Efficacy of a web-based cognitive rehabilitation intervention for adult cancer survivors: A pilot study

The purpose of this study was to evaluate the efficacy of a web-based cognitive rehabilitation intervention in survivors of adult-onset cancer and a sample of non-cancer community dwelling adults. Fifty-one participants were recruited and allocated to a cancer intervention group, a non-cancer intervention group, or a non-cancer waitlist group. Intervention groups completed a 4-week online program and all participants were assessed at baseline, post-intervention and 3-month follow-up. The primary outcome measure was subjective cognitive functioning. Secondary outcome measures included objective cognitive functioning, distress, quality of life (QoL), illness perception and program satisfaction. Results from the study found significant improvements on self-report measures of cognitive functioning in both treatment groups, as well as improvements on objective measures assessing attention and executive functioning. No intervention effects were observed for distress, QoL or illness perception. High participant satisfaction was observed with 75% of participants in the cancer group reporting being either "satisfied" or "very satisfied" with the program compared to 87% in the non-cancer treatment group. Initial evaluation of the program suggests that the web-based cognitive rehabilitation intervention shows potential for improving subjective and objective cognitive functioning in cancer survivors and community dwelling adults.

Muscle fatigue and excitation-contraction coupling responses following a session of prolonged cycling

AIM

The mechanisms underlying the fatigue that occurs in human muscle following sustained activity are thought to reside in one or more of the excitation-contraction coupling (E-C coupling) processes. This study investigated the association between the changes in select E-C coupling properties and the impairment in force generation that occurs with prolonged cycling.

METHODS

Ten volunteers with a peak aerobic power (VO(2peak)) of 2.95 ± 0.27 L min(-1) (mean ± SE), exercised for 2 h at 62 ± 1.3%. Quadriceps function was assessed and tissue properties (vastus lateralis) were measured prior to (E1-pre) and following (E1-post) exercise and on three consecutive days of recovery (R1, R2 and R3).

RESULTS

While exercise failed to depress the maximal activity (V(max) ) of the Na(+) ,K(+) -ATPase (P = 0.10), reductions (P < 0.05) were found at E1-post in V(max) of sarcoplasmic reticulum Ca(2+) -ATPase (-22%), Ca(2+) -uptake (-26%) and phase 1(-33%) and 2 (-38%) Ca(2+) -release. Both V(max) and Ca(2+) -release (phase 2) recovered by R1, whereas Ca(2+) -uptake and Ca(2+) -release (phase 1) remained depressed (P < 0.05) at R1 and at R1 and R2 and possibly R3 (P < 0.06) respectively. Compared with E1-pre, fatigue was observed (P < 0.05) at 10 Hz electrical stimulation at E1-post (-56%), which persisted throughout recovery. The exercise increased (P < 0.05) overall content of the Na(+), K(+)-ATPase (R1, R2 and R3) and the isoforms β2 (R1, R2 and R3) and β3 (R3), but not β1 or the α-isoforms (α1, α2 and α3).

CONCLUSION

These results suggest a possible direct role for Ca(2+)-release in fatigue and demonstrate a single exercise session can induce overlapping perturbations and adaptations (particularly to the Na(+), K(+)-ATPase).

Metabolic adaptations of oxidative muscle during spawning migration in the Atlantic salmon Salmo salar L

The adaptability/plasticity of the highly oxidative red muscle in Atlantic salmon was demonstrated during spawning migration. Substrate concentrations and the enzymatic pathways of ATP production were examined in red muscle obtained from Atlantic salmon at different sites along their migratory route in the Exploits River, Newfoundland, Canada. Individuals were chronologically sampled from a seawater site, two sites upstream, and at spawning. The 20% decrease in salmon body weight during the later stages of migration was accompanied by large decreases (mg dry weight(-1)) in both glycogen (P < 0.01) and total muscle lipid (P < 0.01). In contrast, water content and protein concentration (mg dry weight(-1)) of the red muscle increased by 25 and 34%, respectively, at spawning. Enzymes of the glycolytic pathways demonstrated a significant (P < 0.001) decrease in maximal activity as migration proceeded whereas enzymes of the oxidative phosphorylation pathways, specifically the citric acid cycle enzymes, exhibited an increase (P < 0.001) in maximal activity at spawning. The antioxidant enzyme superoxide dismutase also demonstrated an increase (P < 0.001) in maximal activity during the latter stages of migration. These adaptations imply that the red epaxial muscle of Atlantic salmon has a more efficient means of oxidizing lipids, while minimizing free radical damage, during the later stages of migration and spawning, thereby potentially increasing post spawning survival.

Time-dependent effects of short-term training on muscle metabolism during the early phase of exercise

In this study, we investigated the hypothesis that the metabolic adaptations observed during steady-state exercise soon after the onset of training would be displayed during the nonsteady period of moderate exercise and would occur in the absence of increases in peak aerobic power (Vo2peak) and in muscle oxidative potential. Nine untrained males [age = 20.8 +/- 0.70 (SE) yr] performed a cycle task at 62% Vo2peak before (Pre-T) and after (Post-T) training for 2 h/day for 5 days at task intensity. Tissue samples extracted from the vastus lateralis at 0 min (before exercise) and at 10, 60, and 180 s of exercise, indicated that at Pre-T, reductions (P < 0.05) in phosphocreatine and increases (P < 0.05) in creatine, inorganic phosphate, calculated free ADP, and free AMP occurred at 60 and 180 s but not at 10 s. At Post-T, the concentrations of all metabolites were blunted (P < 0.05) at 60 s. Training also reduced (P < 0.05) the increase in lactate and the lactate-to-pyruvate ratio observed during exercise at Pre-T. These adaptations occurred in the absence of change in Vo2peak (47.8 +/- 1.7 vs. 49.2 +/- 1.7 mlxkg(-1)xmin(-1)) and in the activities (molxkg protein(-1)xh(-1)) of succinic dehydrogenase (3.48 +/- 0.21 vs. 3.77 +/- 0.35) and citrate synthase (7.48 +/- 0.61 vs. 8.52 +/- 0.65) but not cytochrome oxidase (70.8 +/- 5.1 vs. 79.6 +/- 6.6 U/g protein; P < 0.05). It is concluded that the tighter metabolic control observed following short-term training is initially expressed during the nonsteady state, probably as a result of increases in oxidative phosphorylation that is not dependent on changes in Vo2peak while the role of oxidative potential remains uncertain.

Failure of hypoxia to exaggerate the metabolic stress in working muscle following short-term training

This study investigated the effects of hypoxia (experiment 1) and the effects of hypoxia following short-term training (experiment 2) on metabolism in working muscle. In experiment 1, eight males with a peak aerobic power (VO2peak) of 45 +/- 1.7 ml x kg(-1) x min(-1) (x +/- SE) cycled for 15 min at 66.1 +/- 2.1% VO2peak while breathing room air [normoxia (N)] or 14% O(2) [hypoxia (H)]. In experiment 2, nine males with a VO2peak of 43.3 +/- 1.6 ml x kg(-1) x min(-1) performed a similar protocol at 60.7 +/- 1.4% VO2peak during N and during H following 5 days of submaximal exercise training (H + T). Tissue samples extracted from the vastus lateralis before exercise and at 1, 3, and 15 min of exercise indicated that compared with N, H resulted in lower (P < 0.05) concentrations (mmol/kg dry wt) of creatine phosphate and higher (P < 0.05) concentrations of creatine, inorganic phosphate, and lactate, regardless of exercise time. When the exercise was performed at H + T and compared with N, no differences were observed in creatine phosphate, creatine, inorganic phosphate, and lactate, regardless of duration. Given the well-documented effects of the short-term training model on elevating VO2 kinetics and attenuating the alterations in high-energy phosphate metabolism and lactate accumulation, it would appear that the mechanism underlying the reversal of these adaptations during H is linked to a more rapid increase in oxidative phosphorylation, mediated by increased oxygen delivery and/or mitochondrial activation.

Abnormal sarcoplasmic reticulum Ca2+-sequestering properties in skeletal muscle in chronic obstructive pulmonary disease

The objective of this study was to investigate the hypothesis that alterations in sarcoplasmic reticulum (SR) Ca2+-cycling properties would occur in skeletal muscle in patients with moderate to severe chronic obstructive pulmonary disease (COPD). To investigate this hypothesis, tissue samples were obtained from the vastus lateralis of 8 patients with COPD [age 65.6 ± 3.2 yr; forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) = 44 ± 2%; mean ± SE] and 10 healthy age-matched controls (CON, age 67.5 ± 2.5 yr; FEV1/FVC = 77 ± 2%), and homogenates were analyzed for a wide range of SR properties. Compared with CON, COPD displayed (in μmol·g protein−1·min−1) a 16% lower maximal Ca2+-ATPase activity [maximal velocity ( Vmax), 158 ± 10 vs. 133 ± 7, P < 0.05] and a 17% lower Ca2+uptake (4.65 ± 0.039 vs. 3.85 ± 0.26, P < 0.05) that occurred in the absence of differences in Ca2+release. The lower Vmaxin COPD was also accompanied by an 11% lower ( P < 0.05) Ca2+sensitivity, as measured by the Hill coefficient (defined as the relationship between Ca2+-ATPase activity and free cytosolic Ca2+concentration for 10–90% Vmax). For the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) isoforms, SERCA1a was 16% higher ( P < 0.05) and SERCA2a was 14% lower ( P < 0.05) in COPD. It is concluded that moderate to severe COPD results in abnormalities in SR Ca2+-ATPase properties that cannot be explained by changes in the SERCA isoform phenotypes. The reduced catalytic properties of SERCA in COPD suggest a disturbance in Ca2+cycling, possibly resulting in impairment in Ca2+-mediated mechanical function and/or second messenger regulated processes.

Altered metabolic and transporter characteristics of vastus lateralis in chronic obstructive pulmonary disease

To investigate energy metabolic and transporter characteristics in resting muscle of patients with moderate to severe chronic obstructive pulmonary disease [COPD; forced expiratory volume in 1 s (FEV(1)) = 42 +/- 6.0% (mean +/- SE)], tissue was extracted from resting vastus lateralis (VL) of 9 COPD patients and compared with that of 12 healthy control subjects (FEV(1) = 114 +/- 3.4%). Compared with controls, lower (P < 0.05) concentrations (mmol/kg dry wt) of ATP (19.6 +/- 0.65 vs. 17.8 +/- 0.69) and phosphocreatine (81.3 +/- 2.3 vs. 69.1 +/- 4.2) were observed in COPD, which occurred in the absence of differences in the total adenine nucleotide and total creatine pools. Higher concentrations were observed in COPD for several glycolytic metabolites (glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, pyruvate) but not lactate. Glycogen storage was not affected by the disease (289 +/- 20 vs. 269 +/- 20 mmol glucosyl units/kg dry wt). Although no difference between groups was observed for the glucose transporter GLUT1, GLUT4 was reduced by 28% in COPD. For the monocarboxylate transporters, MCT4 was 35% lower in COPD, with no differences observed for MCT1. These results indicate that in resting VL, moderate to severe COPD results in a reduction in phosphorylation potential, an apparent elevation of glycolytic flux rate, and a potential defect in glucose and lactate transport as a result of reduced levels of the principal isoforms.

Dissociation between changes in muscle Na+-K+-ATPase isoform abundance and activity with consecutive days of exercise and recovery

The early plasticity of vastus lateralis Na(+)-K(+)-ATPase to the abrupt onset of prolonged submaximal cycling was studied in 12 untrained participants (Vo(2 peak) 44.8 +/- 2.0 ml x kg(-1) x min(-1), mean +/- SE) using a 6-day protocol (3 days of exercise plus 3 days of recovery). Tissue samples were extracted prior to (Pre) and following exercise (Post) on day 1 (E1) and day 3 (E3) and on each day of recovery (R1, R2, R3) and analyzed for changes in maximal protein (beta(max)) (vanadate-facilitated [(3)H]ouabain binding), alpha- and beta-isoform concentration (quantitative immunoblotting) and maximal Na(+)-K(+)-ATPase activity (V(max)) (3-O-methylfluorescein K(+)-stimulated phosphatase assay). For beta(max) (pmol/g wet wt), an increase (P < 0.05) of 11.8% was observed at R1 compared with E1-Pre (340 +/- 14 vs 304 +/- 17). For the alpha-isoforms alpha(1), alpha(2), and alpha(3), increases (P < 0.05) of 46, 42, and 31% were observed at R1, respectively. For the beta-isoform, beta(1) and beta(2) increased (P < 0.05) by 19 and 28% at R1, whereas beta(3) increased (P < 0.05) by 18% at R2. With the exception of alpha(2) and alpha(3), the increases in the isoforms persisted at R3. Exercise resulted in an average decrease (P < 0.05) in V(max) by 14.3%. No differences were observed in V(max) at E1 - Pre and E3 - Pre or between R1, R2, and R3. It is concluded that 3 days of prolonged exercise is a powerful stimulus for the rapid upregulation of the Na(+)-K(+)-ATPase subunit isoforms. Contrary to our hypothesis, the increase in subunit expression is not accompanied by increases in the maximal catalytic activity.

Acute responses in muscle mitochondrial and cytosolic enzyme activities during heavy intermittent exercise

To examine the effects of repetitive bouts of heavy exercise on the maximal activities of enzymes representative of the major metabolic pathways and segments, 13 untrained volunteers [peak aerobic power (V̇o2 peak) = 44.3 ± 2.3 ml·kg−1·min−1] cycled at ∼91% V̇o2 peak for 6 min once per hour for 16 h. Maximal enzyme activities ( Vmax, mol·kg−1·protein·h−1) were measured in homogenates from tissue extracted from the vastus lateralis before and after exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). For the mitochondrial enzymes, exercise resulted in reductions ( P < 0.05) in cytochrome- c oxidase (COX, 14.6%), near significant reductions in malate dehydrogenase (4.06%; P = 0.06) and succinic dehydrogenase (4.82%; P = 0.09), near significant increases in β-hydroxyacyl-CoA dehydrogenase (4.94%; P = 0.08), and no change in citrate synthase (CS, 2.88%; P = 0.37). For the cytosolic enzymes, exercise reduced ( P < 0.05) Vmax in hexokinase (Hex, 4.4%), creatine phosphokinase (9.0%), total phosphorylase (13.5%), phosphofructokinase (16.6%), pyruvate kinase (PK, 14.1%) and lactate dehydrogenase (10.7%). Repetition-dependent reductions ( P < 0.05) in Vmax were observed for CS (R1, R2 > R16), COX (R1, R2 > R16), Hex (1R, 2R > R16), and PK (R9 > R16). It is concluded that heavy exercise results in transient reductions in a wide range of enzymes involved in different metabolic functions and that in the case of selected enzymes, multiple repetitions of the exercise reduce average Vmax.

Rapid upregulation of GLUT-4 and MCT-4 expression during 16 h of heavy intermittent cycle exercise

In this study, we have investigated the hypothesis that an exercise protocol designed to repeatedly induce a large dependence on carbohydrate and large increases in glycolytic flux rate would result in rapid increases in the principal glucose and lactate transporters in working muscle, glucose transporter (GLUT)-4 and monocarboxylate transporter (MCT)4, respectively, and in activity of hexokinase (Hex), the enzyme used to phosphorylate glucose. Transporter abundance and Hex activity were assessed in homogenates by Western blotting and quantitative chemiluminescence and fluorometric techniques, respectively, in samples of tissue obtained from the vastus lateralis in 12 untrained volunteers [peak aerobic power (V̇o2peak) = 44.3 ± 2.3 ml·kg−1·min−1] before cycle exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). The 16 repetitions of the exercise were performed for 6 min at ∼90% V̇o2peak, once per hour. Compared with R1, GLUT-4 increased ( P < 0.05) by 28% at R2 and remained elevated ( P < 0.05) at R9 and R16. For MCT-4, increases ( P < 0.05) of 24% were first observed at R9 and persisted at R16. No changes were observed in GLUT-1 and MCT-1 or in Hex activity. The ∼17- to 24-fold increase ( P < 0.05) in muscle lactate observed at R1 and R2 was reduced ( P < 0.05) to an 11-fold increase at R9 and R16. It is concluded that an exercise protocol designed to strain muscle carbohydrate reserves and to result in large increases in lactic acid results in a rapid upregulation of both GLUT-4 and MCT-4.

Muscle metabolic, SR Ca2+-cycling responses to prolonged cycling, with and without glucose supplementation

This study investigated the effects of prolonged exercise, with and without glucose supplementation, on metabolism and sarcoplasmic reticulum (SR) Ca2+-handling properties in working vastus lateralis muscle. Fifteen untrained volunteers [peak O2consumption (V̇o2peak) = 3.45 ± 0.17 l/min; mean ± SE] cycled at ∼60% V̇o2peakon two occasions, during which they were provided with either an artificially sweetened placebo beverage (NG) or a 6% glucose (G) beverage (∼1.00 g carbohydrate/kg body mass). Beverage supplementation started at 30 min of exercise and continued every 15 min thereafter. SR Ca2+handling, metabolic, and substrate responses were assessed in tissue extracted from the vastus lateralis at rest, after 30 min and 90 min of exercise, and at fatigue in both conditions. Plasma glucose during G was 15–23% higher ( P < 0.05) than those observed during NG following 60 min of exercise until fatigue. Cycle time to fatigue was increased ( P < 0.05) by ∼19% during G (137 ± 7 min) compared with NG (115 ± 6 min). Prolonged exercise reduced ( P < 0.05) maximal Ca2+-ATPase activity (−18.4%), SR Ca2+uptake (−27%), and both Phase 1 (−22.2%) and Phase 2 (−34.2%) Ca2+-release rates during NG. The exercise-induced reductions in SR Ca2+-cycling properties were not altered during G. The metabolic responses to exercise were all unaltered by glucose supplementation, since no differences in respiratory exchange ratios, carbohydrate and lipid oxidation rates, and muscle metabolite and glycogen contents were observed between NG and G. These results indicate that the maintenance of blood glucose homeostasis by glucose supplementation is without effect in modifying the muscle metabolic, endogenous glycogen, or SR Ca2+-handling responses.

Muscle metabolic responses during 16 hours of intermittent heavy exercise

The alterations in muscle metabolism were investigated in response to repeated sessions of heavy intermittent exercise performed over 16 h. Tissue samples were extracted from the vastus lateralis muscle before (B) and after (A) 6 min of cycling at approximately 91% peak aerobic power at repetitions one (R1), two (R2), nine (R9), and sixteen (R16) in 13 untrained volunteers (peak aerobic power = 44.3 +/- 0.66 mL.kg-1.min-1, mean +/- SE). Metabolite content (mmol.(kg dry mass)-1) in homogenates at R1 indicated decreases (p < 0.05) in ATP (21.9 +/- 0.62 vs. 17.7 +/- 0.68) and phosphocreatine (80.3 +/- 2.0 vs. 8.56 +/- 1.5) and increases (p < 0.05) in inosine monophosphate (IMP, 0.077 +/- 0.12 vs. 3.63 +/- 0.85) and lactate (3.80 +/- 0.57 vs. 84.6 +/- 10.3). The content (micromol.(kg dry mass)-1) of calculated free ADP ([ADPf], 86.4 +/- 5.5 vs. 1014 +/- 237) and free AMP ([AMPf], 0.32 +/- 0.03 vs. 78.4 +/- 31) also increased (p < 0.05). No differences were observed between R1 and R2. By R9 and continuing to R16, pronounced reductions (p < 0.05) at A were observed in IMP (72.2%), [ADPf] (58.7%), [AMPf] (85.5%), and lactate (41.3%). The 16-hour protocol resulted in an 89.7% depletion (p < 0.05) of muscle glycogen. Repetition-dependent increases were also observed in oxygen consumption during exercise. It is concluded that repetitive heavy exercise results in less of a disturbance in phosphorylation potential, possibly as a result of increased mitochondrial respiration during the rest-to-work non-steady-state transition.

Muscle Na+-K+-ATPase response during 16 h of heavy intermittent cycle exercise

This study investigated the effects of a 16-h protocol of heavy intermittent exercise on the intrinsic activity and protein and isoform content of skeletal muscle Na(+)-K(+)-ATPase. The protocol consisted of 6 min of exercise performed once per hour at approximately 91% peak aerobic power (Vo(2 peak)) with tissue sampling from vastus lateralis before (B) and immediately after repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). Eleven untrained volunteers with a Vo(2 peak) of 44.3 +/- 2.3 ml x kg(-1) x min(-1) participated in the study. Maximal Na(+)-K(+)-ATPase activity (V(max), in nmol x mg protein(-1) x h(-1)) as measured by the 3-O-methylfluorescein K(+)-stimulated phosphatase assay was reduced (P < 0.05) by approximately 15% with exercise regardless of the number of repetitions performed. In addition, V(max) at R9 and R16 was lower (P < 0.05) than at R1 and R2. Vanadate-facilitated [(3)H]ouabain determination of Na(+)-K(+)-ATPase content (maximum binding capacity, pmol/g wet wt), although unaltered by exercise, increased (P < 0.05) 8.3% by R9 with no further increase observed at R16. Assessment of relative changes in isoform abundance measured at B as determined by quantitative immunoblotting showed a 26% increase (P < 0.05) in the alpha(2)-isoform by R2 and a 29% increase in alpha(3) by R9. At R16, beta(3) was lower (P < 0.05) than at R2 and R9. No changes were observed in alpha(1), beta(1), or beta(2). It is concluded that repeated sessions of heavy exercise, although resulting in increases in the alpha(2)- and alpha(3)-isoforms and decreases in beta(3)-isoform, also result in depression in maximal catalytic activity.

Muscle sarcoplasmic reticulum calcium regulation in humans during consecutive days of exercise and recovery

The study investigated the hypothesis that three consecutive days of prolonged cycle exercise would result in a sustained reduction in the Ca(2+)-cycling properties of the vastus lateralis in the absence of changes in the sarcoplasmic (endoplasmic) reticulum Ca(2+)-ATPase (SERCA) protein. Tissue samples were obtained at preexercise (Pre) and postexercise (Post) on day 1 (E1) and day 3 (E3) and during recovery day 1 (R1), day 2 (R2), and day 3 (R3) in 12 active but untrained volunteers (age 19.2 +/- 0.27 yr; mean +/- SE) and analyzed for changes (nmol.mg protein(-1).min(-1)) in maximal Ca(2+)-ATPase activity (V(max)), Ca(2+) uptake and Ca(2+) release (phase 1 and phase 2), and SERCA isoform expression (SERCA1a and SERCA2a). At E1, reductions (P < 0.05) from Pre to Post in V(max) (150 +/- 7 vs. 121 +/- 7), Ca(2+) uptake (7.79 +/- 0.28 vs. 5.71 +/- 0.33), and both phases of Ca(2+) release (phase 1, 20.3 +/- 1.3 vs. 15.2 +/- 1.1; phase 2, 7.70 +/- 0.60 vs. 4.99 +/- 0.48) were found. In contrast to V(max), which recovered at Pre E3 and then remained stable at Post E3 and throughout recovery, Ca(2+) uptake remained depressed (P < 0.05) at E3 Pre and Post and at R1 as did phase 2 of Ca(2+) release. Exercise resulted in an increase (P < 0.05) in SERCA1a (14% at R2) but not SERCA2a. It is concluded that rapidly adapting mechanisms protect V(max) following the onset of regular exercise but not Ca(2+) uptake and Ca(2+) release.

Glucose supplements increase human muscle in vitro Na+-K+-ATPase activity during prolonged exercise

Regulation of maximal Na+-K+-ATPase activity in vastus lateralis muscle was investigated in response to prolonged exercise with (G) and without (NG) oral glucose supplements. Fifteen untrained volunteers (14 males and 1 female) with a peak aerobic power (V̇o2peak) of 44.8 ± 1.9 ml·kg−1·min−1; mean ± SE cycled at ∼57% V̇o2peak to fatigue during both NG (artificial sweeteners) and G (6.13 ± 0.09% glucose) in randomized order. Consumption of beverage began at 30 min and continued every 15 min until fatigue. Time to fatigue was increased ( P < 0.05) in G compared with NG (137 ± 7 vs. 115 ± 6 min). Maximal Na+-K+-ATPase activity (Vmax) as measured by the 3- O-methylfluorescein phosphatase assay (nmol·mg−1·h−1) was not different between conditions prior to exercise (85.2 ± 3.3 or 86.0 ± 3.9), at 30 min (91.4 ± 4.7 vs. 91.9 ± 4.1) and at fatigue (92.8 ± 4.3 vs. 100 ± 5.0) but was higher ( P < 0.05) in G at 90 min (86.7 ± 4.2 vs. 109 ± 4.1). Na+-K+-ATPase content (βmax) measured by the vanadate facilitated [3H]ouabain-binding technique (pmol/g wet wt) although elevated ( P < 0.05) by exercise (0<30, 90, and fatigue) was not different between NG and G. At 60 and 90 min of exercise, blood glucose was higher ( P < 0.05) in G compared with NG. The G condition also resulted in higher ( P < 0.05) serum insulin at similar time points to glucose and lower ( P < 0.05) plasma epinephrine and norepinephrine at 90 min of exercise and at fatigue. These results suggest that G results in an increase in Vmax by mechanisms that are unclear.

Protection of muscle membrane excitability during prolonged cycle exercise with glucose supplementation

To determine if exercise-induced depressions in neuromuscular function are altered with oral glucose supplementation, 15 untrained participants (Vo2 peak = 45 +/- 2 ml x kg(-1) x min(-1), mean +/- SE) performed prolonged cycle exercise at approximately 60% Vo2 peak on two occasions: without glucose supplementation (NG) and with oral glucose supplementation (G). The oral G began at 30 min of exercise and was administered every 15 min (total ingested = 1.23 +/- 0.11 g carbohydrate/kg body mass). Quadriceps isometric properties and membrane excitability were assessed prior to exercise, after 90 min of exercise, and at fatigue. Cycle time to fatigue was greater (P < 0.05) in G compared with NG (137 +/- 7 vs. 115 +/- 6 min). Progressive reductions (P < 0.05) in maximal voluntary contraction (MVC, N) were observed for NG at 90 min (441 +/- 29) and at fatigue (344 +/- 33) compared with pre-exercise (666 +/- 30). At fatigue in G, the reduction in MVC was not as pronounced (P < 0.05) as in NG. Motor unit activation assessed with the interpolated twitch technique during an MVC following exercise was not different between conditions. During cycling, the G condition also resulted in a higher (P < 0.05) muscle compound potential (M-wave) amplitude (mV) at both 90 min (+50%) and at fatigue (+87%) compared with NG. Similar effects were also found M-wave area (mV/ms). These results suggest that the ergogenic effect of glucose supplementation occurs not as a result of decreased neural activation but to improved muscle function, possibly as a consequence of protection of muscle membrane excitability.

Comparative effects of a low-carbohydrate diet and exercise plus a low-carbohydrate diet on muscle sarcoplasmic reticulum responses in males

We employed a glycogen-depleting session of exercise followed by a low-carbohydrate (CHO) diet to investigate modifications that occur in muscle sarcoplasmic reticulum (SR) Ca2+-cycling properties compared with low-CHO diet alone. SR properties were assessed in nine untrained males [peak aerobic power (V̇o2 peak) = 43.6 ± 2.6 (SE) ml·kg−1·min−1] during prolonged cycle exercise to fatigue performed at ∼58% V̇o2 peakafter 4 days of low-CHO diet (Lo CHO) and after glycogen-depleting exercise plus 4 days of low-CHO (Ex+Lo CHO). Compared with Lo CHO, Ex+Lo CHO resulted in 12% lower ( P < 0.05) resting maximal Ca2+-ATPase activity ( Vmax= 174 ± 12 vs. 153 ± 10 μmol·g protein−1·min−1) and smaller reduction in Vmaxinduced during exercise. A similar effect was observed for Ca2+uptake. The Hill coefficient, defined as slope of the relationship between cytosolic free Ca2+concentration and Ca2+-ATPase activity, was higher ( P < 0.05) at rest (2.07 ± 0.15 vs. 1.90 ± 0.10) with Ex+Lo CHO, an effect that persisted throughout the exercise. The coupling ratio, defined as the ratio of Ca2+uptake to Vmax, was 23–30% elevated ( P < 0.05) at rest and during the first 60 min of exercise with Ex+Lo CHO. The ∼27 and 34% reductions ( P < 0.05) in phase 1 and phase 2 Ca2+release, respectively, observed during exercise with Lo CHO were not altered by Ex+Lo CHO. These results indicate that when prolonged exercise precedes a short-term Lo CHO diet, Ca2+sequestration properties and efficiency are improved compared with those during Lo CHO alone.

Effects of prior exercise and a low-carbohydrate diet on muscle sarcoplasmic reticulum function during cycling in women

The effects of exercise and diet on sarcoplasmic reticulum Ca(2+)-cycling properties in female vastus lateralis muscle were investigated in two groups of women following four different conditions. The conditions were 4 days of a low-carbohydrate (Lo CHO) and glycogen-depleting exercise plus a Lo CHO diet (Ex + Lo CHO) (experiment 2) and 4 days of normal CHO (Norm CHO) and glycogen-depleting exercise plus Norm CHO (Ex + Norm CHO) (experiment 1). Peak aerobic power (Vo2peak)) was 38.1 +/- 1.4 (SE); n = 9 and 35.6 +/- 1.4 ml.kg(-1).min(-1); n = 9, respectively. Sarcoplasmic reticulum properties measured in vitro in homogenates (micromol.g protein(-1).min(-1)) indicated exercise-induced reductions (P < 0.05) in maximal Ca(2+)-ATPase activity (0 > 30, 60 min > fatigue), Ca(2+) uptake (0 > 30 > 60 min, fatigue), and Ca(2+) release, both phase 1 (0, 30 > 60 min, fatigue) and phase 2 (0 > 30, 60 min, fatigue; 30 min > fatigue) in Norm CHO. Exercise was without effect in altering the Hill slope (n(H)), defined as the slope of relationship between Ca(2+)-ATPase activity and Ca(2+) concentration. No differences were observed between Norm CHO and Ex+Norm CHO. Compared with Norm CHO, Lo CHO resulted in a lower (P < 0.05) Ca(2+) uptake, phase 1 Ca(2+) release (30 min), and n(H). Ex + Lo CHO resulted in a greater (P < 0.05) Ca(2+) uptake and n(H) compared with Lo CHO. The results demonstrate that Lo CHO alone can disrupt SR Ca(2+) cycling and that, with the exception of Ca(2+) release, a glycogen-depleting session of exercise before Lo CHO can reverse the effects.

Manipulation of dietary carbohydrates after prolonged effort modifies muscle sarcoplasmic reticulum responses in exercising males

The hypothesis tested was that disturbances in the sarcoplasmic reticulum (SR) Ca2+-cycling responses to exercise would associate with muscle glycogen reserves. Ten untrained males [peak O2 consumption (VO2 peak) = 3.41 +/- 0.20 (SE) l/min] performed a standardized cycle test (approximately 70% VO2 peak) on two occasions, namely, following 4 days of a high (Hi CHO)- and 4 days of a low (Lo CHO)-carbohydrate diet. Both Hi CHO and Lo CHO were preceded by a session of prolonged exercise designed to deplete muscle glycogen. SR Ca2+ cycling in crude homogenates prepared from vastus lateralis samples indicated higher (P < 0.05) Ca2+ uptake (microM x g protein(-1) x min(-1)) in Hi CHO compared with Lo CHO at 30 min (2.93 +/- 0.10 vs. 2.23 +/- 0.12) and at 67 min (2.77 +/- 0.16 vs. 2.10 +/- 0.12) of exercise, the point of fatigue in Lo CHO. Similar effects (P < 0.05) were noted between conditions for maximal Ca2+-ATPase (microM x g protein(-1) x min(-1)) at 30 min (142 +/- 8.5 vs. 107 +/- 5.0) and at 67 min (130 +/- 4.5 vs. 101 +/- 4.7). Both phase 1 and phase 2 Ca2+ release were 23 and 37% higher (P < 0.05) at 30 min of exercise and 15 and 34% higher (P < 0.05), at 67 min during Hi CHO compared with Lo CHO, respectively. No differences between conditions were observed at rest for any of these SR properties. Total muscle glycogen (mmol glucosyl units/kg dry wt) was higher (P < 0.05) in Hi CHO compared with Lo CHO at rest (+36%), 30 min (+53%), and at 67 min (+44%) of cycling. These results indicate that exercise-induced reductions in SR Ca2+-cycling properties occur earlier in exercise during low glycogen states compared with high glycogen states.

Oxidative stress and nitric oxide synthase in skeletal muscles of rats with post-infarction, compensated chronic heart failure

AIM

Involvement of oxidative stress and nitric oxide synthase (NOS) isoforms in skeletal muscle cellular adaptations to chronic heart failure (CHF) is controversial, and possible muscle fibre-type heterogeneity in the oxidative stress and NOS responses to CHF have not been examined. Consequently, we hypothesized that the changes in determinants of elevated oxidative and nitrosylative stress associated with CHF would occur in skeletal muscle and would be similar in predominantly type I slow twitch muscle (soleus) and type II fast twitch muscle (plantaris) of rats.

METHODS

The purpose of this study was to measure NOS isoforms (endothelial, inducible and neuronal NOS) and antioxidant enzymes (SOD-1, SOD-2, catalase) by protein immunoblot as well as markers of oxidative stress by biochemical assays in soleus and plantaris muscle sections of the rat hind limb. This was performed for control and post-infarction, compensated CHF rats.

RESULTS

Twelve weeks after coronary artery ligation-induced moderate CHF, soleus exhibited decreased SOD-1, SOD-2 and eNOS, but increased iNOS and nNOS isoforms assessed by immunoblot. This was associated with elevated lipid and DNA oxidative damage assessed by biochemical assays. In contrast, plantaris muscle exhibited no changes in antioxidant enzymes or NOS isoforms, and had lower lipid and DNA oxidative damage.

CONCLUSION

These observations suggest a heretofore unreported muscle fibre-type-specific response of oxidative stress and NOS isoforms to CHF is of importance in understanding the cellular mechanisms of skeletal muscle dysfunction in CHF.

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.

Mechanisms underlying increases in rat soleus Na+-K+-ATPase activity by induced contractions

Acute regulation of the Na(+)-K(+)-ATPase activity in rat soleus muscle was investigated in response to 15 and 90 min of electrically induced contractile activity (500-ms trains at 30 Hz every 1.5 s). Kinetic measurements of Na(+)-K(+)-ATPase activity, assessed by the 3-O-methylfluorescein K(+)-stimulated phosphatase assay (3-O-MFP), were performed on crude homogenates (Hom) and on tissue separated into two membrane fractions, the sarcolemmal/particulate (SLP) and endosomal (En), in both stimulated (Stim) and contralateral control (Con) muscles. Maximal 3-O-MFP activity (V(max), nmol.mg protein(-1).h(-1)) was elevated (P < 0.05) in Stim by 40% and by 53% in Hom and by 37 and 40% in SLP at 15 and 90 min, respectively. The 38% increase (P < 0.05) in the alpha(2)-isoform subunit distribution in SLP at 15 min, as assessed by quantitative immunoblotting, persisted at 90 min, whereas for En a 42% decrease (P < 0.05) was observed only at 15 min. For the alpha(1)-subunit at 15 min, a 27% decrease (P < 0.05) was observed in En, whereas the 13% increase observed in SLP was not significant (P = 0.08). At 90 min, alpha(1) was increased (P < 0.05) by 14% in SLP and by 29% in En. No changes were observed in beta(1)-subunit distribution in En and SLP regardless of time of stimulation. Immunoprecipitation with antiphosphotyrosine antibody and quantitative immunoblotting with alpha(1)- and alpha(2)-antibodies indicated increases (P < 0.05) in tyrosine phosphorylation of 51% in alpha(2) at 15 min only. These results suggest that the increases in V(max) during contractile activity are mediated both by increased phosphorylation and by translocation of the enzyme to the plasma membrane.

Muscle Na-K-pump and fatigue responses to progressive exercise in normoxia and hypoxia

To investigate the effects of hypoxia and incremental exercise on muscle contractility, membrane excitability, and maximal Na+-K+-ATPase activity, 10 untrained volunteers (age = 20 ± 0.37 yr and weight = 80.0 ± 3.54 kg; ± SE) performed progressive cycle exercise to fatigue on two occasions: while breathing normal room air (Norm; FiO2= 0.21) and while breathing a normobaric hypoxic gas mixture (Hypox; FiO2= 0.14). Muscle samples extracted from the vastus lateralis before exercise and at fatigue were analyzed for maximal Na+-K+-ATPase (K+-stimulated 3-O-methylfluorescein phosphatase) activity in homogenates. A 32% reduction ( P < 0.05) in Na+-K+-ATPase activity was observed (90.9 ± 7.6 vs. 62.1 ± 6.4 nmol·mg protein−1·h−1) in Norm. At fatigue, the reductions in Hypox were not different (81 ± 5.6 vs. 57.2 ± 7.5 nmol·mg protein−1·h−1) from Norm. Measurement of quadriceps neuromuscular function, assessed before and after exercise, indicated a generalized reduction ( P < 0.05) in maximal voluntary contractile force (MVC) and in force elicited at all frequencies of stimulation (10, 20, 30, 50, and 100 Hz). In general, no differences were observed between Norm and Hypox. The properties of the compound action potential, amplitude, duration, and area, which represent the electomyographic response to a single, supramaximal stimulus, were not altered by exercise or oxygen condition when assessed both during and after the progressive cycle task. Progressive exercise, conducted in Hypox, results in an inhibition of Na+-K+-ATPase activity and reductions in MVC and force at different frequencies of stimulation; these results are not different from those observed with Norm. These changes occur in the absence of reductions in neuromuscular excitability.

Metabolic and sarcoplasmic reticulum Ca2+cycling responses in human muscle 4 days following prolonged exercise

This study investigated the effects of prolonged exercise on muscle sarcoplasmic reticulum (SR) Ca2+cycling properties and the metabolic responses with and without a session of exercise designed to reduce muscle glycogen reserves while on a normal carbohydrate (CHO) diet. Eight untrained males (VO2peak = 3.81 ± 0.12 L/min, mean ± SE) performed a standardized cycle-to-fatigue at 55% VO2peakwhile on a normal CHO diet (Norm CHO) and 4 days following prolonged exercise while on a normal CHO diet (Ex+Norm CHO). Compared to rest, exercise in Norm CHO to fatigue resulted in significant reductions (p < 0.05) in Ca2+uptake (3.17 ± 0.21 vs. 2.47 ± 0.12 µmol·(g protein)–1·min–1), maximal Ca2+ATPase activity (Vmax, 152 ± 12 vs. 119 ± 9 µmol·(g protein)–1·min–1) and both phase 1 (15.1 ± 0.98 vs. 13.1 ± 0.28 µmol·(g protein)–1·min–1) and phase 2 (6.56 ± 0.33 vs. 4.91 ± 0.28 µmol·(g protein)–1·min–1) Ca2+release in vastus lateralis muscle. No differences were observed between Norm CHO and Ex-Norm CHO in the response of these properties to exercise. Compared with Norm CHO, Ex+Norm CHO resulted in higher (p < 0.05) resting Ca2+uptake (3.17 ± 0.21 vs. 3.49 ± 0.24 µmol·(g protein)·min–1and higher ionophore ratio, defined as the ratio of Vmaxmeasured with and without the Ca2+-ionophore A23187, (2.3 ± 0.3 vs. 4.4 ± 0.3 µmol·(g protein)·min–1) at fatigue. No differences were observed between conditions in the concentration of muscle glycogen, the high-energy phosphates (ATP and PCr), or metabolites (Pi, Cr, and lactate). Ex+Norm CHO also failed to modify the exercise-induced changes in CHO and fat oxidation. We conclude that prolonged exercise to fatigue performed 4 days following glycogen-depleting exercise while on a normal CHO diet elevates resting Ca2+uptake and prevents increases in SR membrane permeability to Ca2+as measured by the ionophore ratio. Key words: Ca2+cycling, glycogen depletion, contractile activity, recovery.

Muscle sarcoplasmic reticulum Ca2+ cycling adaptations during 16 h of heavy intermittent cycle exercise

The repetition-dependent effects of a repetitive heavy exercise protocol previously shown to alter muscle mechanic behavior (Green HJ, Duhamel TA, Ferth S, Holloway GP, Thomas MM, Tupling AR, Rich SM, and Yau JE. J Appl Physiol 97: 2166-2175, 2004) on muscle sarcoplasmic reticulum (SR) Ca2+-transport properties, measured in vitro, were examined in 12 untrained volunteers [peak aerobic power (VO2(peak)) = 44.3 +/- 0.66 ml x kg(-1) x min(-1)]. The protocol involved 6 min of cycle exercise performed at approximately 91% VO2(peak) once per hour for 16 h. Tissue samples were obtained from the vastus lateralis before (B) and after (A) exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). Reductions (P < 0.05) in maximal Ca2+-ATPase activity (Vmax) of 26 and 12% with exercise were only observed at R1 and R16, respectively. Vmax remained depressed (P < 0.05) at R2 (B) but not at R9 (B) and R16 (B). No changes were observed in two other kinetic properties of the enzyme, namely the Hill coefficient (defined as the slope of the relationship between Ca2+-ATPase activity and free Ca2+ concentration) and the Ca50 (defined as the free Ca2+ concentration needed to elicit 50% Vmax). Changes in Ca2+ uptake (measured at 2,000 nM) with exercise and recovery generally paralleled Vmax. The apparent coupling ratio, defined as the ratio between Ca2+ uptake and Vmax, was unaffected by the intermittent protocol. Reductions (P < 0.05) in phase 1 Ca2+ release (32%) were only observed at R1. No differences were observed between B and A for R2, R9, and R16 or between B and B for R1, R2, R9, and R16. The changes in phase 2 Ca2+ release were as observed for phase 1 Ca2+ release. It is concluded that the SR Ca2+-handling properties, in general, display rapid adaptations to repetitive exercise.

Na+-K+-ATPase properties in rat heart and skeletal muscle 3 mo after coronary artery ligation

This study was designed to determine whether chronic heart failure (CHF) results in changes in Na(+)-K(+)-ATPase properties in heart and skeletal muscles of different fiber-type composition. Adult rats were randomly assigned to a control (Con; n = 8) or CHF (n = 8) group. CHF was induced by ligation of the left main coronary artery. Examination of Na(+)-K(+)-ATPase activity (means +/- SE) 12 wk after the ligation measured, using the 3-O-methylfluorescein phosphatase assay (3-O-MFPase), indicated higher (P < 0.05) levels in soleus (Sol) (250 +/- 13 vs. 179 +/- 18 nmol.mg protein(-1).h(-1)) and lower (P < 0.05) levels in diaphragm (Dia) (200 +/- 12 vs. 272 +/- 27 nmol.mg protein(-1).h(-1)) and left ventricle (LV) (760 +/- 62 vs. 992 +/- 16 nmol.mg protein(-1).h(-1)) in CHF compared with Con, respectively. Na(+)-K(+)-ATPase protein content, measured by the [(3)H]ouabain binding technique, was higher (P < 0.05) in white gastrocnemius (WG) (166 +/- 12 vs. 135 +/- 7.6 pmol/g wet wt) and lower (P < 0.05) in Sol (193 +/- 20 vs. 260 +/- 8.6 pmol/g wet wt) and LV (159 +/- 10 vs. 221 +/- 10 pmol/g wet wt) in CHF compared with Con, respectively. Isoform content in CHF, measured by Western blot techniques, showed both increases (WG; P < 0.05) and decreases (Sol; P < 0.05) in alpha(1). For alpha(2), only increases [red gastrocnemius (RG), Sol, and Dia; P < 0.05] occurred. The beta(2)-isoform was decreased (LV, Sol, RG, and WG; P < 0.05) in CHF, whereas the beta(1) was both increased (WG and Dia; P < 0.05) and decreased (Sol and LV; P < 0.05). For beta(3), decreases (P < 0.05) in RG were observed in CHF, whereas no differences were found in Sol and WG between CHF and Con. It is concluded that CHF results in alterations in Na(+)-K(+)-ATPase that are muscle specific and property specific. Although decreases in Na(+)-K(+)-ATPase content would appear to explain the lower 3-O-MFPase in the LV, such does not appear to be the case in skeletal muscles where a dissociation between these properties was observed.

Reversal of muscle fatigue during 16 h of heavy intermittent cycle exercise

This study examined the effects of extended sessions of heavy intermittent exercise on quadriceps muscle fatigue and weakness. Twelve untrained volunteers (10 men and 2 women), with a peak oxygen consumption of 44.3 ± 2.3 ml·kg−1·min−1, exercised at ∼91% peak oxygen consumption for 6 min once per hour for 16 h. Muscle isometric properties assessed before and after selected repetitions (R1, R2, R4, R7, R12, and R15) were used to quantitate fatigue (before vs. after repetitions) and weakness (before vs. before repetitions). Muscle fatigue at R1 was indicated by reductions ( P < 0.05) in peak twitch force (135 ± 13 vs. 106 ± 11 N) and by a reduction ( P < 0.05) in the force-frequency response, which ranged between ∼53% at 10 Hz (113 ± 12 vs. 52.6 ± 7.4 N) and ∼17% at 50 Hz (324 ± 27 vs. 270 ± 30 N). No recovery of force, regardless of stimulation frequency, was observed during the 54 min between R1 and R2. At R2 and for all subsequent repetitions, no reduction in force, regardless of stimulation frequency, was generally found after the exercise. The only exception was for R2, where, at 20 Hz, force was reduced ( P < 0.05) by 18%. At R15, force before repetitions for high frequencies (i.e., 100 Hz) returned to R1 (333 ± 29 vs. 324 ± 27 N), whereas force at low frequency (i.e., 10 Hz) was only partially ( P < 0.05) recovered (113 ± 12 vs. 70 ± 6.6 N). It is concluded that multiple sessions of heavy exercise can reverse the fatigue noted early and reduce or eliminate weakness depending on the frequency of stimulation.

Human muscle sarcoplasmic reticulum function during submaximal exercise in normoxia and hypoxia

In this study, the response of the sarcoplasmic reticulum (SR) to prolonged exercise, performed in normoxia (inspired O2fraction = 0.21) and hypoxia (inspired O2fraction = 0.14) was studied in homogenates prepared from the vastus lateralis muscle in 10 untrained men (peak O2consumption = 3.09 ± 0.25 l/min). In normoxia, performed at 48 ± 2.2% peak O2consumption, maximal Ca2+-dependent ATPase activity was reduced by ∼25% at 30 min of exercise compared with rest (168 ± 10 vs. 126 ± 8 μmol·g protein−1·min−1), with no further reductions observed at 90 min (129 ± 6 μmol·g protein−1·min−1). No changes were observed in the Hill coefficient or in the Ca2+concentration at half-maximal activity. The reduction in maximal Ca2+-dependent ATPase activity at 30 min of exercise was accompanied by oxalate-dependent reductions ( P < 0.05) in Ca2+uptake by ∼20% (370 ± 22 vs. 298 ± 25 μmol·g protein−1·min−1). Ca2+release, induced by 4-chloro- m-cresol and assessed into fast and slow phases, was decreased ( P < 0.05) by ∼16 and ∼32%, respectively, by 90 min of exercise. No differences were found between normoxia and hypoxia for any of the SR properties examined. It is concluded that the disturbances induced in SR Ca2+cycling with prolonged moderate-intensity exercise in human muscle during normoxia are not modified when the exercise is performed in hypoxia.

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.

Malleability of human skeletal muscle Na+-K+-ATPase pump with short-term training

To investigate the hypothesis that short-term submaximal training would result in changes in Na+-K+-ATPase content, activity, and isoform distribution in skeletal muscle, seven healthy, untrained men [peak aerobic power (peak oxygen consumption; V̇o2 peak) = 45.6 ml·kg−1·min−1 (SE 5.4)] cycled for 2 h/day at 60–65% V̇o2 peak for 6 days. Muscle tissue, sampled from the vastus lateralis before training (0 days) and after 3 and 6 days of training and analyzed for Na+-K+-ATPase content, as assessed by the vanadate facilitated [3H]ouabain-binding technique, was increased ( P < 0.05) at 3 days (294 ± 8.6 pmol/g wet wt) and 6 days (308 ± 15 pmol/g wet wt) of training compared with 0 days (272 ± 9.7 pmol/g wet wt). Maximal Na+-K+-ATPase activity as evaluated by the 3- O-methylfluorescein phosphatase assay was increased ( P < 0.05) by 6 days (53.4 ± 5.9 nmol·h−1·mg protein−1) but not by 3 days (35.9 ± 4.5 nmol·h−1·mg protein−1) compared with 0 days (37.8 ± 3.7 nmol·h−1·mg protein−1) of training. Relative isoform distribution, measured by Western blot techniques, indicated increases ( P < 0.05) in α2-content by 3 days and β1-content by 6 days of training. These results indicate that prolonged aerobic exercise represents a potent stimulus for the rapid adaptation of Na+-K+-ATPase content, isoform, and activity characteristics.

Quality of life compared during pharmacological treatments and clinical monitoring for non-localized prostate cancer: a randomized controlled trial

OBJECTIVES

To investigate the effects of different management strategies for non-localized prostate cancer on men's quality of life and cognitive functioning.

PATIENTS, SUBJECTS AND METHODS

Men with prostate cancer were randomly assigned to one of four treatment arms: leuprorelin, goserelin, cyproterone acetate (CPA), or close clinical monitoring. In a repeated-measures design, men were assessed before treatment (baseline) and after 6 and 12 months of treatment. A community comparison group of men of the same age with no prostate cancer participated for the same length of time. The men were recruited from public and private urology departments from university teaching hospitals. All those with prostate cancer who were eligible for hormonal therapy had no symptoms requiring immediate therapy. In all, 82 patients were randomized and 62 completed the 1-year study, and of the 20 community participants, 15 completed the study. The main outcome measures were obtained from questionnaires on emotional distress, existential satisfaction, physical function and symptoms, social and role function, subjective cognitive function, and sexual function, combined with standard neuropsychological tests of memory, attention, and executive functions.

RESULTS

Sexual dysfunction increased for patients on androgen-suppressing therapies, and emotional distress increased in those assigned to CPA or close clinical monitoring. Compared with before treatment there was evidence of an adverse effect of leuprorelin, goserelin, and CPA on cognitive function.

CONCLUSIONS

In deciding the timing of androgen suppression therapy for prostate cancer, consideration should be given to potential adverse effects on quality of life and cognitive function.

Effects of prolonged exercise and recovery on sarcoplasmic reticulum Ca2+ cycling properties in rat muscle homogenates

AIM

To examine the effects of exercise and exercise plus active and passive recovery on sarcoplasmic reticulum (SR) Ca2+-handling properties.

METHODS

Crude muscle homogenates were prepared from adult rat gastrocnemius muscle from two experiments. In one experiment, the muscle was extracted immediately after prolonged treadmill running (RUN), after a 45 min period of reduced exercise intensity (RUN+) following RUN and compared with controls (CON). In the second experiment, muscle was extracted during passive recovery following the same run protocol at 10 min (REC10), 25 min (REC25) and 45 min (REC45) and compared with CON.

RESULTS

Sarcoplasmic reticulum Ca2+-uptake was 31% higher (P < 0.05) in RUN+ compared with CON and RUN. Higher values (P < 0.05) were also found in REC25 (48%) and REC45 (50%) compared with CON. Maximal Ca2+-ATPase was increased by 23% (P < 0.05) in RUN+ compared with CON and RUN and by 65-68% (P < 0.05) in REC25 and REC45 compared with CON. A higher (P < 0.05) Hill coefficient for Ca2+-ATPase activity was observed in RUN+ (2.3 +/- 0.2) compared with CON (1.7 +/- 0.2) or RUN (1.6 +/- 0.2), but not for any REC conditions. In addition, the coupling ratio (Ca2+-uptake/Ca2+-ATPase activity) was higher (P < 0.05) in RUN+ (2.2 +/- 0.10) compared with CON (1.9 +/- 0.05) and RUN (1.9 +/- 0.08).

CONCLUSIONS

It is concluded that in crude homogenates, SR Ca2+-uptake and Ca2+-ATPase activity are elevated in recovery following prolonged running and that the elevation in these properties is more pronounced during passive compared with active recovery.

Inactivation of human muscle Na+-K+-ATPase in vitro during prolonged exercise is increased with hypoxia

This study investigated the effects of prolonged exercise performed in normoxia (N) and hypoxia (H) on neuromuscular fatigue, membrane excitability, and Na+-K+-ATPase activity in working muscle. Ten untrained volunteers [peak oxygen consumption (VV̇o2 peak) = 42.1 ± 2.8 (SE) ml·kg-1·min-1] performed 90 min of cycling during N (inspired oxygen fraction = 0.21) and during H (inspired oxygen fraction = 0.14) at ∼50% of normoxic VV̇o2 peak. During N, 3- O-methylfluorescein phosphatase activity (nmol·mg protein-1·h-1) in vastus lateralis, used as a measure of Na+-K+-ATPase activity, decreased ( P < 0.05) by 21% at 30 min of exercise compared with rest (101 ± 53 vs. 79.6 ± 4.3) with no further reductions observed at 90 min (72.8 ± 8.0). During H, similar reductions ( P < 0.05) were observed during the first 30 min (90.8 ± 5.3 vs. 79.0 ± 6.3) followed by further reductions ( P < 0.05) at 90 min (50.5 ± 3.9). Exercise in N resulted in reductions ( P < 0.05) in both quadriceps maximal voluntary contractile force (MVC; 633 ± 50 vs. 477 ± 67 N) and force at low frequencies of stimulation, namely 10 Hz (142 ± 16 vs. 86.7 ± 10 N) and 20 Hz (283 ± 32 vs. 236 ± 31 N). No changes were observed in the amplitude, duration, and area of the muscle compound action potential (M wave). Exercise in H was without additional effect in altering MVC, low-frequency force, and M-wave properties. It is concluded that, although exercise in H resulted in a greater inactivation of Na+-K+-ATPase activity compared with N, neuromuscular fatigue and membrane excitability are not differentially altered.

Na+-K+-ATPase in rat skeletal muscle: content, isoform, and activity characteristics

The purpose of this study was to investigate the hypothesis that muscle Na+-K+-ATPase activity is directly related to Na+-K+-ATPase content and the content of the alpha2-catalytic isoform in muscles of different fiber-type composition. To investigate this hypothesis, tissue was sampled from soleus (Sol), red gastrocnemius (RG), white gastrocnemius (WG), and extensor digitorum longus (EDL) muscles at rest from 38 male Wistar rats weighing 413 +/- 6.0 g (mean +/- SE). Na+-K+-ATPase activity was determined in homogenates (Hom) and isolated crude membranes (CM) by the regenerating ouabain-inhibitable hydrolytic activity assay (ATPase) and the 3-O-methylfluorescein K+-stimulated phosphatase (3-O-MFPase) assay in vitro. In addition, Na+-K+-ATPase content (Bmax) and the distribution of alpha1-, alpha2-, beta1-, and beta2-isoforms were determined by [3H]ouabain binding and Western blot, respectively. For the ATPase assay, differences (P < 0.05) in enzyme activity between muscles were observed in Hom (EDL > WG) and in CM (Sol > EDL = WG). For the 3-O-MFPase assay, differences (P < 0.05) were also found for Hom (Sol > RG = EDL > WG) and CM (Sol = WG > RG). For Bmax, differences in the order of RG = EDL > Sol = WG (P < 0.05) were observed. Isoform distribution was similar between Hom and CM and indicated in CM, a greater density (P < 0.05) of alpha1 in Sol than WG and EDL (P < 0.05), but more equal distribution of alpha2 between muscles. The beta1 was greater (P < 0.05) in Sol and RG, and the beta2 was greater in EDL and WG (P < 0.05). Over all muscles, the correlation (r) between Hom 3-O-MFPase and Bmax was 0.45 (P < 0.05) and between Hom alpha2 and Bmax, 0.59 (P < 0.05). The alpha1 distribution correlated to Hom 3-O-MFPase (r = 0.79, P < 0.05) CM ATPase (r = 0.69, P < 0.005) and CM 3-O-MFPase activity (r = 0.32, P < 0.05). The alpha2 distribution was not correlated with any of the Na+-K+-ATPase activity measurements. The results indicate generally poor relationships between activity and total pump content and alpha2 isoform content of the Na+-K+-ATPase. Several factors, including the type of preparation and the type of assay, appear important in this regard.

Coexistence of potentiation and low-frequency fatigue during voluntary exercise in human skeletal muscle

The role of muscle potentiation in overcoming low-frequency fatigue (LFF) as it developed during submaximal voluntary exercise was investigated in eight males (age 26.4 ± 0.7 years, mean ± SE) performing isometric leg extension at ~30% of maximal voluntary contraction for 60 min using a 0.5-duty cycle (1 s contraction, 1 s rest). At 5, 20, 40, and 60 min, exercise was interrupted for 3 min, and the maximum positive rate of force development (+dF/dtmax) and maximal twitch force (Pt) were measured in maximal twitch contractions at 0, 1, 2, and 3 min of rest (R0, R1, R2, R3); they were also measured at 15 min of recovery following the entire 60-min exercise period. These measures were compared with pre-exercise (PRE) as an indicator of potentiation. Force at low frequency (10 Hz) was also measured at R0, R1, R2, and R3, and at 15 min of recovery, while force at high frequency (100 Hz) was measured only at R0 and R3 and in recovery. Voluntary exercise increased twitch +dF/dtmax at R0 following 5, 20, 40, and 60 min of exercise, from 2553 ± 150 N/s at PRE to 39%, 41%, 42%, and 36% above PRE, respectively (P < 0.005). Twitch +dF/dtmax decayed at brief rest (R3) following 20, 40, and 60 min of exercise (P < 0.05). Pt at R0 following 5 and 20 min of exercise was above that at PRE (P < 0.05), indicating that during the early phase of moderate- intensity repetitive exercise, potentiation occurs in the relative absence of LFF. At 40 and 60 min of exercise, Pt at R0 was unchanged from PRE. The LFF (10 Hz) induced by the protocol was evident at 40 and 60 min (R0–R3; P < 0.05) and at 15 min following exercise (P < 0.05). High-frequency force was not significantly compromised by the protocol. Since twitch force was maintained, these results suggest that as exercise progresses, LFF develops, which can be compensated for by potentiation.Key words: excitability, myosin light chain, phosphorylation, isometric exercise.

Paradoxical effects of prior activity on human sarcoplasmic reticulum Ca2+-ATPase response to exercise

To investigate the effects of intermittent heavy exercise (HE) on sarcoplasmic reticulum (SR) maximal Ca2+-ATPase activity (Vmax) and Ca2+ uptake, a continuous two-stage standardized cycling test was performed before and after HE by untrained men [peak aerobic power (Vo -->Vo2 peak) = 42.9 +/- 2.7 ml. kg-1 x min-1]. The HE consisted of 16 bouts of cycling performed for 6 min each hour at 90% Vo2 peak. Tissue was obtained from the vastus lateralis by needle biopsy before and during each cycle test. Before HE, reductions (P < 0.05 micromol. g protein-1x min-1) of 16 and 31% were observed in Vmax and Ca2+ uptake, respectively, after 40 min of the standardized test. Resting Vmax and Ca2+ uptake were depressed (P < 0.05) by 19 and 30%, respectively, when measured 36-48 h after HE. During the standardized test, after HE, Vmax increased (P < 0.05) by 20%, whereas no change was observed in Ca2+ uptake. The HE protocol resulted in small increases (P < 0.05) and decreases (P < 0.05) in sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) 2a and SERCA1 expression, respectively, as determined by Western blotting techniques. These results indicate that SR Ca2+-sequestering function in response to a prolonged exercise test depends on prior activity status, such that rested muscles exhibit a decrease and prior exercised muscles, an increase in Ca2+-ATPase activity. Moreover, it appears that changes in SERCA content can occur in response to a sustained session of intermittent exercise.

Adaptations in human muscle sarcoplasmic reticulum to prolonged submaximal training

In this study, we employed single-leg submaximal cycle training, conducted over a 10-wk period, to investigate adaptations in sarcoplasmic reticulum (SR) Ca(2+)-regulatory proteins and processes of the vastus lateralis. During the final weeks, the untrained volunteers (age 21.4 +/- 0.3 yr; means +/- SE, n = 10) were exercising 5 times/wk and for 60 min/session. Analyses were performed on tissue extracted by needle biopsy approximately 4 days after the last training session. Compared with the control leg, the trained leg displayed a 19% reduction (P < 0.05) in homogenate maximal Ca(2+)-ATPase activity (192 +/- 11 vs. 156 +/- 18 micromol. g protein(-1). min(-1)), a 4.3% increase (P < 0.05) in pCa(50), defined as the Ca(2+) concentration at half-maximal activity (6.01 +/- 0.05 vs. 6.26 +/- 0.07), and no change in the Hill coefficient (1.75 +/- 0.15 vs. 1.76 +/- 0.21). Western blot analysis using monoclonal antibodies (7E6 and A52) revealed a 13% lower (P < 0.05) sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) 1 in trained vs. control in the absence of differences in SERCA2a. Training also resulted in an 18% lower (P < 0.05) SR Ca(2+) uptake and a 26% lower (P < 0.05) Ca(2+) release. It is concluded that a downregulation in SR Ca(2+) cycling in vastus lateralis occurs with aerobic-based training, which at least in the case of Ca(2+) uptake can be explained by reduction in Ca(2+)-ATPase activity and SERCA1 protein levels.

Mechanisms underlying increases in SR Ca2+-ATPase activity after exercise in rat skeletal muscle

Prolonged exercise followed by a brief period of reduced activity has been shown to result in an overshoot in maximal sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity [maximal velocity (V(max))] in rat locomoter muscles (Ferrington DA, Reijneveld JC, Bär PR, and Bigelow DJ. Biochim Biophys Acta 1279: 203-213, 1996). To investigate the functional significance and underlying mechanisms for the increase in V(max), we analyzed Ca(2+)-ATPase activity and Ca(2+) uptake in SR vesicles from the fast rat gastrocnemius muscles after prolonged running (RUN) and after prolonged running plus 45 min of low-intensity activity (RUN+) or no activity (REC45) and compared them with controls (Con). Although no differences were observed between RUN and Con, both V(max) and Ca(2+) uptake were higher (P < 0.05) by 43 and 63%, respectively, in RUN+ and by 35 and 34%, respectively, in REC45. The increase in V(max) was accompanied by increases (P < 0.05) in the phosphorylated enzyme intermediate measured by [gamma-(32)P]ATP. No differences between groups for each condition were found for the fluorescent probes FITC and (N-cyclohexyl-N(1)-dimethylamino-alpha-naphthyl)carbodiimide, competitive inhibitors of the nucleotide-binding and Ca(2+)-binding sites on the enzyme, respectively. Similarly, no differences for the Ca(2+)-ATPase were observed between groups in nitrotyrosine and phosphoserine residues, a measure of nitrosylation and phosphorylation states, respectively. Western blots indicated no changes in relative isoform content of sarcoendoplasmic reticulum (SERCA)1 and SERCA2a. It is concluded that the increase in V(max) of the Ca(2+)-ATPase observed in recovery is not the result of changes in enzyme nitroslyation or phosphorylation, changes in ATP and Ca(2+)-binding affinity, or changes in protein content of the Ca(2+)-ATPase.

Na+,K+-ATPase concentration and fiber type distribution after spinal cord injury

Complete spinal cord injury (SCI) is characterized, in part, by reduced fatigue-resistance of the paralyzed skeletal muscle during stimulated contractions, but the underlying mechanisms are not fully understood. The effects of complete SCI on skeletal muscle Na(+),K(+)-adenosine triphosphatase (ATPase) concentration, and fiber type distribution were therefore investigated. Six individuals (aged 32.0 +/- 5.3 years) with complete paraplegia (T4-T10; 1-19 years since injury) participated. There was a significantly lower Na(+),K(+)-ATPase concentration in the paralyzed vastus lateralis (VL) when compared to either the subjects' own unaffected deltoid or literature values (from our laboratory, utilizing the same methodology) of VL Na(+),K(+)-ATPase concentration for the healthy able-bodied (141.6 +/- 50.0, 213.4 +/- 23.9, 339 +/- 16 pmol/g wet wt., respectively; P < 0.05). There was also a significant negative correlation between the Na(+),K(+)-ATPase concentration in the paralyzed VL and years since injury (r = -0.75, P < 0.05). These findings are clinically relevant as they suggest that reductions in Na(+),K(+)-ATPase contribute to the fatigability of paralyzed muscle after SCI. Unexpectedly, the VL muscles of our subjects had a higher proportion of their area represented by type I fibers compared to literature values for the VL of the healthy able-bodied (52.6 +/- 25.3% vs. 36 +/- 11.3%, respectively; P < 0.05). As all our subjects had upper motor neuron injuries and, therefore, experienced muscle spasticity, our findings warrant further investigation into the relationship between muscle spasticity and fiber type expression after SCI.

Reduced activity of muscle Na(+)-K(+)-ATPase after prolonged running in rats

The purpose of this study was to investigate the hypothesis that Na(+)-K(+)-ATPase activity is reduced in muscle of different fiber composition after a single session of aerobic exercise in rats. In one experiment, untrained female Sprague-Dawley rats (weight 275 +/- 21 g; means +/- SE; n = 30) were run (Run) on a treadmill at 21 m/min and 8% grade until fatigue, or to a maximum of 2 h, which served as control (Con), or performed an additional 45 min of low-intensity exercise at 10 m/min (Run+). In a second experiment, utilizing rats of similar characteristics (weight 258 +/- 18 g; n = 32), Run was followed by passive recovery (Rec). Directly after exercise, rats were anesthetized, and tissue was extracted from Soleus (Sol), red vastus lateralis (RV), white vastus lateralis (WV), and extensor digitorum longus (EDL) and frozen for later analysis. 3-O-methylfluorescein phosphatase activity (3-O-MFPase) was determined as an indicator of Na(+)-K(+)-ATPase activity, and glycogen depletion identified recruitment of each muscle during exercise. 3-O-MFPase was decreased (P < 0.05) at Run+ by an average of 12% from Con in all muscles (P < 0.05). No difference was found between Con and Run. Glycogen was lower (P < 0.05) by 65, 57, 44, and 33% (Sol, EDL, RV, and WV, respectively) at Run, and there was no further depletion during the continued low-intensity exercise period. No differences in Na(+)-K(+)-ATPase activity was observed between Con and Rec. The results of this study indicate that inactivation of Na(+)-K(+)-ATPase can be induced by aerobic exercise in a volume-dependent manner and that the inactivation that occurs is not specific to muscles of different fiber-type composition. Inactivation of Na(+)-K(+)-ATPase suggests intrinsic structural modifications by mechanisms that are unclear.

Thermal instability of rat muscle sarcoplasmic reticulum Ca(2+)-ATPase function

To examine the thermal instability and the role of sulfhydryl (SH) oxidation on sarcoplasmic reticulum (SR) Ca(2+)-ATPase function, crude homogenates were prepared from the white portion of the gastrocnemius (WG) adult rat muscles (n = 9) and incubated in vitro for < or =60 min either at a normal resting body temperature (37 degrees C) or at a temperature indicative of exercise-induced hyperthermia (41 degrees C) with DTT and without DTT (CON). In general, treatment with DTT resulted in higher Ca(2+)-ATPase and Ca(2+) uptake values (nmol. mg protein(-1). min(-1), P < 0.05), an effect that was not specific to time of incubation. Incubations at 41 degrees C resulted in lower (P < 0.05) Ca(2+) uptake rates (156 +/- 18 and 35.9 +/- 3.3) compared with 37 degrees C (570 +/- 54 and 364 +/- 26) at 30 and 60 min, respectively. At 37 degrees C, ryanodine (300 microM), which was used to block Ca(2+) release from the calcium release channel, prevented the time-dependent decrease in Ca(2+) uptake. A general inactivation (P < 0.05) of maximal Ca(2+)-ATPase activity (V(max)) in CON was observed with incubation time (0 > 30 > 60 min), with the effect being more pronounced (P < 0.05) at 41 degrees C compared with 37 degrees C. The Hill slope, a measure of co-operativity, and the pCa(50), the cytosolic Ca(2+) concentration required for half-maximal activation of Ca(2+)-ATPase activity, decreased (P < 0.05) at 41 degrees C only. Treatment with DTT attenuated the alterations in enzyme kinetics. The increase in V(max) with the Ca(2+) ionophore A-23187 was less pronounced at 41 degrees C compared with 37 degrees C. It is concluded that exposure of homogenates to a temperature typically experienced in exercise results in a reduction in the coupling ratio, which is mediated primarily by lower Ca(2+) uptake and occurs as a result of increases in membrane permeability to Ca(2+). Moreover, the decreases in Ca(2+)-ATPase kinetics in WG with sustained heat stress result from SH oxidation.

Altered cognitive function in men treated for prostate cancer with luteinizing hormone-releasing hormone analogues and cyproterone acetate: a randomized controlled trial

OBJECTIVE

To report the first systematic investigation of the cognitive effects of luteinizing hormone-releasing hormone (LHRH) analogues in male patients, as LHRH analogues have been associated with memory impairments in women using these drugs for gynaecological conditions.

PATIENTS AND METHODS

Eighty-two men with extraprostatic prostate cancer were randomly assigned to receive either continuous leuprorelin, goserelin (both LHRH analogues), cyproterone acetate (a steroidal antiandrogen) or close clinical monitoring. These patients underwent cognitive assessments at baseline and before starting treatment (77), and then 6 months later (65).

RESULTS

Compared with the baseline assessments, men receiving androgen suppression monotherapy performed worse in two of 12 tests of attention and memory; 24 of 50 men randomized to active treatment and assessed 6 months later had a clinically significant decline in one or more cognitive tests but not one patient randomized to close monitoring showed a decline in any test performance.

CONCLUSION

Pharmacological androgen suppression monotherapy for prostate cancer may be associated with impaired memory, attention and executive functions.

Human neuromuscular fatigue is associated with altered Na+-K+-ATPase activity following isometric exercise

The purpose of this study was to investigate the hypothesis that reductions in Na+-K+- ATPase activity are associated with neuromuscular fatigue following isometric exercise. In control (Con) and exercised (Ex) legs, force and electromyogram were measured in 14 volunteers [age, 23.4 +/- 0.7 (SE) yr] before and immediately after (PST0), 1 h after (PST1), and 4 h after (PST4) isometric, single-leg extension exercise at ~60% of maximal voluntary contraction for 30 min using a 0.5 duty cycle (5-s contraction, 5-s rest). Tissue was obtained from vastus lateralis muscle before exercise in Con and after exercise in both the Con (PST0) and Ex legs (PST0, PST1, PST4), for the measurements of Na+-K+-ATPase activity, as determined by the 3-O-methylfluorescein phosphatase (3-O-MFPase) assay. Voluntary (maximal voluntary contraction) and elicited (10, 20, 50, 100 Hz) force was reduced 30-55% (P < 0.05) at PST0 and did not recover by PST4. Muscle action potential (M-wave) amplitude and area (measured in the vastus medialis) and 3-O-MFPase activity at PST0-Ex were less than that at PST0-Con (P < 0.05) by 37, 25, and 38%, respectively. M-wave area at PST1-Ex was also less than that at PST1-Con (P < 0.05). Changes in 3-O-MFPase activity correlated to changes in M-wave area across all time points (r = 0.38, P < 0.05, n = 45). These results demonstrate that Na+-K+- ATPase activity is reduced by sustained isometric exercise in humans from that in a matched Con leg and that this reduction in Na+-K+-ATPase activity is associated with loss of excitability as indicated by M-wave alterations.

Substrate turnover and oxidation during moderate-intensity exercise following acute plasma volume expansion

In previous work using prolonged, light cycle exercise, we were unable to demonstrate an effect of acute plasma volume (PV) expansion on glucose kinetics or substrate oxidation, despite a decline in whole-body lipolysis (Phillips et al., 1997). However, PV is known to decrease arterial O2 content. The purpose of this study was to examine whether substrate turnover and oxidation would be altered with heavier exercise where the challenge to O2 delivery is increased. Eight untrained males (VO2max = 3.52 +/- 0.12 l/min) twice performed 90 min of cycle ergometry at 62 % VO2peak, both prior to (CON) and following induced plasma volume expansion (Dextran [6 %] or Pentaspan [10 %]) (6.7 ml/kg) (PVX). Glucose and glycerol kinetics were determined with primed constant infusions of [6.6-(2)H2] glucose and [(2)H5] glycerol, respectively. PVX resulted in a 15.8 +/- 2.2 % increase (p < 0.05) in PV. Glucose and glycerol appearance (Ra) and utilization (Rd), although increasing progressively (p < 0.05) with exercise, were not different between conditions. Similarly, no differences in substrate oxidation, either fat or carbohydrate, were observed between the two conditions. Prolonged exercise resulted in an increase (p < 0.05) in plasma glucagon and a decrease (p < 0.05) in plasma insulin during both conditions. With PVX, the exercise-induced increase in glucagon was diminished (p < 0.05). We conclude that impairment in O2 content mediated by an elevated PV does not alter glucose, and glycerol kinetics or substrate oxidation even at moderate exercise intensity.

Prolonged exercise following diuretic-induced hypohydration effects on fluid and electrolyte hormones

To investigate the hypothesis that a reduction in plasma volume (PV) induced by diuretic administration would result in an increase in the fluid and electrolyte hormonal response to exercise, ten untrained males (VO(2) peak = 3.96 +/- 0.14 l/min) performed 60 min of cycle ergometry at 61 % VO(2) peak twice. The test was carried out once under control conditions (CON) (placebo) and once after 4 days of diuretic administration (DIU) (Novotriamazide; 100 mg triamterene and 50 mg hydrochlorothiazide). Calculated resting PV decreased by 14.6 +/- 3.3 % (p < 0.05) with DIU. No difference in plasma osmolality was observed between conditions. For the hormones measured, differences (p < 0.05) between conditions at rest were noted for plasma renin activity (PRA) (0.62 +/- 0.09 vs. 5.61 +/- 0.94 ng/ml/h), angiotensin I (ANG 1) (0.26 +/- 0.03 vs. 0.56 +/- 0.08 ng/ml), aldosterone (ALD) (143 +/- 14 vs. 1603 +/- 302 pg/ml), arginine vasopressin (AVP) (4.13 +/- 1.1 vs. 9.58 +/- 1.6 pg/ml) and atrial natriuretic peptide (alpha-ANP) (11.5 +/- 2.8 vs. 6.33 +/- 1.0 pg/ml). The exercise resulted in increases (p < 0.05) in PRA, ANG I, ALD, AVP, alpha-ANP. DIU led to higher levels of PRA, ANG I, and ALD (p < 0.05) and lower levels of alpha-ANP (p < 0.05) compared to CON. Arginine vasopressin was not affected by the loss of PV. For the catecholamines--norepinephrine (NE) and epinephrine (EPI)--only NE was higher during exercise with DIU compared to CON (p < 0.05). For PRA and ALD, the higher levels observed during exercise with DIU could be explained both by higher resting levels and a greater increase during exercise itself. For ANG I and NE, the effect of DIU only manifested itself during exercise. In contrast, the lower alpha-ANP observed during exercise with DIU was due to the lower resting levels. These results support the hypotheses that hypohydration leads to alterations in the secretion of all of the fluid and electrolyte hormones with the exception of AVP. The specific mechanisms of these alterations remain unclear, but appear to be related directly to the decrease in PV.

Acute plasma volume expansion in the untrained alters the hormonal response to prolonged moderate-intensity exercise

To investigate the role of an increase in plasma volume (PV), characteristically observed with short-term endurance training, on the endocrine response to prolonged moderate intensity exercise, eight untrained males (VO2 peak = 3.52 +/- 0.12 l x min(-1)) performed 90 min of cycle ergometry at approximately 60% VO2peak both before (CON) and following (PVX) PV expansion. Acute PV expansion, which was accomplished using a solution of Dextran (6%) or Pentispan (10%) (6.7 ml kg(-1)), resulted in a calculated 15.8+/-2.2% increase (p<0.05) in PV. The prolonged exercise resulted in increases (p<0.05) in plasma vasopressin (AVP), plasma rennin activity (PRA), aldosterone (ALD), atrial naturetic peptide (alpha-ANP), and the catecholamines norepinephrine (NE) and epinephrine (EPI). PVX blunted the increases (p<0.05) in AVP, PRA, ALD, NE and EPI, during the exercise itself. The concentration of alpha-ANP was also lower (p<0.05) during exercise following PVX, an effect that could be attributed to the lower resting levels. No differences in osmolality was observed between conditions. These results demonstrate that PVX alters the fluid regulatory hormonal response in untrained subjects to moderate intensity dynamic exercise in a manner similar to that observed following short-term training induced alterations in PV. The specific mechanisms responsible for these alterations remain unclear, but appear to be related directly to the increase in PV.

Reduced oxygen uptake during steady state exercise after 21-day mountain climbing expedition to 6,194 m

We investigated the effect of a 21-day climbing expedition to 6,194 m on the oxygen uptake (V022) and leg blood flow (LBF) responses to submaximal exercise in five healthy, fit men during two-leg kicking exercise a 0-W and 50-W. Tests were completed 1 week before and 3 days after altitued acclimatization. The adaptation of VO2 at exercise onset was described by the time to 63% of the new steady state. Steady state VO2 during 50-W exercise was less post-climb (1290+/- 29 mL/min, mean +/- SE) than pre-climb (1413+/- 63 mL/min, P <.05). VO2 adapted more slowly at the onset of 50-W exercise post climb. There were no differences in the steady state LBF during the 50-W exercise, the increase above baseline, or the adaptation post-climb. Respiratory exchange ratio was greater at 50-W post-climb compared to pre-climb. Reduced steady state V02 during exercise after exposure to high altitude is consistent with an increase in metabolic efficiency.

Differences in skeletal muscle between men and women with chronic heart failure

Men with chronic heart failure (CHF) have alterations in their skeletal muscle that are partially responsible for a decreased exercise tolerance. The purpose of this study was to investigate whether skeletal muscle alterations in women with CHF are similar to those observed in men and if these alterations are related to exercise intolerance. Twenty-five men and thirteen women with CHF performed a maximal exercise test for evaluation of peak oxygen consumption (VO(2)) and resting left ventricular ejection fraction, after which a biopsy of the vastus lateralis was performed. Twenty-one normal subjects (11 women, 10 men) were also studied. The relationship between muscle markers and peak VO(2) was consistent for CHF men and women. When controlling for gender, analysis showed that oxidative enzymes and capillary density are the best predictors of peak VO(2.) These results indicate that aerobically matched CHF men and women have no differences in skeletal muscle biochemistry and histology. However, when CHF groups were separated by peak exercise capacity of 4.5 metabolic equivalents (METs), CHF men with peak VO(2) >4.5 METs had increased citrate synthase and 3-hydroxyacyl-CoA dehydrogenase compared with CHF men with peak VO(2) <4.5 METs. CHF men with a lower peak VO(2) had increased capillary density compared with men with higher peak VO(2). These observations were not reproduced in CHF women. This suggests that differences may exist in how skeletal muscle adapts to decreasing peak VO(2) in patients with CHF.

Normal skeletal muscle Na(+)-K(+) pump concentration in patients with chronic heart failure

Intrinsic changes in skeletal muscle are being increasingly suspected as part of the underlying cause of exercise intolerance in patients with chronic heart failure (CHF). The objective of the present study was to determine whether differences existed between CHF patients and age-matched healthy controls in the concentration of skeletal muscle Na(+)-K(+)-ATPase (adenosine triphosphatase), a cation pump that functions to restore Na(+)-K(+) gradients and protect membrane excitability. Moreover, given the potency for physical activity in altering long-term regulation of the pump, an additional objective was to examine the role of activity level in pump expression in CHF patients. Na(+)-K(+)-ATPase concentration (pmol/g wet wt) determined in the vastus lateralis muscle of 27 CHF males (ejection fraction, 23 +/- 1.6%), using the vanadate facilitated [(3)H] ouabain binding technique, was not different (264 +/- 10) from 10 sedentary controls (268 +/- 19,P > 0.05). Similarly, no differences (P > 0.05) could be found between female patients (228 +/- 16, n = 7) and controls (243 +/- 13, n = 9). Differences between untrained control (294 +/- 20, n = 7), chronically active (251 +/- 20, n = 9), and trained (252 +/- 16, n = 6) CHF groups in Na(+)-K(+) pump expression were also insignificant. This study indicates that long-term regulation of Na(+)-K(+)-ATPase concentration is not altered in moderate CHF patients, regardless of the history of regular activity. However, the positive correlations (P < 0.05) that were observed between peak aerobic power (VO(2) peak) and Na(+)-K(+)-ATPase (r = 0.422) and VO(2) peak and maximal citrate synthase activity (r = 0.404) suggests a role for the skeletal muscle in explaining exercise intolerance in CHF patients.