Immunohistochemical analysis of MCT1 and CD147 in equine skeletal muscle fibres

Monocarboxylate transporter 1 (MCT1) and its ancillary protein CD147 facilitate efflux of lactate from the muscle. Expression of MCT1 and CD147 were studied with immunohistochemistry in type I, IIA, IIAB and IIB fibres of equine gluteal muscle. Staining intensity of MCT1 in the cytoplasm as well as in the membranes of fibre types decreased in the order I = IIA > IIAB > IIB and correlated with the oxidative capacity. Capillaries were pronounced in the MCT1 staining. CD147 antibody stained plasma membranes of all fibre types evenly, whereas the staining in the cytoplasm followed that of MCT1. In the middle gluteal muscle the expression of MCT1 follows the oxidative capacity of muscle fibres, but the expression of CD147 in sarcolemma does not vary among fibre types. The use of horse specific MCT1 and CD147 antibodies can in future studies help to evaluate lactate efflux from different muscle fibre types.     

Effect of controlled exercise on middle gluteal muscle fibre composition in Thoroughbred foals

REASONS FOR PERFORMING STUDY: Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals. HYPOTHESIS: Well-controlled exercise could improve muscle potential ability for endurance running. METHODS: Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in each fibre type. RESULTS: All fibre types were hypertrophied with growth and type I and IIA fibres were significantly larger in the training than the control group at age 12 months. A significant increase of SDH activity was found in type IIX muscle fibres in the training group. CONCLUSIONS: Training in young Thoroughbred horses can facilitate muscle fibre hypertrophy and increase the oxidative capacity of type IIX fibres, which could potentially enhance stamina at high speeds. POTENTIAL RELEVANCE: To apply this result to practical training, further studies are needed to determine more effective and safe intensities of controlled exercise.     

Training and growth induced changes in the middle gluteal muscle of young Standardbred trotters

The middle gluteal muscle of five, two-year-old untrained trotters was investigated by repeated needle biopsy sampling over a training period of six months. A second group of five, three-year-old untrained horses was included to examine the effect of growth. After the training period increases were found in the relative distribution of slow twitch (ST) fibres from 18 per cent to 25 per cent and fast twitch (FTa) fibres from 36 per cent to 45 per cent, and a decrease in FTb fibres from 46 per cent to 30 per cent. A proportionally equal reduction (approximately 18 per cent) in the cross sectional area of all fibre types was observed after the first two months of training succeeded by an increase to approximately pretraining levels at the end of the period. The number of capillaries per fibre was enhanced from 1.7 to 2.4. Proliferation of capillaries occurred around fibres of all types. The metabolic adaptations showed increases in the activities of 3-hydroxy-acyl-CoA dehydrogenase (HAD) (50 per cent) and citrate synthase (31 per cent). Growth had no effect on the relative fibre type distribution nor the capillary per fibre ratio, but as the mean fibre area increased 36 per cent (primarily because of increases in FT fibres) the number of capillaries/mm2 was lower in the older untrained horses (350 capillaries/mm2) compared with the younger untrained ones (460 capillaries/mm2). Increase with growth was found in the activity of phosphorylase and HAD and a decrease was seen in the activity of hexokinase. It is concluded that the training programme exclusively induced alterations which improved the aerobic capacity of the muscle.     

Effects of a submaximal treadmill training programme on histochemical properties, enzyme activities and glycogen utilisation of skeletal muscle in the horse

The effects of training on skeletal muscle composition were studied in four Standardbred geldings given a seven week submaximal treadmill training programme. Before the start of training, muscle biopsies were collected from the left middle gluteal muscle for the determination of muscle fibre types, oxidative capacity and capillary numbers using histochemical techniques. The concentrations of citrate synthase, 3-hydroxyacyl-CoA dehydrogenase (HAD), lactate dehydrogenase and total muscle glycogen were measured using fluorometric methods. Muscle biopsy samples were repeated after one, three, five and seven weeks of training and the same measurements performed. No significant changes were found in muscle fibre types or capillary numbers as a result of training, although there was an increase in the oxidative capacity of the Type IIB fibres after seven weeks training. After seven weeks of training there were also increases in the concentrations of citrate synthase and HAD and a decrease in lactate dehydrogenase. Before commencement of training the horses underwent a standardised submaximal exercise test and muscle glycogen concentrations were measured before and immediately after the exercise. This procedure was repeated after one, three, five and seven weeks of training. A progressive decrease in the rate of glycogen utilisation occurred throughout the period of training, which by seven weeks was 36 per cent lower than that before training.     

Recruitment pattern of muscle fibre type during high intensity exercise (60-100% VO2max) in thoroughbred horses

To consider the optimal training programme for Thoroughbred horses, we examined the recruitment pattern of muscle fibres including hybrid muscle fibres in well-trained Thoroughbred horses. The horses performed exercise at three different intensities and durations; i.e., 100% VO2max for 4 min, 80% and 60% VO2max for 8 min on a treadmill with 10% incline. Muscle samples were obtained from the middle gluteal muscle before, during (4 min at 80% and 60% VO2max), and after exercise. Four muscle fibre types (types I, IIA, IIA/IIX, and IIX) were immunohistochemically identified, and optical density of periodic acid Schiff staining (OD-PAS) in each fibre type, and the glycogen content of the muscle sample, were determined by quantitative histochemical and biochemical procedures. The changes in OD-PAS showed that the recruitment of all fibre types were identical at the final time stage of each exercise bout, i.e., 4 min running at 100% VO2max, and 8 min running at 80% and 60% VO2max. The changes in OD-PAS of type IIA/IIX fibre were very similar to those of type IIX fibre. The recruitment of these fibres were obviously more facilitated by 4 min running at 100% VO2max than by 4 min running at 80% or 60% VO2max. Short duration with high intensity exercise, such as 4 min running at 100% VO2max or 8 min running at 80% or 60% VO2max, is effective to stimulate type IIX fibre and IIA/IIX fibres that have the fastest speed of contraction.     

Muscle fibre type composition in untrained and endurance-trained Andalusian and Arab horses

Muscle biopsies were taken from the middle gluteal muscle of 68 stallions (52 Andalusian [AN] and 16 Arab [AR]) ranging from six to 12 years of age. Seventeen AN horses and eight AR horses were untrained, while the remainder underwent active endurance training for 6 months. Fifteen AN horses were moderately endurance-trained while the other 20 AN horses and eight AR horses were strongly endurance-trained. Percentages of type I and type II fibres were similar in all groups (P greater than 0.05). The group of horses with the hardest training had a higher percentage of type IIA fibres (AN P less than 0.01; AR P less than 0.02) and a lower percentage of type IIB fibres (P less than 0.05 for AN and AR) than the untrained horses. All trained horses had a higher percentage of type IIB oxidative fibres and a lower percentage of type IIB non-oxidative fibres than the untrained horses (P less than 0.01 for both). These results suggest that the proportions of type I and type II fibres are highly stable within a given breed, but the stimulus of training facilitates changes both in contractile properties and, particularly, in the oxidative capacity of type II subgroups.     

Skeletal muscle characteristics in young trained and untrained standardbred trotters.

Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters.     

Effects of a nine-month endurance training programme on muscle composition in the horse

Muscle biopsy samples were collected from the middle gluteal muscle of seven horses undergoing a nine-month endurance training programme. Samples were collected before the programme began and again after three, six and nine months of training. A fifth sample was collected three months after training ceased. Serial muscle sections were reacted histochemically for myosin adenosine triphosphatase after either acid (pH 4.3 and 4.6) or alkaline (pH 10.3) pre-incubation, and muscle fibres identified as type I, IIA, IIB or IIC. The oxidative capacity of individual fibres was assessed, using the reduced nicotinamide dinucleotide tetrazolium reductase stain, and the number of intermyofibrillar capillaries adjacent to each fibre was counted after staining, using the alpha-amylase periodic acid Schiff technique. Biochemical analyses involved the fluorometric measurement of the enzymes citrate synthase, 3-hydroxy acyl CoA dehydrogenase and lactate dehydrogenase as markers of end terminal oxidative, beta oxidative and glycolytic potential, respectively. There was an increase in the percentage of type IIB fibres having high nicotinamide dinucleotide tetrazolium reductase staining after three months training. This increase persisted throughout the period of training and during the period without training. There was an increase in the number of capillaries adjacent to type IIB fibres after six and nine months training. These had returned to near pre-training numbers after three months without training. There were increases in the activities of citrate synthase and 3-hydroxy acyl CoA dehydrogenase after three months training. The activities of both enzymes continued to rise throughout training and the highest activities were attained after nine months.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glycogen depletion patterns in horses performing maximal exercise

Muscle biopsy samples were collected from the left middle gluteal muscle of horses participating in competitive barrier trials. Twelve horses were biopsied the day before and within 30 minutes of completion of an 800 m barrier trial. A further six horses were sampled the day before, and within 30 minutes of, completion of a 1200 m barrier trial. Serial muscle sections were examined histochemically for myosin adenosine triphosphatase activity after acid preincubation, to demonstrate type I, IIA and IIB fibres. The glycogen content in the individual fibres was assessed using the periodic acid Schiff (PAS) reaction. Total glycogen in muscle was measured fluorimetrically after hydrolysis to glucose. Significant decreases in total muscle glycogen levels of 167.1 +/- 22.2 and 158.1 +/- 23.2 mmoles glucose units kg-1 (dry weight) (mean +/- standard error) occurred from pre- to post trial samples for horses in both 800 and 1200 m trials respectively. There were no significant differences between the decreases in total muscle glycogen from horses in either 800 m or 1200 m trials. In both 800 m and 1200 m trials there was a significant decrease in the percentage of type IIA and IIB fibres classified as having high PAS staining intensity, and a significant increase in the percentage of fibres classified as having medium staining intensity when samples taken after the trial were compared to those taken before the trial.     

Differences in Muscle Fiber Recruitment Patterns between Continuous and Interval Exercises

We evaluated differences in muscle fiber recruitment patterns between continuous and interval training to develop an optimal training program for Thoroughbred horses. Five well trained female thoroughbred horses (3–4 years old) were used. The horses performed two different exercises on a 10% inclined treadmill: 90%VO₂ max for 4 min (continuous) and 90% VO₂ max for 2 min × 2 times with 10-min interval (interval). Muscle samples were obtained from the middle gluteal muscle before and immediately after the exercises. Four muscle fiber types (type I, IIA, IIA/X, and IIX) were immunohistochemically identified, and the optical density of periodic acid Schiff staining (OD-PAS) in each fiber type and glycogen content of the muscle sample were determined by quantitative histochemical and biochemical procedures, respectively. No significant differences were found in the OD-PASs and glycogen contents between the continuous and interval exercises, but the decreases in OD-PAS of fast-twitch muscle fibers were obvious after interval as compared to continuous exercise. Interval exercise may be a more effective training stimulus for the glycolytic capacity of fast-twitch muscle fiber. The data about muscle fiber recruitment can provide significant insights into the optimal training program not only for thoroughbred horses, but also for human athletes.     

Maternal dietary linoleic acid supplementation promotes muscle fibre type transformation in suckling piglets

As meat quality is basically dependent on muscle fibre characteristics, it is important to know how muscle fibres are regulated and transformed. This study aimed to investigate the effect of maternal dietary supplementation on muscle fibre types using 3% saturated fatty acid (palmitic acid, PA) or 3% unsaturated fatty acid (linoleic acid, LA) from 80 days of gestation to the weaning of offspring (25 days post‐natal). The results indicated that higher mRNA levels of MyHCI type genes were found in the soleus muscles of piglets that suckled from LA‐supplemented sows than from PA‐supplemented sows. In addition, LA treatment increased the gene expression of the type I muscle fibre marker troponin I (p < 0.01), suggesting that LA promoted muscle fibre type transformation to type I fibres. Moreover, PGC‐1α (p < 0.01) and MEF2c (p < 0.05) mRNA levels were higher in the piglets from the LA treatment group than in those from the PA treatment group. Furthermore, LA supplementation also significantly increased AMP‐activated protein kinase (AMPK) mRNA levels (p < 0.05), which is an upstream regulator of PGC‐1α. Collectively, these findings demonstrated that maternal dietary LA supplementation promoted muscle fibre transformation to type I fibre and that this process may be mediated through an AMPK‐dependent pathway.     

Muscle fibre type distribution of the thoracolumbar and hindlimb regions of horses: relating fibre type and functional role

Background

Although the majority of equine muscles have a mixed fibre type distribution indicative of diverse functional roles, the predominance of a fibre type can indicate the primary function of a muscle. The deep epaxial musculature has an important role in core spinal stability in humans, reflected as a predominantly muscle fibre type (MFT) I or postural fibre type. The fibre type of the deep epaxial musculature has not been determined in horses. The objective of the study was to determine the MFT distribution in selected muscles of thoracolumbar and hindlimb region of horses. This included deep epaxial and hypaxial muscles that were hypothesised to have a postural stabilising role. A second objective was to examine differences in MFT distribution between horses bred for endurance (Arabian) and sprinting (Quarter horse). Muscle biopsy samples were obtained from selected thoracolumbar and hind limb muscles of 5 Quarter horses, 4 Arabians, and 2 Thoroughbreds. The myosin heavy chain distribution was determined by gel electrophoresis. Mann–Whitney rank test was used to compare the proportional MFT and differences between breeds.

Results

Mm. sacrocaudalis dorsalis medialis and diaphragm had the highest proportion of MFT-I. The remaining deep epaxial muscles and the hypaxial muscle m. psoas minor had approximately equal MFT I and II proportions. Mm. psoas major, iliocostalis, longissimus dorsi and the hind limb muscles contained mostly MFT-IIX. The fibre type distribution was similar between Arabians and Quarter horses, although Quarter horses had more MFT-IIX fibres in psoas major (P = 0.02) while Arabians had more MFT-I fibres in m. longissimus dorsi (P = 0.03).

Conclusions

The fibre type distribution of the deep epaxial muscles, mm psoas minor and diaphragm varied from approximately equal MFT-I and II proportions to predominantly MFT-I suggesting a postural stabilising role possibly important in core spinal stability. In contrast the fibre type proportions of mm psoas major, iliocostalis, longissimus dorsi and the hind limb muscles were mainly MFT-II suggesting a locomotory role. Knowledge of fibre type distribution in such a clinically important area can direct diagnosis, prevention and treatment of muscular or neuromotor dysfunction.     

Effect of different blood‐guided conditioning programmes on skeletal muscle ultrastructure and histochemistry of sport horses

The effects of three different blood‐guided conditioning programmes on ultrastructural and histochemical features of the gluteus medius muscle of 2‐year‐old sport horses were examined. Six non‐trained Haflinger horses performed three consecutive conditioning programmes of varying lactate‐guided intensities [velocities eliciting blood lactate concentrations of 1.5 (v_1.5), 2.5 (v_2.5) and 4 (v₄) mm respectively] and durations (25 and 45 min). Each conditioning programme lasted 6 weeks and was followed by a 5‐week resting period. Pre‐, post‐ and deconditioning muscle biopsies were analysed. Although training and detraining adaptations were similar in nature, they varied significantly in magnitude among the three different conditioning programmes. Overall, the adaptations consisted in significant increases in size of mitochondria and myofibrils, as well as a hypertrophy of myofibrillar ATPase type IIA muscle fibres and a reduction in number of type IIx low‐oxidative fibres. Together, these changes are compatible with a significant improvement in both muscle aerobic capacity and muscle strength. The use of v_1.5 and v_2.5 as the exercise intensities for 45 min elicited more significant adaptations in muscle, whereas conditioning horses at v₄ for 25 min evoked minimal changes. Most of these muscular adaptations returned towards the pre‐conditioning status after 5 weeks of inactivity. It is concluded that exercises of low or moderate intensities (in the range between v_1.5 and v_2.5) and long duration (45 min) are more effective for improving muscle features associated with stamina and power in sport horses than exercises of higher intensity (equivalent to v₄) and shorter duration (25 min).     

Fibre composition, enzyme activity and concentrations of metabolites and electrolytes in muscles of standardbred horses

LINDHOLM, ARNE and KARIN PIEHL: Fibre composition, enzyme activity and concentrations of metabolites and electrolytes in muscles of standardbred horses. Acta vet. scand. 1974, 15, 287–309. — Measurements of metabolites, electrolytes, water, RNA and protein concentrations, the activity of certain muscle enzymes (SDH and PFK) and muscle fibre composition were made on biopsy specimens from the gluteus medius muscle of 68 standardbred horses, ½ to 8 years old. The muscle fibres were classified in 3 major categories, slow twitch (ST), fast twitch and high oxidative (FTH) and fast twitch (FT) fibres. The percentage of FTH fibres was higher after the age of 4 years, averaging 54 %. ST fibres comprised 24 % and this value remained unchanged.Glycogen concentration increased with age and averaged 95 and 126 mmol × kg⁻¹ wet muscle in the youngest and oldest age groups, respectively. Lactate and pyruvate concentrations were markedly decreased, whereas ATP, CP, G-6-P and glucose were unaffected with age. Water content averaged 75 % in all age groups, whereas Na⁺ concentration increased, K⁺ concentration decreased and Mg²⁺ concentration remained unchanged with increasing age. SDH activity in ½- and 8-year old horses increased from 6.1 to 13.6 μmol × (g×min.)⁻¹. PFK activity reached a peak at the age of 4 years after which it declined.With the data presented as a background, measurements on muscle biopsies may be a new aid in diagnosing diseases in horses and even in evaluating treatment. Of special interest might be investigations of muscle biopsy specimens as a base in the formation of more adequate training methods in race-horses.electrolytes; fibre types; glycogen storage; horse skeletal muscle; phosphofructokinase; succinate dehydrogenase.     

Fibre types,enzyme activities and substrate utilisation in skeletal muscles of horses competing in endurance rides

Venous blood samples and middle gluteal muscle biopsies were obtained from 21 horses taking part in 100 km or 50 km endurance rides. Group A consisted of seven horses competing over 100 km (four horses completed the ride), Group B consisted of the six horses that were among the 10 best over 50 km while the other eight horses of Group C completed 50 km at a slower speed. Blood lactate, glycerol and creatine kinase increased in all groups while aspartate aminotransferase levels were higher only in Group A. No change was found in blood glucose in Groups B and C while horses in Group A had lower levels after the ride. Neither fibre composition, fibre areas nor enzyme activities differed between the groups. Intramuscular glycogen content was similar before the ride in all groups. After the ride glycogen had decreased only half as much in Group C as compared to Groups A and B. Group C had a higher intramuscular triglyceride content at rest than Group B. The greatest decrease in triglyceride content after the ride was found in Group C. In Groups A and B many Type I, IIA and IIB fibres were glycogen depleted after the ride while in Group C mainly Type I and some Type IIA fibres were depleted. The results of this study show that intramuscular carbohydrate and lipid stores are both important fuels during endurance rides.     

Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications

Reason for performing study: Studies are required to define more accurately and completely the neuroanatomy of the equine dorsal cricoarytenoid muscle as a prerequisite for developing a neuroprosthesis for recurrent laryngeal neuropathy. Objective: To describe the anatomy, innervation, fibre types and function of the equine dorsal cricoarytenoid muscle. Methods: Thirty‐one larynges were collected at necropsy from horses with no history of upper airway disease and 25 subjected to gross dissection. Thereafter, the following preparations were made on a subset of larynges: histochemical staining (n = 5), Sihler's and acetylcholinesterase staining for motor endplates (n = 2). An additional 6 larynges were collected and used for a muscle stimulation study. Results: Two neuromuscular compartments (NMC), each innervated by a primary nerve branch of the recurrent laryngeal nerve, were identified in all larynges. Stimulation of the lateral NMC produced more lateral displacement of the arytenoid cartilage than the medial NMC (P<0.05). The medial NMC tended to rotate the arytenoid cartilage dorsally. Motor endplates were identified at the junction of the middle and caudal thirds of each NMC. If fibre type grouping was present it was always present in both NMCs. Conclusions: The equine dorsal cricoarytenoid muscle has 2 distinct muscle NMCs with discrete innervation and lines of action. The lateral NMC appears to have a larger role in increasing cross‐sectional area of the rima glottidis. Potential relevance: This information should assist in planning surgical reinnervation procedures and development of a neuroprosthesis for recurrent laryngeal neuropathy.     

Muscle fibre traits as additional selection criteria for muscle growth and meat quality in pigs – results of a simulated selection

To estimate the direct and correlated responses in meatiness and meat quality, simulated selection was applied using one‐trait selection and index selection including muscle fibre traits. In a total of 2024 pigs of German Landrace, Large White, Leicoma, and Schwerfurter breeds, carcass composition, meat quality, and fibre characteristics of the M. longissimus lumborum were analysed and genetic parameters were calculated by using REML variance component estimation. Coefficients of heritability ranged from low to moderate (growth traits: h² = 0.22–0.32; meat quality traits: h² = 0.17–0.27; muscle fibre traits: h² = 0.12–0.20). The total fibre number and the frequency of white fibres correlated positively with live weight (r_g = 0.44 and 0.44, respectively) and with loin muscle area (r_g = 0.38 and 0.19, respectively) while the relationships to pH value and drip loss were not as close (r_g = ?0.29–0.19). Selection indices were constructed from live weight and muscle area, from pH value and drip loss, and from muscle structure traits. As expected, simulated selection for live weight or loin muscle area lead to direct positive effects but these were associated with negative effects on meat quality traits (selection intensities: SI = 0.1; 0.5). Using selection for an index from loin area and muscle structure (loin muscle area + total fibre number – frequency of white fibres – frequency of giant fibres) the adverse effect on meat quality was minimized (responses in pH value: ?0.05; ?0.01) or was changed towards desired direction (responses in drip loss: ?0.65%; ?0.26%). The results show that fibre characteristics of pig muscle can be used as selection criteria for simultaneous improvement of carcass composition and meat quality in pigs by including indices developed from performance and fibre traits.     

Oxidative capacity of skeletal muscle fibres in racehorses: histochemical versus biochemical analysis

The oxidative capacity of skeletal muscle fibre types was evaluated histochemically using the nicotinamide dinucleotide diaphorase (NADH-D) staining, and biochemically by measuring the activity of citrate synthase (CS) in both whole muscle samples and in pools of fibres of identified type. Duplicate determinations of the NADH-D staining pattern resulted in standard deviations (sd) between duplicates of 6 and 11 per cent for two observers. The NADH-D pattern was found to differ between observers. Duplicate determinations of CS activity in the same fibre pools resulted in an sd value of 2.9 mumol/g/min. Measurements of whole muscle CS activity did not provide information about the distribution of oxidative capacity among fibre types. The NADH-D stain and CS activity in fibre pools both showed that, in general, type I and IIA fibres had a higher oxidative capacity than type IIB fibres. Biochemical techniques also showed, however, that the CS activity in type I and IIA fibres of different horses could vary as much as twofold, whereas the NADH-D rating showed a high intensity staining for most type I and IIA fibres in all horses. Furthermore, type IIB fibres received a lower NADH-D rating than the other fibre types even when the CS activities were quite similar. For purposes of research, biochemical measurement of oxidative capacity in individual muscle fibre types provides valuable quantitative and comparative information. The ease of histochemical NADH-D staining in comparison to fibre dissections makes this technique more practical for routine estimates of the distribution of oxidative capacity among muscle fibres.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle fibre distribution in forelimb,hindlimb and trunk muscles in three bat species: The little Japanese horseshoe,greater horseshoe and Egyptian fruit

This study characterised muscle fibres in trunk, forelimb and hindlimb muscles of three bat species: little Japanese horseshoe (Rhinolophus cornutus), greater horseshoe (Rhinolophus ferrumequinum) and Egyptian fruit (Rousettus aegyptiacus). Twenty-seven muscles from trunk, forelimb and hindlimb were dissected, weighed and analysed by immunohistochemistry and sodium didecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and determined their cross-sectional areas (CSA). Results showed that Type IIa and Type IIa/x made the highest proportion of total muscle mass. Moderate proportion was formed by Type IIb. Type I and IIx appeared at very low levels in all bats. Type IIb was the only fibre type detected in patagial muscles in wing membrane of greater horseshoe while other fibre types were not observed. Type I muscle fibres were very few and appeared infrequently in fifteen muscles of Egyptian fruit and in only one muscle in each, greater horseshoe and little Japanese horseshoe. Type IIx was also detected in three muscles in greater horseshoe and only one muscle in Egyptian fruit but none in little Japanese horseshoe. The highest average CSA μm² was detected in Type IIb and values were 734.2μm² for LHB; 1537.9μm² for GHB and 1,720.9μm² for EFB. Lowest and undetermined values were observed for Type I and IIx. These data demonstrate that Type IIa, IIa/x and IIb form significant proportion of adult bat muscle mass and Type IIb is the largest fibre type. The distribution pattern is suggestive of specialised functions of the fibres in relation to orientation and speed of bats during flight.     

Comparative study of muscle fiber type composition in the middle gluteal muscle of andalusian, thoroughbred and arabian horses

Samples were taken from the right middle gluteal muscle of 25 Andalusian horses, 20 Thoroughbreds and 10 Arabian horses, all aged between 5-and 12-years-old and not involved in training. Histochemical analysis was carried out using myosin ATPase after acid preincubation (pH 4.4) and NADH-tr in order to determine the percentage of different fiber types. Statistical analysis showed highly significant differences (P<0.001) in the proportion of type 1 and type 2 fibers between breeds. The Thoroughbred was found to have a significantly higher proportion of type 2A fibers (P<0.001) than the other 2 breeds, although differences in the proportion of type 2B fibers in different breeds were not found to be statistically significant. The Andalusian horse was found to have a higher proportion of fast-twitch fibers of low oxidative capacity (type FT) than the other 2 breeds (P<0.001). These results not only confirm those obtained in previous studies of different breeds of horses, but highlight the histochemical differences in the skeletal muscle of breeds of great commercial and sporting interest in Spain.