Effect of non-invasive ventilation on the measurement of ventilatory and metabolic variables.

The effect of non-invasive ventilation (NIV) on the accuracy of measurements of ventilation, oxygen consumption (V˙O2) and carbon dioxide production (V˙CO2) was examined using a simulator. Known gas volumes of oxygen and carbon dioxide were delivered to a metabolic system that measured tidal volume, respiratory rate, V˙O2 and V˙CO2, both with and without NIV. Bland-Altman analyses were used to compare between conditions. NIV at pressure support (PS) 20cm H2O compared to without NIV showed: VT, mean difference (MD) 0mL (limits of agreement (LOA) -21 to 21) mL; V˙O2 MD -413 (LOA -810 to 16) mL/min; and V˙CO2 MD 32 (LOA -32 to 97) mL/min. For V˙O2 measurements during NIV, a correction was applied to account for increased air density due to PS. After correction, V˙O2 measurement accuracy improved; MD -46 (LOA -108 to 17) mL/min. Tidal volume and metabolic variables can be measured with acceptable accuracy during NIV, providing V˙O2 is corrected for altered gas density.

The contribution of VEGF signalling to fostamatinib-induced blood pressure elevation.

BACKGROUND AND PURPOSE: Fostamatinib is an inhibitor of spleen tyrosine kinase (TK). In patients, fostamatinib treatment was associated with increased BP. Some TK inhibitors cause BP elevation, by inhibiting the VEGF receptor 2 (VEGFR2). Here, we have assessed the mechanistic link between fostamatinib-induced BP elevation and inhibition of VEGF signalling. EXPERIMENTAL APPROACH: We used conscious rats with automated blood sampling and radio telemetry and anaesthetized rats to measure cardiovascular changes. Rat isolated aorta and isolated hearts, and human resistance vessels in vitro were also used. NO production by human microvascular endothelial cells was measured with the NO-dependent probe, DAF-FM and VEGFR2 phosphorylation was determined in mouse lung, ex vivo. KEY RESULTS: In conscious rats, fostamatinib dose-dependently increased BP. The time course of the BP effect correlated closely with the plasma concentrations of R406 (the active metabolite of fostamatinib). In anaesthetized rats, infusion of R406 increased BP and decreased femoral arterial conductance. Endothelial function was unaffected, as infusion of R406 did not inhibit hyperaemia- or ACh-induced vasodilatation in rats. R406 did not affect contraction of isolated blood vessels. R406 inhibited VEGF-stimulated NO production from human endothelial cells in vitro, and treatment with R406 inhibited VEGFR2 phosphorylation in vivo. R406 inhibited VEGF-induced hypotension in anaesthetized rats. CONCLUSIONS AND IMPLICATIONS: Increased vascular resistance, secondary to reduced VEGF-induced NO release from endothelium, may contribute to BP increases observed with fostamatanib. This is consistent with the elevated BP induced by other drugs inhibiting VEGF signalling, although the contribution of other mechanisms cannot be excluded.

Effects of type 1 diabetes, sprint training and sex on skeletal muscle sarcoplasmic reticulum Ca2+ uptake and Ca2+-ATPase activity.

Calcium cycling is integral to muscle performance during the rapid muscle contraction and relaxation of high-intensity exercise. Ca(2+) handling is altered by diabetes mellitus, but has not previously been investigated in human skeletal muscle. We investigated effects of high-intensity exercise and sprint training on skeletal muscle Ca(2+) regulation among men and women with type 1 diabetes (T1D, n = 8, 3F, 5M) and matched non-diabetic controls (CON, n = 8, 3F, 5M). Secondarily, we examined sex differences in Ca(2+) regulation. Subjects undertook 7 weeks of three times-weekly cycle sprint training. Before and after training, performance was measured, and blood and muscle were sampled at rest and after high-intensity exercise. In T1D, higher Ca(2+)-ATPase activity (+28%) and Ca(2+) uptake (+21%) than in CON were evident across both times and days (P < 0.05), but performance was similar. In T1D, resting Ca(2+)-ATPase activity correlated with work performed until exhaustion (r = 0.7, P < 0.01). Ca(2+)-ATPase activity, but not Ca(2+) uptake, was lower (-24%, P < 0.05) among the women across both times and days. Intense exercise did not alter Ca(2+)-ATPase activity in T1D or CON. However, sex differences were evident: Ca(2+)-ATPase was reduced with exercise among men but increased among women across both days (time × sex interaction, P < 0.05). Sprint training reduced Ca(2+)-ATPase (-8%, P < 0.05), but not Ca(2+) uptake, in T1D and CON. In summary, skeletal muscle Ca(2+) resequestration capacity was increased in T1D, but performance was not greater than CON. Sprint training reduced Ca(2+)-ATPase in T1D and CON. Sex differences in Ca(2+)-ATPase activity were evident and may be linked with fibre type proportion differences.

Validation of an in vitro contractility assay using canine ventricular myocytes.

Measurement of cardiac contractility is a logical part of pre-clinical safety assessment in a drug discovery project, particularly if a risk has been identified or is suspected based on the primary- or non-target pharmacology. However, there are limited validated assays available that can be used to screen several compounds in order to identify and eliminate inotropic liability from a chemical series. We have therefore sought to develop an in vitro model with sufficient throughput for this purpose. Dog ventricular myocytes were isolated using a collagenase perfusion technique and placed in a perfused recording chamber on the stage of a microscope at ~36 °C. Myocytes were stimulated to contract at a pacing frequency of 1 Hz and a digital, cell geometry measurement system (IonOptix™) was used to measure sarcomere shortening in single myocytes. After perfusion with vehicle (0.1% DMSO), concentration-effect curves were constructed for each compound in 4-30 myocytes taken from 1 or 2 dog hearts. The validation test-set was 22 negative and 8 positive inotropes, and 21 inactive compounds, as defined by their effect in dog, cynolomolgous monkey or humans. By comparing the outcome of the assay to the known in vivo contractility effects, the assay sensitivity was 81%, specificity was 75%, and accuracy was 78%. With a throughput of 6-8 compounds/week from 1 cell isolation, this assay may be of value to drug discovery projects to screen for direct contractility effects and, if a hazard is identified, help identify inactive compounds.

On the relationship between block of the cardiac Na⁺ channel and drug-induced prolongation of the QRS complex.

BACKGROUND AND PURPOSE: Inhibition of the human cardiac Na(+) channel (hNa(v) 1.5) can prolong the QRS complex and has been associated with increased mortality in patients with underlying cardiovascular disease. The safety implications of blocking hNa(v) 1.5 channels suggest the need to test for this activity early in drug discovery in order to design out any potential liability. However, interpretation of hNa(v) 1.5 blocking potency requires knowledge of how hNa(v) 1.5 block translates into prolongation of the QRS complex. EXPERIMENTAL APPROACH: We tested Class I anti-arrhythmics, other known QRS prolonging drugs and drugs not reported to prolong the QRS complex. Their block of hNa(v) 1.5 channels (as IC(50) values) was measured in an automated electrophysiology-based assay. These IC(50) values were compared with published reports of the corresponding unbound (free) plasma concentrations attained during clinical use (fC(max)) to provide an IC(50) : fC(max) ratio. KEY RESULTS For 42 Class I anti-arrhythmics and other QRS prolonging drugs, 67% had IC(50) : fC(max) ratios <30. For 55 non-QRS prolonging drugs tested, 72% had ratios >100. Finally, we determined the relationship between the IC(50) value and the free drug concentration associated with prolongation of the QRS complex in humans. For 37 drugs, QRS complex prolongation was observed at free plasma concentrations that were about 15-fold lower than the corresponding IC(50) at hNa(v) 1.5 channels. CONCLUSIONS AND IMPLICATIONS: A margin of 30- to 100-fold between hNa(v) 1.5 IC(50) and fC(max) appears to confer an acceptable degree of safety from QRS prolongation. QRS prolongation occurs on average at free plasma levels 15-fold below the IC(50) at hNa(v) 1.5 channels. LINKED ARTICLE: This article is commented on by Gintant et al., pp. 254-259 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2011.01433.x.

Glucose tolerance and physical activity level in people with spinal cord injury.

STUDY DESIGN: Cross-sectional, observational study. OBJECTIVES: To evaluate the associations of physical activity and neurological lesion level with glucose tolerance in people with spinal cord injury (SCI). SETTING: New South Wales, Australia. METHODS: Twenty-five people (5 women, 20 men) with SCI (>6 months post-injury) aged between 18 and 65 years were recruited. Exclusion criteria included known coronary heart disease, stroke or diabetes. Participants underwent an oral glucose tolerance test. Fasting and 2-h plasma glucose concentrations were classified according to the World Health Organization categories of glycemia. Participants also completed the Physical Activity Scale for Individuals with Physical Disabilities and mean MET-hours day(-1) was calculated. Associations with the 2-h plasma glucose concentration were calculated through multiple and stepwise regressions. RESULTS: Participants presented with complete or incomplete tetraplegia (n=11 TETRA) or complete or incomplete paraplegia (n=14 PARA) with neurological lesion levels ranging from C3/4 to T12. Mean 2-h plasma glucose was 7.13+/-2.32 mmol l(-1). Nine participants had disordered glycemia (n=6 TETRA; n=3 PARA) and the remaining participants had normal glucose tolerance. Those participants with normal glucose tolerance participated in more moderate-vigorous and strength exercise and undertook more non-exercise-related mobility than those with disordered glycemia. Physical activity and age, but not lesion level were independent determinants of 2-h plasma glucose concentration (r=0.683, P=0.001), explaining 47% of the variance. CONCLUSION: Physical activity level is independently associated with glucose tolerance in people with SCI. Non-exercise activity may also be important for maintaining normal glycemia.

Fitness training for cardiorespiratory conditioning after traumatic brain injury.

BACKGROUND: Cardiorespiratory deconditioning is a common sequelae after traumatic brain injury (TBI). Clinically, fitness training is implemented to address this impairment, however this intervention has not been subject to rigorous review. OBJECTIVES: The primary objective was to evaluate whether fitness training improves cardiorespiratory fitness in people who have sustained a TBI. SEARCH STRATEGY: We searched ten electronic databases (Cochrane Injuries Group Trials Register; Cochrane Central Register of Controlled Trials (CENTRAL); EMBASE; PubMed (MEDLINE); CINAHL; AMED; SPORTDiscus; PsycINFO; PEDro and PsycBITE) and two clinical trials registers (TrialsCentral and Current Controlled Trials). The last search was August 2007. In addition we screened reference lists from included studies and contacted trialists to identify further studies. SELECTION CRITERIA: Randomised controlled studies with TBI participants were eligible if they compared an exercise programme incorporating cardiorespiratory fitness training to usual care, a non-exercise intervention or no intervention. DATA COLLECTION AND ANALYSIS: Two authors independently screened the search output, extracted data and assessed quality. All trialists were contacted for additional information. Mean difference and 95% confidence intervals (CI) were calculated for continuous data and risk difference or odds ratio and 95% CI were calculated for dichotomous data. Data were pooled when there were sufficient studies with clinical and statistical homogeneity. MAIN RESULTS: Six studies, incorporating 303 participants, were included. The participants were primarily males, in their mid thirties who had sustained a severe TBI. The studies were clinically diverse with regard to the interventions, time post-injury and the outcome measures used; therefore, the primary outcome could not be pooled. Three of the six studies indirectly assessed change in cardiorespiratory fitness after fitness training using the peak power output obtained during cycle ergometry (either at volitional fatigue or at a predetermined endpoint, that is, a percentage of predicted heart rate maximum). Cardiorespiratory fitness was improved after fitness training in one study (mean difference 59 watts, 95% CI 24 to 94), whilst there was no significant improvement in the other two studies. Four of the six studies had no drop-outs from their intervention group and no adverse events were reported in any study. AUTHORS' CONCLUSIONS: There is insufficient evidence to draw any definitive conclusions about the effects of fitness training on cardiorespiratory fitness. Whilst it appears to be a safe and accepted intervention for people with TBI, more adequately powered and well-designed studies are required to determine the effects across a range of outcome measures.

Optimisation and validation of a medium-throughput electrophysiology-based hNav1.5 assay using IonWorks.

INTRODUCTION: The safety implications of blocking the human cardiac Na(+) channel (hNav1.5) make it prudent to test for this activity early in the drug discovery process and design-out any potential liability. This needs a method with adequate throughput and a demonstrable predictive value to effects in native cardiac tissues. Here we describe the validation of a method that combines the ability to screen tens of compounds a day, with direct assessment of channel function. METHODS: The electrophysiological and pharmacological properties of hNav1.5 were compared using two methods: conventional, low-throughput electrophysiology and planar-array-based, medium-throughput electrophysiology (IonWorks HT). A pharmacological comparison was also made between IonWorks HT and canine cardiac Purkinje Fibre action potential upstroke data. RESULTS: Activation curve parameters for hNav1.5 in IonWorks HT were not statistically different (p>0.05) from those generated using conventional electrophysiology. IonWorks HT V(1/2)=-22+/-0.8 mV, slope=6.9+/-0.2 (n=11); conventional electrophysiology V(1/2)=-20+/-1.6 mV, slope=6.4+/-0.3 (n=11). Potency values for a range of hNav1.5 blockers determined using IonWorks HT correlated closely with those obtained using conventional electrophysiology (R=0.967, p<0.001). The assay was able to distinguish between highly use-dependent blockers (e.g. tetracaine) and blockers that do not display strong use-dependence (e.g. quinidine). Comparison of the degree of hNav1.5 inhibition and decrease in canine Purkinje fibre action potential upstroke velocity (V(max)) showed that the IonWorks HT assay would have predicted the outcome in Purkinje fibres in the majority of cases, with false negative and positive rates estimated at 8 and 7%, respectively. Finally, hNav1.5 pharmacology was similar when determined using either IonWorks HT or IonWorks Quattro, although the latter yielded more consistent data. DISCUSSION: The assay described combines a functional assessment of hNav1.5 with medium-throughput. Furthermore the assay was able to reveal information on the use-dependency of compound block, as well as predicting Na(+) channel effects in more integrated systems such as the cardiac Purkinje fibre action potential. This makes it possible to determine quantitative potency data, and mechanistic information about use-dependence, in a timeframe short enough to influence medicinal chemistry.

Validity of the modified 20-metre shuttle test: assessment of cardiorespiratory fitness in people who have sustained a traumatic brain injury.

PRIMARY OBJECTIVE: To validate the modified 20-metre shuttle test in adults who have sustained a traumatic brain injury (TBI). DESIGN: Single-sample validity study. SETTING: Brain injury rehabilitation unit. PARTICIPANTS: Twenty-four adults with severe TBI, discharged from hospital for at least 6-months. PROTOCOL: Participants attended the facility for a familiarization session, followed by a symptom-limited treadmill test and a modified shuttle test on two separate days. The treadmill test was based on an individualised protocol which used a physiotherapist-selected speed and increments in gradient every minute until volitional fatigue. The modified shuttle test was externally-paced and commenced with a speed of 2.4 km h(-1) which increased every minute until volitional fatigue. MAIN MEASURES: Four primary measures were taken from both tests: peak oxygen uptake, peak heart rate, maximal velocity and rating of perceived exertion. RESULTS: All participants completed the study. There were no adverse events. A high correlation was observed between the modified shuttle test and the treadmill test for peak oxygen uptake, peak heart rate and maximal velocity (r = 0.96, r = 0.80, r = 0.82, respectively; p < 0.001), but not for rating of perceived exertion (r = 0.013, p = 0.952). CONCLUSION: The modified shuttle test is a valid measure of cardiorespiratory fitness in people who have sustained a TBI.

Local and global calcium signals and fluid and electrolyte secretion in mouse submandibular acinar cells.

Polarized Ca(2+) signals that originate at and spread from the apical pole have been shown to occur in acinar cells from lacrimal, parotid, and pancreatic glands. However, "local" Ca(2+) signals, that are restricted to the apical pole of the cell, have been previously demonstrated only in pancreatic acinar cells in which the primary function of the Ca(2+) signal is to regulate exocytosis. We show that submandibular acinar cells, in which the primary function of the Ca(2+) signal is to drive fluid and electrolyte secretion, are capable of both Ca(2+) waves and local Ca(2+) signals. The generally accepted model for fluid and electrolyte secretion requires simultaneous Ca(2+)-activation of basally located K(+) channels and apically located Cl(-) channels. Whereas a propagated cell-wide Ca(2+) signal is clearly consistent with this model, a local Ca(2+) signal is not, because there is no increase in intracellular Ca(2+) concentration at the basal pole of the cell. Our data provide the first direct demonstration, in submandibular acinar cells, of the apical and basal location of the Cl(-) and K(+) channels, respectively, and confirm that local Ca(2+) signals do not Ca(2+)-activate K(+) channels. We reevaluate the model for fluid and electrolyte secretion and demonstrate that Ca(2+)-activation of the Cl(-) channels is sufficient to voltage-activate the K(+) channels and thus demonstrate that local Ca(2+) signals are sufficient to support fluid secretion.

Effect of 10-day cast immobilization on sarcoplasmic reticulum calcium regulation in humans.

This study investigated the effects of 10-day lower limb cast immobilization on sarcoplasmic reticulum (SR) Ca2+ regulation. Muscle biopsies were analysed in eight healthy females for maximal rates of SR Ca2+ release, Ca2+ uptake and Ca2+ ATPase activity at control, during immobilization at day 3 (IM 3), day 6 (IM 6) and day 10 (IM 10). Quadriceps muscle cross-sectional area (CSA) and 1-repetition maximum (1RM) leg extension strength were measured to determine the extent of muscle size and strength adaptations. Muscle CSA and strength decreased following 10 days of immobilization (11.8 and 41.6%, respectively, P < 0.01). A decrease in SR Ca2+ uptake rate (analysed per g wet wt) was found at IM 3 (13.2%, P=0.05), with a further decrease at IM 10 (19.8% from control, P < 0.01). At IM 10, a decrease in SR Ca2+ uptake rate (per mg protein) also occurred (19.9%, P < 0.01). Sarcoplasmic reticulum Ca2+ ATPase activity and rate of Ca2+ release were not altered with 10 days of immobilization. This study observed a decrease in SR Ca2+ uptake rate, muscular atrophy and strength loss over 10 days of immobilization in humans.

Acetylcholine-evoked calcium mobilization and ion channel activation in human labial gland acinar cells from patients with primary Sjögren's syndrome.

Recent evidence has indicated that the salivary gland dysfunction associated with Sjögren's syndrome (SjS) is not necessarily due to immune-mediated destruction of acinar tissue. SjS sufferers may possess substantial reserves of acinar tissue but nevertheless be incapable of maintaining salivary flow rates in the normal range. We have investigated the ability of isolated labial gland acinar cells from SjS patients to fluid secrete by measuring agonist-evoked changes in intracellular Ca(2+) ([Ca(2+)](i)) using fura-2 microfluorimetry and activation of K(+) and Cl(-) channels using the patch-clamp whole cell technique. We can confirm that stimulation with a super-maximal dose of acetylcholine (ACh) increased [Ca(2+)]i equally in both control acinar cells and those derived from SjS patients. However, at submaximal concentrations, the dose-response curve for ACh was shifted to the right by approximately one order of magnitude in acinar cells from SjS patients compared to control acinar cells. Patch-clamp measurements consistent with the presence of Ca(2+)-activated K(+) and Cl(-) conductances were obtained from both control acinar cells and those obtained from SjS patients. Dose-dependent activation of the ion channels by acetylcholine was also right-shifted in acinar cells from SjS patients compared to control cells. Our data show that labial gland acinar cells from SjS patients were capable of responding to agonist stimulation by mobilizing [Ca(2+)](i) and activating K(+) and Cl(-) channels consistent with the requirements of fluid secretion. However, the persistent loss of sensitivity to ACh observed in from SjS patients may account for the lack of saliva production observed in these patients in vivo.

Role of Ins(1,4,5)P3, cADP-ribose and nicotinic acid-adenine dinucleotide phosphate in Ca2+ signalling in mouse submandibular acinar cells.

cADP-ribose (cADPr) and nicotinic acid-adenine dinucleotide phosphate (NAADP) are two putative second messengers; they were first shown to stimulate Ca(2+) mobilization in sea urchin eggs. We have used the patch-clamp whole-cell technique to determine the role of cADPr and NAADP in relation to that of Ins(1,4,5)P(3) in mouse submandibular acinar cells by measuring agonist-evoked and second-messenger-evoked changes in Ca(2+)-dependent K(+) and Cl(-) currents. Both Ins(1,4,5)P(3) and cADPr were capable of reproducing the full range of responses normally seen in response to stimulation with acetylcholine (ACh). Low concentrations of agonist (10-20 nM ACh) or second messenger [1-10 microM Ins(1,4,5)P(3) or cADPr] elicited a sporadic transient activation of the Ca(2+)-dependent currents; mid-range concentrations [50-500 nM ACh, 50 microM Ins(1,4,5)P(3) or 50-100 microM cADPr] elicited high-frequency (approx. 2 Hz) trains of current spikes; and high concentrations [more than 500 nM ACh, more than 50 microM Ins(1,4,5)P(3) or more than 100 microM cADPr] gave rise to a sustained current response. The response to ACh was inhibited by antagonists of both the Ins(1,4,5)P(3) receptor [Ins(1,4,5)P(3)R] and the ryanodine receptor (RyR) but could be completely blocked only by an Ins(1,4,5)P(3)R antagonist (heparin). NAADP (50 nM to 100 microM) did not itself activate the Ca(2+)-dependent ion currents, nor did it inhibit the activation of these currents by ACh. These results show that, in these cells, both Ins(1,4,5)P(3)R and RyR are involved in the propagation of the Ca(2+) signal stimulated by ACh and that cADPr can function as an endogenous regulator of RyR. Furthermore, although NAADP might have a role in hormone-stimulated secretion in pancreatic acinar cells, it does not contribute to ACh-evoked secretion in submandibular acinar cells.

Skeletal muscle metabolic and ionic adaptations during intense exercise following sprint training in humans.

The effects of sprint training on muscle metabolism and ion regulation during intense exercise remain controversial. We employed a rigorous methodological approach, contrasting these responses during exercise to exhaustion and during identical work before and after training. Seven untrained men undertook 7 wk of sprint training. Subjects cycled to exhaustion at 130% pretraining peak oxygen uptake before (PreExh) and after training (PostExh), as well as performing another posttraining test identical to PreExh (PostMatch). Biopsies were taken at rest and immediately postexercise. After training in PostMatch, muscle and plasma lactate (Lac(-)) and H(+) concentrations, anaerobic ATP production rate, glycogen and ATP degradation, IMP accumulation, and peak plasma K(+) and norepinephrine concentrations were reduced (P<0.05). In PostExh, time to exhaustion was 21% greater than PreExh (P<0.001); however, muscle Lac(-) accumulation was unchanged; muscle H(+) concentration, ATP degradation, IMP accumulation, and anaerobic ATP production rate were reduced; and plasma Lac(-), norepinephrine, and H(+) concentrations were higher (P<0.05). Sprint training resulted in reduced anaerobic ATP generation during intense exercise, suggesting that aerobic metabolism was enhanced, which may allow increased time to fatigue.

The effect of inositol 1,3,4,5-tetrakisphosphate on inositol trisphosphate-induced Ca2+ mobilization in freshly isolated and cultured mouse lacrimal acinar cells.

Earlier reports have shown a remarkable synergism between InsP(4) and InsP(3) [either Ins(1,4,5)P(3) or Ins(2,4,5)P(3)] in activating Ca(2+)-dependent K(+) and Cl(-) currents in mouse lacrimal cells [Changya, Gallacher, Irvine, Potter and Petersen (1989) J. Membr. Biol. 109, 85-93; Smith (1992) Biochem. J. 283, 27-30]. However, Bird, Rossier, Hughes, Shears, Armstrong and Putney [(1991) Nature (London) 352, 162-165] reported that they could see no such synergism in the same cell type. A major experimental difference between the two laboratories lies in whether or not the cells were maintained in primary culture before use. Here we have compared directly the responses to inositol polyphosphates in freshly isolated cells versus cells cultured for 6-72 h. In the cultured cells, Ins(2,4,5)P(3) at 100 microM produced a robust stimulation of K(+) and Cl(-) currents, as much as an order of magnitude greater than that observed in the freshly isolated cells. However, the freshly isolated cells could be restored to a sensitivity similar to cultured cells by the addition of InsP(4) at a concentration two orders of magnitude lower than that of Ins(2,4,5)P(3). We discuss the implications of this with respect to the actions of InsP(4), including the possibility that disruption of the cellular structure during the isolation of the cells exposes an extreme manifestation of a possible physiological role for InsP(4) in controlling calcium-store integrity.

Human skeletal sarcoplasmic reticulum Ca2+ uptake and muscle function with aging and strength training.

This study investigated the adaptations of skeletal muscle sarcoplasmic reticulum (SR) Ca2+ uptake, relaxation, and fiber types in young (YW) and elderly women (EW) to high-resistance training. Seventeen YW (18-32 yr) and 11 EW (64-79 yr) were assessed for 1) electrically evoked relaxation time and rate of the quadriceps femoris; and 2) maximal rates of SR Ca2+ uptake and Ca2+-ATPase activity and relative fiber-type areas, analyzed from muscle biopsies of the vastus lateralis. EW had significantly slower relaxation rates and times, decreased SR Ca2+ uptake and Ca2+-ATPase activity, and a larger relative type I fiber area than did YW. A subgroup of 9 young (YWT) and 10 elderly women (EWT) performed 12 wk of high-resistance training (8 repetition maximum) of the quadriceps and underwent identical testing procedures pre- and posttraining. EWT significantly increased their SR Ca2+ uptake and Ca2+-ATPase activity in response to training but showed no alterations in speed of relaxation or relative fiber-type areas. In YWT none of the variables was altered after resistance training. These findings suggest that 1) a reduced SR Ca2+ uptake in skeletal muscle of elderly women was partially reversed with resistance training and 2) SR Ca2+ uptake in the vastus lateralis was not the rate-limiting mechanism for the slowing of relaxation measured from electrically evoked quadriceps muscle of elderly women.

Impaired calcium pump function does not slow relaxation in human skeletal muscle after prolonged exercise.

This study examined the effects of prolonged exercise on human quadriceps muscle contractile function and homogenate sarcoplasmic reticulum Ca2+ uptake and Ca2+-adenosinetriphosphatase activity. Ten untrained men cycled at 75 +/- 2% (SE) peak oxygen consumption until exhaustion. Biopsies were taken from the right vastus lateralis muscle at rest, exhaustion, and 20 and 60 min postexercise. Peak tension and half relaxation time of the left quadriceps muscle were measured during electrically evoked twitch and tetanic contractions and a maximal voluntary isometric contraction at rest, exhaustion, and 10, 20, and 60 min postexercise. At exhaustion, homogenate Ca2+ uptake and Ca2+ adenosinetriphosphatase activity were reduced by 17 +/- 4 and 21 +/- 5%, respectively, and remained depressed after 60 min recovery (P

Effects of training on potassium, calcium and hydrogen ion regulation in skeletal muscle and blood during exercise.

Ionic regulation is critical to muscle excitation, contraction and metabolism, and thus for muscle function during exercise. This review focuses on the effects of training upon K+, Ca2+ and H+ ion regulation in muscle and K+ regulation in blood during exercise. Training enhances K+ regulation in muscle and blood and reduces muscular fatiguability. Endurance, sprint and strength training in humans induce an increased muscle Na+, K+ pump concentration, usually associated with a reduced rise in plasma [K+] during exercise. Although impaired muscle Ca2+ regulation plays a vital role in fatigue, little is known about possible training effects. In rat fast-twitch muscle, overload-induced hypertrophy and endurance training were associated with reduced sarcoplasmic reticulum Ca2+ uptake, consistent with fast-to-slow fibre transition. In human muscle, endurance and strength training had no effect on muscle Ca2+ ATPase concentration. Whilst muscle Ca2+ uptake, release and Ca2+ ATPase activity were depressed by fatigue, no differences were found between strength athletes and untrained individuals. Muscle H+ accumulation may contribute to fatigue during intense exercise and is also modified by sprint training. Sprint training may increase muscle Lac- and work output with exhaustive exercise, but the rise in muscle [H+] is unchanged or attenuated, indicating a reduced rise in muscle [H+] relative to work performed. Muscle buffering capacity can be dissociated from this improved H+ regulatory capacity after training. Thus, training enhances muscle and blood K+ and muscle H+ regulation during exercise, consistent with improved muscular performance and reduced fatiguability; however, little is known about training effects on muscle Ca2+ regulation during contraction.