Role of intracellular pH in muscle fatigue

Intracellular pH of in vitro diaphragm preparations was determined following low- (5 Hz, 1.5 min) and high- (75 Hz, 1 min) frequency stimulation, using glass microelectrodes of the liquid membrane type (pHm). Results were compared with values obtained by the standard homogenate technique (pHh). High- and low-frequency stimulation reduced peak tetanic tension to 21 +/- 1 (SE) and 71 +/- 2% of initial values, respectively. Peak tetanic tension returned to resting values after 10- to 15-min recovery from high- or low-frequency stimulation. Resting pHm was 7.063 +/- 0.011 (n = 72), and after fatiguing stimulation declined to values as low as 6.33. During recovery pHm significantly increased and by 10 min had returned to prefatigue values. No difference was observed in the recovery of pHm between the low- and high-frequency stimulation groups (analysis of variance test, ANOVA), and in both groups pHm recovery was highly correlated to the recovery of peak tetanic tension (r = 0.94, P less than 0.001). Resting pHh was 7.219 +/- 0.023 (n = 13), which was significantly higher than the pHm value. In contrast to pHm, intracellular pHh was significantly higher during recovery from 75- vs. 5-Hz stimulation (P less than 0.05). For both groups pHh increased significantly with time and by 10 min returned to prestimulation values. The ANOVA test demonstrated that pHh values were significantly higher than pHm values during recovery from fatigue. The results from this study support our hypothesis that fatigue from both high- and low-frequency stimulation is at least partially due to the deleterious effects of intracellular acidosis on excitation-contraction coupling.     

Ischemia-reperfusion injury: biochemical alterations in peroxisomes of rat kidney.

Exogenously supplied catalase, a peroxisomal enzyme, has been found to be of therapeutic value in ischemic injury. Therefore, we examined the effect of ischemic-reperfusion injury on the structure and function of kidney peroxisomes. Ischemic injury changed the density of peroxisomes from 1.21 g/cm3 (peak I) to a lighter density of 1.14 g/cm3 (peak II). The number of peroxisomes moving from the normal density population (peak I) to a lower density population (peak II) increased with an increase in ischemic injury. Latency experiments indicated both populations of peroxisomes to be of intact peroxisomes. Immunoblot analysis with antibodies against peroxisomal matrix and membrane proteins demonstrated that after 90 min of ischemia a significant number of matrix proteins were lost in the peak II population, suggesting that functions of these peroxisomes may be severally affected. Reperfusion following ischemic injury resulted in loss of peroxisomal matrix proteins in both peaks I and II, suggesting that peroxisomal functions may be drastically compromised. This change in peroxisomal functions is reflected by a significant decrease in peroxisomal catalase activity (35%) and beta-oxidation of lignoceric acid (43%) observed following 90 min of ischemia. The decrease in catalase activity was more pronounced in reperfused kidneys even after a shorter term of ischemic injury. Reperfusion restored the normal peroxisomal beta-oxidation in kidneys exposed up to 60 min of ischemia. However, 90 min of ischemia was irreversible as there was a further decrease in beta-oxidation upon reperfusion. The decrease in catalase activity during ischemia alone was due to the formation of an inactive complex, whereas during reperfusion, following 90 min of ischemia, inactivation and proteolysis or decreased synthesis of catalase contributed equally toward the injury. The observed changes in the structure and function of peroxisomes as a result of ischemic-reperfusion injury and the ubiquitous distribution of peroxisomes underlines the importance of this organelle in the pathophysiology of vascular injury in general.     

Behavioral stereotypy in old and young rhesus monkeys

Four old (25 years) and six young (3 years) female rhesus monkeys (Macaca mulatta) were observed individually in a laboratory cage with either an old or a young monkey present as a social partner. The behavioral repertoire was coded into ten mutually exclusive and exhaustive categories. An information analysis of the individual behavior records is presented along with subject and partner age effects on the frequency of bouts and the amount of time spent in each category of behavior. Knowledge of the relative frequencies of the behaviors tells more about the behavior of young than old monkeys; and knowledge of the preceding behavior tells more about the behavior of old than young monkeys. Further, knowledge of the relative frequencies tells more about the behavior of both old and young monkeys with junior or elder partners than with age peers; whereas knowledge of the preceding behavior is more informative for old monkeys than for young ones regardless of the partner's age. Both old and young engaged in more affiliative behaviors with age peers than with junior or elder partners. An hypothesis is proposed which relates this social homophyly to the age difference in behavioral stereotypy.     

DNA-DNA hybridization assay for detection of Salmonella spp. in foods

We have developed a DNA-DNA hybridization test for the presence of Salmonella spp. in foods. This test requires an initial pre-enrichment of food samples in nutrient broth but does not require selective enrichment. Samples of food cultures are collected on membrane filters and assayed by molecular hybridization to labeled probes. The probes consist of DNA sequences which are unique to the genus Salmonella and are widely distributed in the genus. A diverse panel of foods was assayed successfully by this methodology.     

Effects of thyrotoxicosis on mitochondrial enzymes of rat soleus.

Cytochrome oxidase, glycerol-3-phosphate dehydrogenase, and succinate dehydrogenase were measured in mitochondrial fractions obtained from rat soleus muscle of control and 8 week T3 + T4 treated animals. Under these conditions of prolonged treatment, there is a five-fold increase in the specific activities of both cytochrome oxidase and glycerole-3-phosphate dehydrogenase. Significant increases in total cellular mitochondrial content and enzyme activities were observed in T3 + T4 treated animals as compared to controls. These results indicate that thyrotoxicosis can induce selective changes in mitochondrial enzymes in slow twitch red (Type I) muscle fibers.     

Optimization and Technological Development Strategies of an Antimicrobial Extract from Achyrocline alata Assisted by Statistical Design

Achyrocline alata, known as Jateí-ka-há, is traditionally used to treat several health problems, including inflammations and infections. This study aimed to optimize an active extract against Streptococcus mutans, the main bacteria that causes caries. The extract was developed using an accelerated solvent extraction and chemometric calculations. Factorial design and response surface methodologies were used to determine the most important variables, such as active compound selectivity. The standardized extraction recovered 99% of the four main compounds, gnaphaliin, helipyrone, obtusifolin and lepidissipyrone, which represent 44% of the extract. The optimized extract of A. alata has a MIC of 62.5 μg/mL against S. mutans and could be used in mouth care products.     

Interactions among oscillatory pathways in NF-kappa B signaling

Background  

Sustained stimulation with tumour necrosis factor alpha (TNF-alpha) induces substantial oscillations—observed at both the single cell and population levels—in the nuclear factor kappa B (NF-kappa B) system. Although the mechanism has not yet been elucidated fully, a core system has been identified consisting of a negative feedback loop involving NF-kappa B (RelA:p50 hetero-dimer) and its inhibitor I-kappa B-alpha. Many authors have suggested that this core oscillator should couple to other oscillatory pathways.     

Subfornical organ disconnection alters Fos expression in the lamina terminalis, supraoptic nucleus, and area postrema after intragastric hypertonic NaCl

The lamina terminalis was severed by a horizontal knife cut through the anterior commissure to determine the effects of a disconnection of the subfornical organ (SFO) on drinking and Fos-like immunoreactivity (Fos-ir) in the rat brain in response to an intragastric load of hypertonic saline (5 ml/kg of 1.5 M NaCl by gavage). After an initial load, knife-cut rats drank significantly less water than sham-cut rats, thus confirming a role for the SFO in osmotic drinking. After a second load at least 1 wk later, the rats were not allowed to drink after the gavage and were perfused for analysis of Fos-ir at 90 min. Compared with sham-cut rats, the knife-cut rats displayed significantly elevated Fos-ir in the main body of the SFO, in the dorsal cap of the organum vasculosum laminae terminalis, and in the ventral median preoptic nucleus after the hypertonic load. The knife cut significantly decreased Fos-ir in the supraoptic nucleus. Fos-ir was expressed mainly in the midcoronal and caudal parts of the area postrema of sham-cut rats, and this expression was greatly reduced in knife-cut rats. These findings strengthen the case for the presence of independently functioning osmoreceptors within the SFO and suggest that the structures of the lamina terminalis provide mutual inhibition during hypernatremia. They also demonstrate that the Fos-ir in the area postrema after intragastric osmotic loading is heavily dependent on the intact connectivity of the SFO.     

The depressive effect of Pi on the force-pCa relationship in skinned single muscle fibers is temperature dependent

Increases in P_i combined with decreases in myoplasmic Ca²⁺ are believed to cause a significant portion of the decrease in muscular force during fatigue. To investigate this further, we determined the effect of 30 mM P_i on the force-Ca²⁺ relationship of chemically skinned single muscle fibers at near-physiological temperature (30°C). Fibers isolated from rat soleus (slow) and gastrocnemius (fast) muscle were subjected to a series of solutions with an increasing free Ca²⁺ concentration in the presence and absence of 30 mM P_i at both low (15°C) and high (30°C) temperature. In slow fibers, 30 mM P_i significantly increased the Ca²⁺ required to elicit measurable force, referred to as the activation threshold at both low and high temperatures; however, the effect was twofold greater at the higher temperature. In fast fibers, the activation threshold was unaffected by elevating P_i at 15°C but was significantly increased at 30°C. At both low and high temperatures, 30 mM P_i increased the Ca²⁺ required to elicit half-maximal force (pCa₅₀) in both slow and fast fibers, with the effect of P_i twofold greater at the higher temperature. These data suggest that during fatigue, reductions in the myoplasmic Ca²⁺ and increases in P_i act synergistically to reduce muscular force. Consequently, the combined changes in these ions likely account for a greater portion of fatigue than previously predicted based on studies at lower temperatures or high temperatures at saturating Ca²⁺ levels. force-pCa relationship; phosphate; fatigue