent skeletal muscle disorders in the Western hemisphere, affecting between 40% and 60% of all chronic alcohol misusers. However, the pathogenic mechanisms are unknown, although recent studies have suggested that membrane defects occur as a consequence of chronic alcohol exposure. It was our hypothesis that alcohol ingestion perturbs membrane-located proteins associated with intracellular signalling and contractility, in particular those relating to calcium homeostasis. To test this, we fed male Wistar rats nutritionally complete liquid diets containing ethanol as 35% of total dietary energy. Controls were pair-fed identical amounts of the same diet in which ethanol was replaced by isocaloric glucose. At the end of 6 weeks, rats were killed and skeletal muscles dissected. These were used to determine important ion-regulatory skeletal muscle proteins including sarcalumenin (SAR), sarcoplasmic-endoplasmic reticulum Ca(2+)-adenosine triphosphatase (ATPase) (SERCA1), the junctional face protein of 90 kd (90-JFP), alpha(1)- and alpha(2)-dihydropyridine receptor (alpha(1)-DHPR and alpha(2)-DHPR), and calsequestrin (CSQ) by immunoblotting. The relative abundance of microsomal proteins was determined by immunoblotting using the enhanced chemiluminescence (ECL) technique. The data showed that alcohol-feeding significantly reduced gastrocnemius and hind limb muscle weights (P <.05 in both instances). Concomitant changes included increases in the relative amounts of SERCA1 (P <.05) and Ca(2+)-ATPase activity (P <.025). However, there were no statistically significant changes in either SAR, 90-JFP, alpha(1)-DHPR or alpha(2)-DHPR (P >.2 in all instances). Reductions in CSQ were of marginal significance (P =.0950). We conclude that upregulation of SERCA1 protein and Ca(2+)-ATPase activity may be an adaptive mechanism and/or a contributory process in the pathology of alcohol-induced muscle disease.

Free radical-induced protein modification and inhibition of Ca2+-ATPase of cardiac sarcoplasmic reticulum

The effect of oxidative stress on the Ca2+-ATPase activity, lipid peroxidation and protein modification of cardiac sarcoplasmic reticulum (SR) membranes was investigated. Isolated SR vesicles were exposed to FeSO4/EDTA (0.2 micromol Fe2+ per mg of protein) at 37 degrees C for 1 h in the presence or absence of antioxidants. FeSO4/EDTA decreased the maximum velocity of Ca2+-ATPase reaction without a change of affinity for Ca2+ or Hill coefficient. Treatment with radical-generating system led also to conjugated diene formation, loss of sulfhydryl groups, changes in tryptophan and bityrosine fluorescences and to production of lysine conjugates with lipid peroxidation end-products. Lipid antioxidants butylated hydroxytoluene (BHT) and stobadine partially prevented inhibition of Ca2+-ATPase and decrease in tryptophan fluorescence, while the loss of -SH groups and formation of bityrosines or lysine conjugates were completely prevented. Glutathione also partially protected Ca2+-ATPase activity and decreased formation of bityrosine, but it was not able to prevent oxidative modification of tryptophan and lysine. These findings suggest that combination of amino acid modifications, rather than oxidation of amino acids of one kind, is responsible for inhibition of SR Ca2+-ATPase activity.