Sodium nitroprusside,a NO donor,modifies Ca2+ transport and mechanical properties in frog skeletal muscle

Recently it has been hypothesized that, in skeletal muscle, NO produced directly by high-frequency stimulation could produce contraction through reactions with thiol groups on the sarcoplasmic reticulum (SR). However, a possible cGMP-mediated relaxing effect, similar to that seen in smooth muscle, has also been demonstrated. We used purified SR preparations and single fibres from frog fast muscles incubated with different concentrations of sodium nitroprusside (SNP) in this study. The results obtained from a long low-frequency stimulation, together with those from a study on Ca2+ transport regulation, showed that the presence of NO precursor induced: an acceleration of the onset of fatigue in single fibres; a decreased vesicular Ca2+ content due to increased Ca2+ release; a shift to open status in SR Ca2+ channels; an increase in SR Ca2+ pump activity. The data presented in this paper seem to indicate that the increased NO in the muscle fibres can influence muscle activity in different ways, perhaps depending on the metabolic status of the muscle and target (filaments, sarcolemma, SR) with which the NO (or its derivatives) acts.     

Age and sex influence on oxidative damage and functional status in human skeletal muscle

A reduction in muscle mass, with consequent decrease in strength and resistance, is commonly observed with advancing age. In this study we measured markers of oxidative damage to DNA, lipids and proteins, some antioxidant enzyme activities as well Ca²⁺ transport in sarcoplasmic reticulum membranes in muscle biopsies from vastus lateralis of young and elderly healthy subjects of both sexes in order to evaluate the presence of age- and sex- related differences. We found a significant increase in oxidation of DNA and lipids in the elderly group, more evident in males, and a reduction in catalase and glutathione transferase activities. The experiments on Ca²⁺ transport showed an abnormal functional response of aged muscle after exposure to caffeine, which increases the opening of Ca²⁺ channels, as well a reduced activity of the Ca²⁺ pump in elderly males. From these results we conclude that oxidative stress play an important role in muscle aging and that oxidative damage is much more evident in elderly males, suggesting a gender difference maybe related to hormonal factors.This revised version was published online in September 2005 with corrections to the Cover Date.     

Effect of paradoxical sleep deprivation on dna synthesis in fetal rat brain

We have investigated the effect of PS-D induced in gestating rats by treatment with clomipramine or with the platform technique on the process of DNA synthesis taking place in fetal organs. This parameter was taken as a biochemical index of ongoing cellular proliferation. In brain and, to a minor extent, in liver and kidney the rate of fetal DNA synthesis was markedly increased in both experimental groups. The effect was more prominent in the clomipramine group. PS-D treatment of gestating rats, notably by the platform technique, left long-lasting effects in the offspring with regard to organ weight and DNA concentration as well as to learning capacity. It is concluded that the occurrence of PS in gestating rats may exert a significant influence on fetal development.     

Circadian oscillations of DNA synthesis in rat brain

The possibility that the synthesis of brain DNA undergoes a circadian fluctuation was examined in male adult Wistar rats, kept under natural lighting conditions or born and raised under artificial lighting conditions. Groups of rats were taken every 4 h during the 24 h, injected subcutaneously with [methyl-3H]thymidine and killed 4 h later. By cosinor analysis, the DNA specific activity of cerebral hemispheres and brainstem was found to show a significant 24 h rhythm with the peak at the beginning of the dark period (waking period). By contrast, in kidney, the peak of the circadian rhythm of DNA specific activity occurred during the light period (sleep period), in agreement with literature data. On the other hand, in 4-week-old rats, born and raised in artificial lighting conditions, brain DNA specific activity followed a 12 h rhythm, in agreement with the lack of a significant diurnal oscillation of the sleep--waking structure. It is concluded that brain DNA synthesis undergoes a circadian fluctuation in association with the circadian rhythm of waking.     

Psychometric testing of the Immigrant Barriers to Health Care Scale: Hispanic Version

Barriers to care contribute to health inequities for immigrant populations. Although inadequate health insurance is a known barrier, other factors impact the issue. Few instruments exist to specifically measure these other barriers. The purpose of this study was to test the Immigrant Barriers to Health Care Scale – Hispanic Version. It was first pilot-tested in southern California with a Mexican population. After refinement, the instrument was tested in a north-eastern sample of diverse Hispanic adults. The data were analyzed using exploratory factor analysis. Factor loadings and communalities were used to assess the adequacy of the scale's items. Six items were deleted due to ambiguous factor loadings. The final 11 items loaded onto four factors and explained 54.58% of the variance. The coefficient alpha was 0.81 for the instrument. The Immigrant Barriers to Health Care Scale is a reliable and valid tool. Its further use and reporting with other socially and economically disadvantaged groups is advised.     

Functional aspects of calcium transport in sarcoplasmic reticulum vesicles derived from frog skeletal muscle treated with saponin

Summary To study the physiological aspects of the excitation-contraction cycle, saponin (10–100g ml^–1) was used as a skinning agent on muscle and sarcotubular vesicles derived from fast muscles (sartorius and tibialis anterior) ofRana esculenta.The vesicles showed similar Ca²⁺-ATPase activity and similar protein profiles carried out by SDS-PAGE. Calcium transport in untreated vesicles and those treated with different concentrations of saponin seemed to have the same quantitative and qualitative parameters if the saponin was used in a range between 10 and 50g ml^–1.Our results confirm that saponin may be considered to be a valid skinning agent for the external membranes of fast skeletal muscles.     

Modifications of Ca2+ transport induced by glutathione in sarcoplasmic reticulum membranes of frog skeletal muscle

The Ca²⁺ transport across the membrane of vesicles purified from the sarcoplasmic reticulum (SR) of frog skeletal muscle is modified by raising the concentration of the reduced form of glutathione (GSH). Passive release of Ca²⁺ is inhibited through the direct action of GSH on ryanodine receptors while active uptake is increased by a dose-dependent stimulation of Ca²⁺ pumps (Ca²⁺-ATPase). These effects are physiological since the concentrations of GSH utilised (0.01–10.0 mM) are compatible with the in vivo concentration of this antioxidant. They are independent of the external Ca²⁺ concentration and are specific for the reduced form of glutathione, since the disulphide form (GSSG) or other GSH-derivatives do not induce these effects.     

Evaluation of indices of skeletal muscle contraction in areas of referred hyperalgesia from an artificial ureteric stone in rats

We investigated the incidence and the number of microbleeds (MBs) on T2*-weighted gradient-echo magnetic resonance imaging in 30 Binswanger's disease (BD) patients with diffuse white matter lesions and a varying degree of lacunar infarction, 51 multiple lacunar stroke (MLS) patients with multiple lacunar infarction and no or mild white matter lesions, and 59 elderly controls. MBs were found in 23 (77%) patients with BD, 26 (51%) patients with MLS, and 5 (8%) controls, and the incidence and the number of MBs were significantly greater in the BD group compared with MLS and control groups. Patients with BD had a more widespread location of MBs. More specifically, MBs were commonly found in areas within or surrounded by white matter lesions of the patients with BD. When 81 patients from both the BD and MLS groups were analyzed, logistic regression analysis showed that number of lacunar infarct, severity of white matter hyperintensity, and use of antiplatelet agents were significantly associated with MBs. Patients with BD exhibited a high frequency and number of MBs, indicating advanced bleeding-prone microangiopathy within the brain, which should be taken into account in treatment and management.