Capillarity, Fibre Types and Fibre Morphometry in Different Sampling Sites across and along the Tibialis anterior Muscle of the Rat

Abstract

Capillarity, fibre types, fibre cross-sectional areas and perimeters were studied along and across the rat tibialis anterior muscle. The muscle was sectioned at three different levels (proximal, equatorial and distal) choosing five sampling fields for measurements at each level (from anterior to posterior and lateral to medial zones). Significant differences were found in the percentage of fibre types and capillarity between different fields of the same muscle section. Slow oxidative fibres were confined to the posterior muscle zone with a maximum of 3.7%. The posterior fields also had a greater percentage of fast oxidative glycolytic fibres at proximal (72.3%) and equatorial (61.3%) levels, but a lower value at the distal level (44.8%) and lower capillary density counts in total cross-section means (758 vs. 1,069 capillaries/mm² in equatorial and 1,035 capillaries/mm² at proximal levels). The uneven distribution of both fast fibre types and the different degrees of capillarisation along the muscle are statistically significant and may be due to different biomechanical performances along the rat tibialis anterior. Fibre size was significantly larger at the distal level, but no morphometric differences were found across the section of the same level. At the distal level, the mean total fibre area of fast glycolytic fibres (5,130 μm²) and fast oxidative glycolytic fibres (2,493 μm²) contrasted with values at the proximal (fast glycolytic: 4,070 μm², fast oxidative glycolytic: 1,970 μm²) and equatorial (fast glycolytic: 3,535 μm², fast oxidative glycolytic: 1,714 μm²) levels. The differences along and across the muscle show the need to design a standardised procedure for sample location when performing comparative studies of morphofunctional adaptive changes in skeletal muscle. A significant difference between individuals (animals) in all parameters was evident and should be taken into consideration when analysing the variability: the factor ‘animal’ should be considered in multiway ANOVAs, especially when low sample sizes are used.

Heterogeneous oxygenation in nonexercising triceps surae muscle during contralateral isometric exercise

“…Laughlin and Armstrong (1982) demonstrated that adrenergic vasoconstriction is greater in low-oxidative, fast-twitch skeletal muscle than in high-oxidative muscle at rest and during exercise. In animals, the proximal portion of the skeletal muscle contains a higher percentage of slow oxidative fibers than the distal portion (Torrella et al 2000;Wang and Kernell 2000). Johnson et al (1973) reported that muscle fiber type composition is similar in the medial and lateral heads of the gastrocnemius muscle.…”

Capillary supply, fibre types and fibre morphometry in rat tibialis anterior and diaphragm muscles after intermittent exposure to hypobaric hypoxia

“…Since rat TA (Torrella et al 2000) and DG (Green et al 1984) muscle Wbre is heterogeneous, several Welds or sample zones were selected from each muscle. The equatorial zone of the TA was analysed using Wve Welds from the cross-sectional area following the protocol described in Torrella et al (2000) as represented schematically in Fig.…”

“…The equatorial zone of the TA was analysed using Wve Welds from the cross-sectional area following the protocol described in Torrella et al (2000) as represented schematically in Fig. 2.…”

“…The former is responsible for inspiration (Sieck 1988), is continuously active and consists of three metabolically diVerent Wbre types (Powers et al 1990). The latter is a fast-contracting locomotory muscle that dorsiXexes the ankle (Ariano et al 1973) and also possesses a heterogeneous population of Wbre types (Torrella et al 2000). However, the TA has a diVerent activation pattern from the DG, since it is only active during locomotion and hence not active during hypobaric chamber conWnement.…”

Regional Differences in Blood Volume and Blood Transit Time in Resting Skeletal Muscle

“…In animal studies, the distal portion of skeletal muscle has a lower percentage of SO-type fibers than the proximal portion [8,9]. Regional differences in blood flow may reflect regional differences in the number of arterioles and/or capillaries, which may depend on the muscle fiber types [1].…”