Abstract
The different bovine muscle fibre types I, IIA and IIX are characterised by their preferred metabolic pathway, either oxidative (I, IIA) or glycolytic (IIX), and their contraction speed, either slow-twitch (I) or fast-twitch (IIA, IIX). These physiological specificities are associated with variations in intracellular composition and their fluorescence spectra signatures. We hypothesised that these slight differences in autofluorescence responses could be used to discriminate the muscle fibre types by fluorescence imaging. Serial histological cross-sections of beef longissimus dorsi were performed: the start set was used to identify the metabolic and contractile type of muscle fibres by both immunohistoenzymology and immunohistofluorescence, and the following set was used to acquire synchrotron–deep ultraviolet (UV) autofluorescence images after excitation in the UV range (275 nm and 315 nm). This strategy made it possible to explore the label-free autofluorescence of muscle cells previously subtyped by histochemistry. Glycolytic cells (IIX) showed more intense fluorescence than oxidative cells (I and IIA) with near-90 % accuracy. This discrimination is more specifically assigned to the fluorescence of nicotinamide adenine dinucleotide. UV autofluorescence was unable to discriminate contractile type.
Highlights
Muscle is composed of elongated muscle cells that measure 10–100 μm in diameter but up to several centimetres in length.[1]
We have previously shown that type-dependent differences in muscle fibre intracellular composition change the optical properties of endogenous fluorophores naturally contained in biological cells.[13,14]
Connective tissue fluorescence The deep ultraviolet (DUV) fluorescence images (Figure 2, d–i) reveal fluorescent white lines that correspond to the arrays of connective tissue that make up the perimysium, perfectly identifiable after histological staining (Figure 2b and c)
Summary
Muscle is composed of elongated muscle cells that measure 10–100 μm in diameter but up to several centimetres in length.[1] They are usually called muscle fibres. These muscle fibres are wrapped in endomysium, a sheath of connective tissue composed of 90 % collagen with the remaining 10 % composed of other fibrous proteins, glycoproteins and proteoglycans.[2] Muscle fibres are characterised by their metabolic type (oxidative or glycolytic) and contraction rate (slow or fast-twitch).[3] There are three to four muscle fibre types depending.
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