Proportion Of Fast Glycolytic Fibers Research Articles

Morphology and fibre-type distribution in the tongue of the Pogona vitticeps lizard (Iguania, Agamidae).

Agamid lizards use tongue prehension for capturing all types of prey. The purpose of this study was to investigate the functional relationship between tongue structure, both surface and musculature, and function during prey capture in Pogona vitticeps. The lack of a detailed description of the distribution of fibre-types in the tongue muscles in some iguanian lizards has hindered the understanding of the functional morphology of the lizard tongue. Three methodological approaches were used to fill this gap. First, morphological analyses were performed (i) on the tongue surface through scanning electron microscopy, and (ii) on the lingual muscle by histological coloration and histochemistry to identify fibre-typing. Secondly, kinematics of prey capture was quantified by using high-speed video recordings to determine the movement capabilities of the tongue. Finally, electromyography (EMG) was used to identify the motor pattern tongue muscles during prey capture. Morphological and functional data were combined to discuss the functional morphology of the tongue in agamid lizards, in relation to their diet. During tongue protraction, M. genioglossus contracts 420 ± 96 ms before tongue-prey contact. Subsequently, Mm. verticalis and hyoglossus contract throughout tongue protraction and retraction. Significant differences are found between the timing of activity of the protractor muscles between omnivorous agamids (Pogona sp., this study) and insectivorous species (Agama sp.), despite similar tongue and jaw kinematics. The data confirm that specialisation toward a diet which includes more vegetal materials is associated with significant changes in tongue morphology and function. Histoenzymology demonstrates that protractor and retractor muscles differ in fibre composition. The proportion of fast glycolytic fibres is significantly higher in the M. hyoglossus (retractor muscle) than in the M. genioglossus (protractor muscle), and this difference is proposed to be associated with differences in the velocity of tongue protrusion and retraction (5 ± 5 and 40 ± 13 cm s(-1) , respectively), similar to Chamaeleonidae. This study provides a way to compare fibre-types and composition in all iguanian and scleroglossan lizards that use tongue prehension to catch prey.

Meta-analysis of the effect of animal maturity on muscle characteristics in different muscles, breeds, and sexes of cattle

The effect of animal maturity on fiber cross-sectional area, percentage of fiber types, activities of isocitrate dehydrogenase (ICDH) and lactate dehydrogenase (LDH), total and insoluble collagen and lipid concentration was investigated in the longis-simus thoracis (LT), semitendinosus (ST), and triceps brachii (TB) muscles. The analysis considered 2,642 muscle samples from bulls, steers, and cows of Aubrac, Charolais, Limousin, Montbéliard, and Salers breeds. For the bulls, the fiber cross-sectional area, percentage of slow oxidative fibers, and ICDH activity showed a quadratic relationship (P < 0.05), and the percentage of fast oxidative-glycolytic and fast glycolytic fibers and LDH activity showed a cubic relationship (P < 0.05) with increased maturity. A linear relationship was observed for the collagen and lipid muscle characteristics. The response equation coefficients for different muscles indicate that development of muscle characteristics is different for each muscle. Compared with the other muscles, ST muscle had a greater fiber cross-sectional area, proportion of fast glycolytic fibers, LDH activity, and collagen content. The LT muscle had a greater proportion of slow-oxidative fibers and lipid (P < 0.05). Within the ST muscle, all characteristics except lipid concentration showed different development between the breeds. Steers showed greater changes in muscle fiber cross-sectional area, percentage of fast oxidative-glycolytic and fast glycolytic fibers, and total lipid in the muscle with increasing maturity compared with bulls. The mean fiber cross-sectional area and percentage of fast glycolytic fibers was greater and the mean lipid concentration was less in bulls compared with steers (P < 0.05). Data for cows were from more mature animals. Muscle characteristics in cows did not show large changes with increasing degree of maturity. Muscle type accounts for a greater proportion of the variation in the muscle characteristics than breed and sex of the animal.

Metabolic response to halothane in piglets susceptible to malignant hyperthermia: an in vivo 31P-NMR study.

Using in vivo 31P-nuclear magnetic resonance spectroscopy, we studied the skeletal muscle metabolism of 17 anesthetized malignant hyperthermia-susceptible piglets and 25 control piglets during and after a halothane stress test. At rest, the phosphocreatine- (PCr) to-ATP ratio was 12% higher in the anesthetized piglets than in the control piglets, which may reflect a higher proportion of fast glycolytic fibers in the former. About 15 min of halothane administration sufficed to provoke onset of a reaction, which was characterized by a reciprocal drop in PCr and an increase in Pi with commencing intracellular acidosis. Halothane was withdrawn after a 20% drop in PCr. Within the next few minutes, intracellular pH dropped sharply and phosphomonoesters (PME) accumulated excessively. ATP was observed to decrease in 8 of the 17 animals. Halothane inhalation provoked a switch of metabolism toward glycolysis. Accumulation of PME suggests a mismatch between glycogenolysis and glycolysis. Despite severe acidification, glycolysis was not completely halted. Recovery of PCr and Pi started approximately 5 min after halothane withdrawal, with a longer time constant for recovery of the former. PME and intracellular pH aberrations lingered and started to recover later. Lost ATP was never restored within the observed recovery period of approximately 20 min.

Histochemical arguments for muscular non-shivering thermogenesis in muscovy ducklings.

1. The histochemical characteristics of gastrocnemius muscle were investigated in 6-week-old cold-acclimated (5 weeks, 4 degrees C) and glucagon-treated (5 weeks, 25 degrees C, 103 nmol/kg I.P. twice daily) muscovy ducklings, two groups able to develop non-shivering thermogenesis in vivo. A comparison was made with thermoneutral controls (25 degrees C) of the same age. All animals were fed ad libitum. Fibre type, fibre area and capillary supply have been studied. Further, a quantitative histochemical method for mitochondrial Mg(2+)-ATPase activity was developed to characterize the mitochondrial coupling state in situ. 2. White gastrocnemius was composed of fast glycolytic (FG) and fast oxidative glycolytic (FOG) fibres, while red gastrocnemius contained FOG and slow oxidative (SO) fibres. In white gastrocnemius, the proportion of FG fibres was higher in glucagon-treated than in control or cold-acclimated ducklings. In red gastrocnemius, the proportion of SO fibres was higher in both cold-acclimated and glucagon-treated ducklings than in controls. The area of all fibres was generally lower in glucagon-treated than in other ducklings. 3. The capillary density was higher in both red and white components of the gastrocnemius muscle in cold-acclimated and glucagon-treated than in control ducklings, as a result of an increased number of capillaries around each fibre. 4. In all fibres, except the FG type in cold-acclimated ducklings, the staining intensity of the Mg(2+)-ATPase reaction was higher in cold-acclimated and glucagon-treated than in control ducklings whereas the staining intensity with maximal decoupling of oxidative phosphorylation by dinitrophenol was unchanged. This indicated a more loose-coupled state of mitochondria in situ in all fibres of cold-acclimated ducklings, and in FOG fibres of white gastrocnemius and SO fibres of red gastrocnemius in glucagon-treated ducklings. 5. These results indicated a higher oxidative metabolism of skeletal muscle in both cold-acclimated and glucagon-treated than in control ducklings, and for most of the parameters studied, a similarity between cold acclimation and glucagon treatment. Because of the higher loose-coupled state of muscle mitochondria in cold-acclimated and glucagon-treated than in control ducklings, the higher oxidative capacity of skeletal muscle in these ducklings could be used for heat production rather than ATP synthesis and account for muscular non-shivering thermogenesis.

The effect of long-term high-frequency stimulation on capillary density and fibre types in rabbit fast muscles.

Rabbit fast muscles (tibialis anterior, t.a.; extensor digitorum longus, e.d.l.; and peroneal muscles) were stimulated for up to 28 days by electrodes implanted in the vicinity of the lateral popliteal (peroneal) nerve for 8 h/day, using either intermittent high-frequency (three trains at 40 Hz/min, each 5 s duration), or continuous stimulation at 10 Hz. This did not result in muscle hypertrophy even after 28 days. Capillary density (number of capillaries/mm2) was increased in e.d.l. from 251 +/- 3 to 366 +/- 6 after 14 days of stimulation and from 251 +/- 3 to 514 +/- 13 after 28 days of stimulation at 40 Hz. In t.a., capillary density increased from 373 +/- 5 to 583 +/- 10 after 14 days of stimulation at 40 Hz. The capillary/fibre ratio increased in e.d.l. from 1.25 +/- 0.02 to 1.86 +/- 0.04 at 14 days and to 2.07 +/- 0.06 at 28 days. In t.a., capillary/fibre ratio increased from 1.40 +/- 0.03 to 1.83 +/- 0.05 at 14 days. All these changes were significant (P less than 0.0005). Analysis of capillary density, capillary/fibre ratio, fibre areas and proportion of different fibre types in muscles stimulated for shorter periods showed no changes in capillary density, capillary/fibre ratio or fibre areas in e.d.l. or t.a. stimulated for 4 days; there was a decrease in the proportion of fast glycolytic fibres from 42 to 32% (P less than 0.0025) and increase in fast oxidative from 37.6 to 41.2% in e.d.l. Muscles stimulated for 7 days showed increases in capillary density and capillary/fibre ratio in fast predominantly glycolytic fibres in e.d.l., and a decrease in capillary density in fast and slow oxidative fibres in t.a. This was partly due to the increase in fibre areas in these groups (capillary/fibre ratio in t.a. was not significantly changed). No changes were observed in fibre areas in e.d.l. Stimulation at 10 Hz produced increase in capillary/fibre ratio in the vicinity of glycolytic fibres after only 4 days. High-frequency intermittent stimulation leads to a massive capillary growth which starts first in the muscle with a higher proportion of glycolytic fibres (e.d.l.), has a later onset than continuous low-frequency stimulation, and may be due to a combination of high blood flow and metabolic factors.

Protein synthesis versus energy state in contracting muscles of perfused rat hindlimb.

The goal of these studies was to evaluate acute changes in protein metabolism in skeletal muscle in response to contractile activity. Rates of protein synthesis were measured by following L-[U-14C]phenylalanine incorporation into protein in muscles of the perfused rat hindlimb at rest, during 10 min of maximal isometric muscle contractions, and during 10 min of recovery. Synthesis measurements were carried out under conditions that ensured that the specific radioactivity of the tRNA-bound precursor amino acid was equal to that of extracellular phenylalanine. Protein degradation was estimated by measuring the release of Nt-methylhistidine. Rates of synthesis were markedly inhibited in response to muscle contractions in tibialis anterior, gastrocnemius, and plantaris but were unaffected in soleus. Rates of synthesis returned toward those observed in the resting condition during the recovery period. Rates of degradation were also markedly inhibited in response to muscle contractions. Decreased rates of synthesis correlated with reduced tissue contents of ATP and creatine phosphate, a reduced ATP/ADP, and an elevated tissue content of lactate. The results demonstrate that isometric contractions in muscles consisting of a high proportion of fast glycolytic fibers result in a marked depression in rates of protein synthesis that may be due to an altered energy state.