Contractile properties of in situ perfused skeletal muscles from rats with congestive heart failure

We hypothesized that in congestive heart failure (CHF) slow-twitch but not fast-twitch muscles exhibit decreased fatigue resistance in the sense of accelerated reduction of muscle force during activity. Experiments were carried out on anaesthetized rats 6 weeks after induction of myocardial infarction or a sham operation (Sham). Animals with left ventricular end-diastolic pressure (LVEDP) > 15 mmHg under anaesthesia were selected for the CHF group. There was no muscle atrophy in CHF. Force generation by in situ perfused soleus (Sol) or extensor digitorum longus (EDL) muscles was recorded during stimulation (trains at 5 Hz for 6 s (Sol) or 10 Hz for 1.5 s (EDL) at 10 or 2.5 s intervals, respectively) for 1 h in Sol and 10 min in EDL at 37 °C. Initial force was almost the same in Sol from CHF and Sham rats, but relaxation was slower in CHF. Relaxation times (95–5 % of peak force) were 177 ± 55 and 131 ± 44 ms in CHF and Sham, respectively, following the first stimulation train. After 2 min of stimulation the muscles transiently became slower and maximum relaxation times were 264 ± 71 and 220 ± 45 ms in CHF and Sham, respectively (   P < 0.05  ). After 60 min they recovered to 204 ± 60 and 122 ± 55 ms in CHF and Sham, respectively (   P < 0.05  ). In CHF but not in Sham rats the force of contraction of Sol declined from the second to the sixtieth minute to 70 % of peak force. The EDL of both CHF and Sham fatigued to 24–28 % of initial force, but no differences in contractility pattern were detected. Thus, slow-twitch muscle is severely affected in CHF by slower than normal relaxation and significantly reduced fatigue resistance, which may explain the sensation of both muscle stiffness and fatigue in CHF patients.     

Assessment of aldehyde dehydrogenase in viable cells

Cytosolic aldehyde dehydrogenase (ALDH), an enzyme responsible for oxidizing intracellular aldehydes, has an important role in ethanol, vitamin A, and cyclophosphamide metabolism. High expression of this enzyme in primitive stem cells from multiple tissues, including bone marrow and intestine, appears to be an important mechanism by which these cells are resistant to cyclophosphamide. However, although hematopoietic stem cells (HSC) express high levels of cytosolic ALDH, isolating viable HSC by their ALDH expression has not been possible because ALDH is an intracellular protein. We found that a fluorescent aldehyde, dansyl aminoacetaldehyde (DAAA), could be used in flow cytometry experiments to isolate viable mouse and human cells based on their ALDH content. The level of dansyl fluorescence exhibited by cells after incubation with DAAA paralleled cytosolic ALDH levels determined by Western blotting and the sensitivity of the cells to cyclophosphamide. Moreover, DAAA appeared to be a more sensitive means of assessing cytosolic ALDH levels than Western blotting. Bone marrow progenitors treated with DAAA proliferated normally. Furthermore, marrow cells expressing high levels of dansyl fluorescence after incubation with DAAA were enriched for hematopoietic progenitors. The ability to isolate viable cells that express high levels of cytosolic ALDH could be an important component of methodology for identifying and purifying HSC and for studying cyclophosphamide-resistant tumor cell populations.     

Extreme sarcoplasmic reticulum volume loss and compensatory T-tubule remodeling after Serca2 knockout

Cardiomyocyte contraction and relaxation are controlled by Ca(2+) handling, which can be regulated to meet demand. Indeed, major reduction in sarcoplasmic reticulum (SR) function in mice with Serca2 knockout (KO) is compensated by enhanced plasmalemmal Ca(2+) fluxes. Here we investigate whether altered Ca(2+) fluxes are facilitated by reorganization of cardiomyocyte ultrastructure. Hearts were fixed for electron microscopy and enzymatically dissociated for confocal microscopy and electrophysiology. SR relative surface area and volume densities were reduced by 63% and 76%, indicating marked loss and collapse of the free SR in KO. Although overall cardiomyocyte dimensions were unaltered, total surface area was increased. This resulted from increased T-tubule density, as revealed by confocal images. Fourier analysis indicated a maintained organization of transverse T-tubules but an increased presence of longitudinal T-tubules. This demonstrates a remarkable plasticity of the tubular system in the adult myocardium. Immunocytochemical data showed that the newly grown longitudinal T-tubules contained Na(+)/Ca(2+)-exchanger proximal to ryanodine receptors in the SR but did not contain Ca(2+)-channels. Ca(2+) measurements demonstrated a switch from SR-driven to Ca(2+) influx-driven Ca(2+) transients in KO. Still, SR Ca(2+) release constituted 20% of the Ca(2+) transient in KO. Mathematical modeling suggested that Ca(2+) influx via Na(+)/Ca(2+)-exchange in longitudinal T-tubules triggers release from apposing ryanodine receptors in KO, partially compensating for reduced SERCA by allowing for local Ca(2+) release near the myofilaments. T-tubule proliferation occurs without loss of the original ordered transverse orientation and thus constitutes the basis for compensation of the declining SR function without structural disarrangement.     

Synergistic effect of aqueous extract of Telfaria occidentalis on the biological activities of artesunate in Plasmodium berghei infected mice

Background

Resistance to most antimalarial drugs has encouraged the use of herbal preparations along with prescribed orthodox drugs.

Objective

To investigate effect of co-administration of aqueous extract of T. occidentalis leaves; commonly used as antimalarial and haematinic agent in Nigeria and artesunate using P. berghei animal model.

Methods

In vivo curative antiplasmodial effect of T. occidentalis (200mg/kg) alone and combination with artesunate (2mg/kg) were evaluated using albino mice infected with 10⁶ parasitized erythrocytes of P. berghei intraperitoneally. The haematological parameters: haemoglobin level, red blood cells and white blood cells and packed cell volume were monitored using standard methods.

Results

Aqueous extract of T. occidentalis, artesunate and the combination gave 72.17±4.07%, 70.43± 4.27% and 85.43±3.65% reduction in parasitaemia after 48hours respectively. A significant enhancement of the PCV was obtained with the coadministration of artesunate and aqueous extract (p< 0.01). Similar trends were also observed with heamatological parameters at 72hours of administration.

Conclusion

This study revealed a synergistic effect of the co-administration on parasite clearance rate of P. berghei infection in mice, with a significant enhancement of haematological parameters within 48 hours of administration. This indicates a rapid rate of recovery from plasmodial infections with the co-administration.     

Intrinsic skeletal muscle alterations in chronic heart failure patients: a disease-specific myopathy or a result of deconditioning?

Chronic heart failure (CHF) patients frequently experience impaired exercise tolerance due to skeletal muscle fatigue. Studies suggest that this in part is due to intrinsic alterations in skeletal muscle of CHF patients, often interpreted as a disease-specific myopathy. Knowledge about the mechanisms underlying these skeletal muscle alterations is of importance for the pathophysiological understanding of CHF, therapeutic approach and rehabilitation strategies. We here critically review the evidence for skeletal muscle alterations in CHF, the underlying mechanisms of such alterations and how skeletal muscle responds to training in this patient group. Skeletal muscle characteristics in CHF patients are very similar to what is reported in response to chronic obstructive pulmonary disease (COPD), detraining and deconditioning. Furthermore, skeletal muscle alterations observed in CHF patients are reversible by training, and skeletal muscle of CHF patients seems to be at least as trainable as that of matched controls. We argue that deconditioning is a major contributor to the skeletal muscle dysfunction in CHF patients and that further research is needed to determine whether, and to what extent, the intrinsic skeletal muscle alterations in CHF represent an integral part of the pathophysiology in this disease.     

EC-coupling in normal and failing hearts

Systolic heart failure may be due to too few cardiomyocytes, or to reduced contractile function of the heart cells. In the latter situation the myocardial function is impaired and this condition is called myocardial failure. The pathophysiological mechanism behind this cellular defect is not known, but Ca2+ handling is altered. Although the most important trigger of sarcoplasmatic reticulum (SR) Ca2+ release, the L-type Ca2+ current, seems to be unaltered, SR Ca2+ load is reduced in human heart failure. This could explain the reduced contractility observed in failing hearts. Three possible mechanisms have been suggested to explain the reduction in SR Ca2+ load. They are leak through the SR Ca2+ release channel (RyR), impaired SR Ca2+ ATPase (SERCA) function and increased Na+/Ca2+-exchanger (NCX) function. Leak through RyR is not consistently found. Increased NCX function is probably secondary to a change in Ca2+ handling, and thus not a primary mechanism, but blockade of the NCX might have therapeutic potential. Reduced SERCA function is probably a primary mechanism for the observed systolic dysfunction, and further insight is to be gained through studies in genetically modified models.     

Loss of potassium from muscle during moderate exercise in humans: a result of insufficient activation of the Na+-K+-pump?

In this study, we have investigated whether the muscle net potassium (K+) loss, observed during two-legged intermittent static knee-extensions at 30% MVC (n = 9), is caused by an insufficient activation of the Na+-K+-pumps. Furthermore, we have investigated whether the changes in the K+ homeostasis can be causally related to fatigue. K+ loss was calculated from the arterio-venous concentration difference and plasma flow. In three subjects, femoral venous K+ concentration was measured continuously with a K+ selective electrode. Na+-K+-pump activity was estimated from the rate of removal of K+ from the blood during 30-s pauses inserted into the exercise protocol. A large net K+ loss took place during the first minutes of exercise, but diminished quickly and disappeared after 20 min. An increasing net K+ loss reappeared after 30 min. Only 10% of the lost K+ had been regained after the 20-min recovery. A lag in the activation of the Na+-K+-pumps may explain the K+ loss at the beginning of exercise, but gradual pump activation prevented a net K+ loss after 20 min of exercise. The reappearance of the net K+ loss in the later stage of exercise and the subsequent slow recovery of intracellular K+ seemed to be caused by an insufficient further activation of the pumps, rather than by the capacity of the pumps being surpassed. Fatigue was not related to the accumulation of K+ in the interstitium. However, during exercise, the decrease in intracellular K+ content was linearly related to the fall of maximal force. We conclude that during repeated isometric contractions, insufficient activation of the Na+-K+-pumps causes a continuous muscle K+ loss which was associated with fatigue.     

In-vivo quantification of myocardial Na-K pump rate during beta-adrenergic stimulation of intact pig hearts

Maintenance of adequate electrical activity of the heart depends critically on the ability of the Na-K pump to compensate for normal passive sodium and potassium fluxes. Using sudden injections of [3H]ouabain into the left coronary artery in anaesthetized open-chest pigs, we monitored transient changes in myocardial potassium balance by PVC-valinomycin mini-electrodes. When related to the number of pumps blocked and fractional inhibition, these data provided estimates of total Na-K pump capacity as well as actual pump rate and perturbations of the Na-K balance. Experiments were performed in hearts with and without intracoronary isoprenaline infusion (2.5 nmol min-1). After injection of 120 nmol [3H]ouabain into the left coronary artery, myocardial [3H]ouabain concentrations were 118 (74-178) and 103 (76-145) pmol g-1 and total concentrations of [3H]ouabain binding sites were 893 (752-1076) and 785 (691-877) pmol g-1 (median, 95% confidence interval) in isoprenaline-treated and control hearts respectively (differences not significant). The [3H]ouabain injection caused a net potassium release of 81 (56-132) and 43 (23-75) mumol 100 g-1 (median, 95% confidence interval) in isoprenaline-treated and control hearts respectively (n = 6-8; significance of difference, P = 0.03). Na-K pump rate estimated from mono-exponential release curves was 6363 (3942-10,858) K+ ions min-1 site-1 during beta-adrenoceptor stimulation and 2514 (1380-4322) in control (significance of difference, P = 0.03). This corresponds to 40 and 16%, respectively, of the maximum possible pump rate determined from ATP hydrolysis. Comparison of accumulated potassium release and relative Na-K pump rate indicates that catecholamines enhance the sensitivity of the Na-K pump for intracellular sodium.