Intramuscular pressure,EMG and blood flow during low-level prolonged static contraction in man

Seven men performed one-legged isometric knee-extension at 5% MVC for 1 h. Intramuscular pressure increased with contraction from its resting value of 14 (2–31) mmHg. Some intramuscular pressure recordings stayed at an almost constant level throught the 1 h contraction, but most recordings showed large fluctuations from resting values up to 90 mmHg. The overall mean intramuscular pressure was twice the resting value. In some cases, EMG recordings confirmed that the changes in intramuscular pressure were related to alternating recruitment of various parts of the knee-extensors. Blood flow in the femoral vein increased within 3 min of 5% MVC to a level of 1.58 (1.25-2.22) 1 min^-1 and no significant changes occurred during the 1 h contraction. In two subjects blood flow was measured also in the recovery period, and this decreased almost immediately when the muscle relaxed. It is concluded that during low-level static contractions, the blood supply to the exercising muscle is maintained at a sufficiently high level, and that the alternating recruitment of muscle fibres may result in a heterogeneously distributed blood flow within the contracting muscle. Despite this the muscle was fatigued after the 1 h at 5 % MVC. The rating of perceived exertion (RPE) increased from 1.9 (1–3) at the beginning to 4.5(2–8) at the end of contraction, and MVC was decreased by 12% after the contraction.     

Spectral analysis of spontaneous contractions of the isolated portal vein of rats

Summary The spontaneous contractions of segments of rat portal veins have been examined in vitro under isotonic and isometric conditions. The power density spectra of recorded time series lasting 10–60 min were calculated. The spectra usually consist of harmonic frequency components. Only during shorter periods of analysis (10 min time series) we sometimes found additional non-harmonic components. All frequency components are proportionally shifted by changes of the bath temperature according to an average Q₁₀ of 2.0. Increase of the load decreases the frequency of the contractions.The results of the spectral analysis, indicating a preponderance of a single source of periodicity, were supported by direct evidence of a pacemaker region. By recording contractions after systematic dissections of the portal vein segment, we found that spontaneous activity is generated at the central end of the segment.This work was supported by the Austrian Research Fund     

Polyethylenes Having Well‐Defined Bimodal Molecular Weight Distributions Formed with Bis(phenoxy‐imine) Zr Complexes

Summary: Bis(phenoxy‐imine) Zr complexes with MAO activation can produce polyethylenes with well‐defined bimodal molecular weight distributions. Polymerization behavior indicates that minor changes in the ligand structures can have a significant effect on the modality of the resulting polyethylenes. Although there is no direct relationship between the bimodal catalytic behavior and the structure of a precatalyst complex in solution, a precatalyst complex having a methyl or methoxy group para to the phenoxy‐oxygen inclined to exhibit bimodal behavior whereas that with a pentafluorophenyl group on the imine‐nitrogen displayed unimodal behavior. Polymerization results suggest that bimodal behavior is linked to the presence of two kinds of cationic active species, which arise from different modes of ligand coordination. A qualitative correlation was found between the calculated amounts of possible cationic active species and the uni‐ and bimodal catalytic behavior. Based on the results obtained, we concluded that the bimodal polyethylenes are produced by two kinds of cationic active species having two available cis‐located sites with cis‐N, trans‐O and cis‐N, cis‐O arrangements. The results introduced herein are rare examples of the production of well‐defined bimodal polyethylenes using a single precatalyst.

Bis(phenoxy imine) Zr complexes can produce well‐defined bimodal polyethylenes.     

Low plasma glutamine in combination with high glutamate levels indicate risk for loss of body cell mass in healthy individuals: the effect of N-acetyl-cysteine

Skeletal muscle catabolism, low plasma glutamine, and high venous glutamate levels are common among patients with cancer or human immunodeficiency virus infection. In addition, a high glycolytic activity is commonly found in muscle tissue of cachectic cancer patients, suggesting insufficient mitochondrial energy metabolism. We therefore investigated (a) whether an anaerobic physical exercise program causes similar changes in plasma amino acid levels, and (b) whether low plasma glutamine or high glutamate levels are risk factors for loss of body cell mass (BCM) in healthy human subjects, i.e., in the absence of a tumor or virus infection. Longitudinal measurements from healthy subjects over longer periods suggest that the age-related loss of BCM occur mainly during episodes with high venous glutamate levels, indicative of decreased muscular transport activity for glutamate. A significant increase in venous glutamate levels from 25 to about 40 M was seen after a program of anaerobic physical exercise. This was associated with changes in T lymphocyte numbers. Under these conditions persons with low baseline levels of plasma glutamine, arginine, and cystine levels also showed a loss of BCM. This loss of BCM was correlated not only with the amino acid levels at baseline examination, but also with an increase in plasma glutamine, arginine, and cystine levels during the observation period, suggesting that a loss of BCM in healthy individuals terminates itself by adjusting these amino acids to higher levels that stabilize BCM. To test a possible regulatory role of cysteine in this context we determined the effect of N-acetyl-cysteine on BCM in a group of subjects with relatively low glutamine levels. The placebo group of this study showed a loss of BCM and an increase in body fat, suggesting that body protein had been converted into other forms of chemical energy. The decrease in mean BCM/body fat ratios was prevented by N-acetyl-cysteine, indicating that cysteine indeed plays a regulatory role in the physiological control of BCM.Abbreviations BCM Body cell mass - HIV Human immunodeficiency virus type 1 - NAC N-Acetyl-cysteine     

Changes in fibre-type composition and myosin heavy-chain IId isoform in rat soleus muscle during recovery period after hindlimb suspension

We examined the changes in myosin heavy-chain (HC) isoforms and fibre-type composition in rat soleus muscle using both myosin adenosine triphosphatase staining and sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE) analyses during the recovery period after 4 weeks of hindlimb suspension. Although there was no change in type IIc fibres after the suspension, an increase in this type of fibres was observed during the 1- to 4-week recovery period. The increase in type Ilc fibres was considered to be due to a shift from type Ila to IIc fibres. The SDS-PAGE analysis revealed the presence of the HC IId isoform, which was not observed in the control muscle, after a 4-week hindlimb suspension. The HC IId isoform gradually decreased over 3 weeks of recovery and disappeared in the 4th week of recovery after the suspension. These results suggest that the hypogravity conditions induced by hindlimb suspension stimulated the synthesis of the HC IId isoform, whereas an increase in mechanical load to the muscle accelerated the degradation of the HC IId isoform and the synthesis of type Ilc fibres during the recovery period after hindlimb suspension.     

Effect of different types of high carbohydrate diets on glycogen metabolism in liver and skeletal muscle of endurance-trained rats

Male Wistar rats were fed ad libitum four different diets containing fructose, sucrose, maltodextrins or starch as the source of carbohydrate (CH). One group was subjected to moderate physical training on a motor-driven treadmill for 10 weeks (trained rats). A second group received no training and acted as a control (sedentary rats). Glycogen metabolism was studied in the liver and skeletal muscle of these animals. In the sedentary rats, liver glycogen concentrations increased by 60%–90% with the administration of simple CH diets compared with complex CH diets, whereas skeletal muscle glycogen stores were not significantly affected by the diet. Physical training induced a marked decrease in the glycogen content in liver (20%–30% of the sedentary rats) and skeletal muscle (50%–80% of the sedentary rats) in animals fed simple (but not complex) CH diets. In liver this was accompanied by a two-fold increase of triacylglycerol concentrations. Compared with simple CH diets, complex CH feeding increased by 50%–150% glycogen synthase (GS) activity in liver, whereas only a slight increase in GS activity was observed in skeletal muscle. In all the animal groups, a direct relationship existed between tissue glucose 6-phosphate concentration and glycogen content (r = 0.9911 in liver, r = 0.7177 in skeletal muscle). In contrast, no relationship was evident between glycogen concentrations and either glycogen phosphorylase activity or adenosine 5-monophosphate tissue concentration. The results from this study thus suggest that for trained rats diets containing complex CH (compared with diets containing simple CH) improve the glycogenic capacity of liver and skeletal muscle, thus enabling the adequate regeneration of glycogen stores in these two tissues.     

The effect of hydrolytic enzymes on the acetylcholine sensitivity of the skeletal muscle cell membrane

Isometric tension developed by rat soleus and extensor digitorum longus (EDL) muscles in response to acetylcholine (Ach) applied in vitro was recorded. Tension of contractures elicited in response to Ach increased after muscles had been incubated with phospholipase C, pepsin, or soluble fractions prepared from muscle homogenate.Using intracellular microelectrodes, resting membrane potential (RMP) and depolarisation in response to Ach added to the bathing medium were recorded in endplate-free regions of the muscle fibres. No significant change in RMP was observed in muscles incubated with soluble muscle fraction or phospholipase C, but depolarisation in response to Ach or carbachol was significantly increased. The time course for the increase in depolarisation and the contracture response to Ach was similar.When all available receptors were blocked with -bungarotoxin prior to incubation so that no response to Ach could be elicited, with subsequent incubation in muscle soluble fraction or phospholipase C, both contractures and depolarisation in response to Ach returned. These results support the hypothesis that receptors, not previously available to interact with Ach or -bungarotoxin were revealed following incubation.     

Mobilization of free Ca2+ measured during contraction-relaxation cycles in smooth muscle cells of the porcine coronary artery using quin2

Ca²⁺ mobilization in dispersed smooth muscle cells of the porcine coronary artery was investigated using the fluorescent Ca²⁺ indicator, quin2. The resting [Ca²⁺]_i was 113±8 nM (a mean±SE), and was independent of intracellular quin2 concentrations. Acetylcholine (ACh; over 10 nM) or caffeine (over 3 mM) transiently increased the intensity of fluorescence, thereby reflecting the elevation of intracellular free Ca²⁺ (Ca²⁺ transient), while excess K⁺ gradually increased and maintained the intensity of fluorescence. Application of EGTA reduced the resting intensity of the fluorescence and blocked the K⁺-induced Ca²⁺ transient, but did not supress the Ach-or caffeine-induced ones. Nisoldipine (0.1 M) did not affect the resting intensity of the fluorescence. This agent blocked the K⁺ induced but not the ACh-or caffeine-induced Ca²⁺ transient. Thus, sources of Ca²⁺ contributing to the K⁺-induced Ca²⁺ transient differ from those evoked by other agents. The amount of Ca²⁺, as estimated from the increased Ca²⁺ transient by caffeine or ACh, was increased in proportion to the excess K⁺-induced influx of Ca²⁺.     

A cytoplasmic component of pyridine nucleotide fluorescence in rat diaphragm: evidence from comparisons with flavoprotein fluorescence

Pyridine nucleotide (PN) and flavoprotein (Fp) fluorescence were monitored in the isolated intact rat diaphragm. A substantial increase in PN fluorescence occurred when N₂ replaced O₂ in glucose medium. This response was much reduced in pyruvate medium and/or by pretreatment with iodoacetic acid (IAA). The anaerobic levels of Fp fluorescence were less affected by substrate and IAA. Substitution of glucose by pyruvate did not alter the PN fluorescence of the resting aerobic tissue, but increased Fp fluorescence. After a tetanus with glucose present the PN of the anaerobic muscle, but not the Fp underwent a substantial transient oxidation. This oxidation was absent in pyruvate medium. It is concluded that a cytoplasmic component of the PN fluorescence is present in skeletal muscle. The levels of Fp fluorescence in the resting and contracting aerobic tissue supplied with pyruvate suggest that the resting tissue respiration was ADP limited. On this basis the level of PN fluorescence in the aerobic resting state was less than expected; the source of the PN fluorescence was both mitochondrial and cytoplasmic.     

Autografting of whole muscles in reptiles

Autografting (reimplantation) of the whole gastrocnemius muscle was carried out in turtles (Testudo horsfieldi) weighing 300–500 g. The grafts were investigated 2 weeks to 6 months after transplantation. After 5–6 months the reimplanted muscles were similar in color and shape to the intact symmetrical muscles and they amounted to 77% of their weight. Regeneration was observed in the grafts, but its course was slower than in mammals. Separation of myoblasts from disintegrating muscle fibers of the graft took place rapidly during the first month and continued until 2 months after grafting. Simultaneously, differentiation of myogenic elements into cross-striated muscle fibers and vascularization of the grafts were observed. Most of the grafts by the end of the period of investigation had a muscular type of structure, although considerable variability was observed in the diameter of the muscle fibers.Laboratory of Evolutionary Histology, A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. P. Avtsyn.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 84, No. 7, pp. 94–97, July, 1977.