Adaptive functional specialisation of architectural design and fibre type characteristics in agonist shoulder flexor muscles of the llama, Lama glama.

Like other camelids, llamas (Lama glama) have the natural ability to pace (moving ipsilateral limbs in near synchronicity). But unlike the Old World camelids (bactrian and dromedary camels), they are well adapted for pacing at slower or moderate speeds in high-altitude habitats, having been described as good climbers and used as pack animals for centuries. In order to gain insight into skeletal muscle design and to ascertain its relationship with the llama's characteristic locomotor behaviour, this study examined the correspondence between architecture and fibre types in two agonist muscles involved in shoulder flexion (M. teres major - TM and M. deltoideus, pars scapularis - DS and pars acromialis - DA). Architectural properties were found to be correlated with fibre-type characteristics both in DS (long fibres, low pinnation angle, fast-glycolytic fibre phenotype with abundant IIB fibres, small fibre size, reduced number of capillaries per fibre and low oxidative capacity) and in DA (short fibres, high pinnation angle, slow-oxidative fibre phenotype with numerous type I fibres, very sparse IIB fibres, and larger fibre size, abundant capillaries and high oxidative capacity). This correlation suggests a clear division of labour within the M. deltoideus of the llama, DS being involved in rapid flexion of the shoulder joint during the swing phase of the gait, and DA in joint stabilisation during the stance phase. However, the architectural design of the TM muscle (longer fibres and lower fibre pinnation angle) was not strictly matched with its fibre-type characteristics (very similar to those of the postural DA muscle). This unusual design suggests a dual function of the TM muscle both in active flexion of the shoulder and in passive support of the limb during the stance phase, pulling the forelimb to the trunk. This functional specialisation seems to be well suited to a quadruped species that needs to increase ipsilateral stability of the limb during the support phase of the pacing gait. Compared with other species, llama skeletal muscles are well suited for greater force generation combined with higher fatigue resistance during exercise. These characteristics are interpreted as being of high adaptive value, given the llama's habitat and its use as a pack animal.

Muscular partitioning in the semitendinosus muscle of the pig / Compartimientos musculares del músculo semitendinoso del cerdo

Neuromuscular compartments are subvolumens supplied by a primary nerve branch with homogeneous fiber characteristics. This muscular organization is important for understanding the muscle function in relation to postural and dynamic implications and also is relevant for appraising meat quality. Current researches associate fiber muscle characteristics with perimortem processes that regulate muscle transformation into meat. It is known that pig muscle has four heavy chain myosin isoforms: I, IIa, IIx and IIb. Castrated male pigs were slaughtered at 100 kg live weight. Semitendinosus muscle samples of each subvolumen determined previously (R1, R2, R3, R4) were frozen in liquid nitrogen and reacted for myofibrillar ATPase and NADH-TR for determining fiber types and oxidative capacity respectively. It were identified I, IIA and IIX/IIB fiber types. The frequency distribution of the I, IIA, and IIX/IIB fiber types were significantly greater in R1- R4, R4 and R3 respectively. The CSA of all fiber types was significantly larger in R1 than other compartments, notwithstanding CSA did not vary significantly among fiber types; oxidative capacity was significantly greater in R4. These results show a heterogeneousness of the muscle which would explain probably the disagreements documented between characteristics of fiber and meat quality traits.

Los compartimientos neuromusculares son subvolúmenes abastecidos por un ramo nervioso primario, los cuales poseen características fibrilares homogéneas. Esta organización muscular es importante para entender la función muscular en relación tanto en la estática y dinámica como en la apreciación de la calidad de la carne. Actuales investigaciones asocian características fibrilares con procesos perimorten que regulan la transformación del músculo en carne. Es conocido que en el músculo del cerdo están presentes cuatro cadenas pesadas de miosina: I, IIa, IIx y IIb. Cerdos machos castrados fueron faenados a los 100K kg de peso vivo. Muestras musculares de cada subvolumen del músculo semitendinoso, previamente determinados (R1, R2, R3, R4), fueron congeladas en nitrógeno líquido y tratadas con las reacciones de ATPasa miofribrilar y NADH-TR para determinar los tipos fibrilares y la capacidad oxidativa, respectivamente. Fueron identificadas los tipos fibrilares I, IIA y IIX/IIB. La frecuencia de distribución de los tipos fibrilares I, IIA, y IIX/IIB fueron significativamente mayores en R1- R4, R4 y R3, respectivamente. La CSA de todos los tipos fibrilares fueron significativamente mayores en R1 que en los otros compartimientos, sin embargo CSA no varía en forma significativa entre los tipos fibrilares; la capacidad oxidativa fue significativamente mayor en R4. Estos resultados evidencian una heterogeneidad muscular la cual podría probablemente explicar los desacuerdos documentados entre las características de las fibras y su relación con la evaluación de la calidad de la carne.

Neuromuscular partitioning, architectural design, and myosin fiber types of the M. vastus lateralis of the llama (Lama glama).

The llama (Lama glama) is one of the few mammals of relatively large body size in which three fast myosin heavy chain isoforms (i.e., IIA, IIX, IIB) are extensively expressed in their locomotory muscles. This study was designed to gain insight into the morphological and functional organization of skeletal musculature in this peculiar animal model. The neuromuscular partitioning, architectural design, and myosin fiber types were systematically studied in the M. vastus lateralis of adult llamas (n = 15). Four nonoverlapping neuromuscular partitions or compartments were identified macroscopically (using a modified Sihler's technique for muscle depigmentation), although they did not conform strictly to the definitions of "neuromuscular compartments." Each neuromuscular partition was innervated by primary branches of the femoral nerve and was arranged within the muscle as paired partitions, two in parallel (deep-superficial compartmentalization) and the other two in-series (proximo-distal compartmentalization). These neuromuscular partitions of the muscle varied in their respective architectural designs (studied after partial digestion with diluted nitric acid) and myosin fiber type characteristics (identified immunohistochemically with specific anti-myosin monoclonal antibodies, then examined by quantitative histochemistry and image analysis). The deep partitions of the muscle had longer fibers, with lower angles of pinnation, and higher percentages of fast-glycolytic fibers than the superficial partitions of the muscle. These differences clearly suggest a division of labor in the whole M. vastus lateralis of llamas, with deep partitions exhibiting features well adapted for dynamic activities in the extension of stifle, whereas superficial portions seem to be related to the antigravitational role of the muscle in preserving the extension of the stifle during standing and stance phase of the stride. This peculiar structural and functional organization of the llama M. vastus lateralis does not confirm the generalized idea that deep muscles or the deepest portions within the same muscles somehow develop postural and/or low-intensity isometric functions. Rather, it suggests a primacy of architecture over intramuscular location in determining fiber type composition and hence division of labor within the muscle. A compartmentalization in the distribution of the three fast-subtype fibers (IIA, IIX, and IIB) also occurred, and this could also be relevant functionally, since these fiber types differed significantly in size (IIA < IIX < IIB), oxidative capacity (IIA > IIX > IIB), and capillarization (IIA = IIX > IIB). Furthermore, a typical spatial pattern in fiber type distribution was encountered in llama muscle (i.e., fiber types were consistently ranked in the order I --> IIA --> IIX --> IIB from the center to the periphery of fascicles), suggesting again peculiar and not well understood functional adaptations in these species.

Fiber muscle types in adult female pigs as determined by combinating histochemical and immunohistochemical methods

Las fibras musculares esqueléticas del cerdo han sido tradicionalmente tipificadas como I, IIA y IIB, más sus formas híbridas, determinando la actividad de la enzima miosina ATPasa miofibrilar. Recientemente, la utilización de anticuerpos monoclonales contra isoformas de cadena pesada de miosina, electroforesis y estudios moleculares, han documentado la existencia, además, de la isoforma IIx. El objetivo de este estudio fue determinar la existencia de las isoformas de miosina, presentes en los distintos tipos fibrilares, utilizando técnics histoquímicas e inmunohistoquímicas combinadas, dentro de una unidad experimental compuesta por muestras musculares del M. longissimo del dorso, en cerdas de 150 kg promedio. Las muestras fueron obtenidas 45 minutos después de la faena, mediante escisión y congeladas en acetona enfriada con hielo seco. Cortes seriados de 10 µm de espesor fueron tratados por la técnicas de mATPasa modificada por Nwoye (1982), a pH 4,6, NADH-TR e inmunohistoquímica. Histoquímicamente fueron identificados cinco grupos de fibras: tipo I oscuras, IIA claras, y tres tipos intermedios. Los ensayos inmunohistoquímicos permitieron identificar las isoformas ß lenta I, IIa, IIx y IIb presentes en fibras de tipo I, IIA, IIX, IIB y un grupo híbrido IIAX