Primary skeletal muscle cells cultured on gelatin bead microcarriers develop structural and biochemical features characteristic of adult skeletal muscle

A primary skeletal muscle cell culture, in which myoblasts derived from newborn rabbit hindlimb muscles grow on gelatin bead microcarriers in suspension and differentiate into myotubes, has been established previously. In the course of differentiation and beginning spontaneous contractions, these multinucleated myotubes do not detach from their support. Here, we describe the development of the primary myotubes with respect to their ultrastructural differentiation. Scanning electron microscopy reveals that myotubes not only grow around the surface of one carrier bead but also attach themselves to neighbouring carriers, forming bridges between carriers. Transmission electron microscopy demonstrates highly ordered myofibrils, T-tubules and sarcoplasmic reticulum. The functionality of the contractile apparatus is evidenced by contractile activity that occurs spontaneously or can be elicited by electrostimulation. Creatine kinase activity increases steadily until day 20 of culture. Regarding the expression of isoforms of myosin heavy chains (MHC), we could demonstrate that from day 16 on, no non-adult MHC isoform mRNAs are present. Instead, on day 28 the myotubes express predominantly adult fast MHCIId/x mRNA and protein. This MHC pattern resembles that of fast muscles of adult rabbits. In contrast, primary myotubes grown on matrigel-covered culture dishes express substantial amounts of non-adult MHC protein even on day 21. To conclude, primary myotubes grown on microcarriers in their later stages exhibit many features of adult skeletal muscle and characteristics of fast type II fibers. Thus, the culture represents an excellent model of adult fast skeletal muscle, for example when investigating molecular mechanisms of fast-to-slow fiber type transformatio

Исследование взаимодействия депрессорных присадок и углеводородов дизельной фракции

В работе определены характеристики и состав образцов прямогонного дизельного топлива; приготовлены смеси образцов прямогонного дизельного топлива с депрессорными присадками, определены их низкотемпературные свойства; исследовано влияние депрессорных присадок на низкотемпературные свойства образцов прямогонного дизельного топлива; установлены закономерности влияния состава дизельного топлива на эффективность действия депрессорных присадок.In the course of the work, the characteristics and composition of straight-run diesel fuel samples were determined; mixtures of straight run diesel fuel samples with depressor additives were prepared, their low-temperature properties were determined; the effect of depressor additives on the low-temperature properties of straight-run diesel fuel samples was investigated; regularities of the influence of the composition of diesel fuel on the effectiveness of depressor additives were established

Influences on hypoxia exercise on whole body insulin sensitivity and oxidative metabolism in older individuals

Context Aging is a primary risk factor for most chronic diseases, including type 2 diabetes. Both exercise and hypoxia regulate pathways that ameliorate age-associated metabolic muscle dysfunction. Objective We hypothesized that the combination of hypoxia and exercise would be more effective in improving glucose metabolism than normoxia exercise. Design and Participants We randomized 29 older sedentary individuals (62 ± 6 years; 14 women, 15 men) to bicycle exercise under normobaric hypoxia (fraction of inspired oxygen = 15%) or normoxia (fraction of inspired oxygen = 21%). Intervention Participants trained thrice weekly for 30 to 40 minutes over 8 weeks at a heart rate corresponding to 60% to 70% of peak oxygen update. Main Outcome Measures Insulin sensitivity measured by hyperinsulinemic-euglycemic glucose clamp and muscle protein expression before and after hyperinsulinemic-euglycemic glucose clamp. Results Heart rate and perceived exertion during training were similar between groups, with lower oxygen saturation when exercising under hypoxia (88.7 ± 1.5 vs 96.2 ± 1.2%, P < 0.01). Glucose infusion rate after 8 weeks increased in both the hypoxia (5.7 ± 1.1 to 6.7 ± 1.3 mg/min/kg; P < 0.01) and the normoxia group (6.2 ± 2.1 to 6.8 ± 2.1 mg/min/kg; P = 0.04), with a mean difference between groups of –0.44 mg/min/kg; 95% CI, –1.22 to 0.34; (P = 0.25). Markers of mitochondrial content and oxidative capacity in skeletal muscle were similar after training in both groups. Changes in Akt phosphorylation and glucose transporter 4 under fasting and insulin-stimulated conditions were not different between groups over time. Conclusions Eight weeks of hypoxia endurance training led to similar changes in insulin sensitivity and markers of oxidative metabolism compared with normoxia training. Normobaric hypoxia exercise did not enhance metabolic effects in sedentary older women and men beyond exercise alone