Differentiation of rat skeletal muscle fibres during development and ageing
Karla Punkt1, Andreas Naupert, Gerhard Asmussen
1Institute of Anatomy, University of Leipzig, Liebigstrasse 13, Leipzig D-04103, Germany. punktk@medizin.uni-leipzig.de
Insights
Skeletal muscle fiber types and subtypes emerge by postnatal day 21 in rats. Metabolic and contractile activities peak at weaning, preparing muscle for increased demands.
Area of Science:
- Muscle physiology
- Developmental biology
- Histochemistry
Background:
- Skeletal muscle development involves differentiation of fiber types and metabolic profiles.
- Understanding the timeline of this differentiation is crucial for studying muscle function and adaptation.
Purpose of the Study:
- To identify the developmental timeline for skeletal muscle fiber type and subtype detection in rats.
- To analyze fiber type-specific metabolic changes and population shifts during postnatal development.
Main Methods:
- Immunohistochemistry using myosin heavy chain (MHC) antibodies.
- Enzyme histochemistry to detect ATPase activity.
- Cytophotometry to assess metabolic enzyme activities (oxidative and glycolytic).
Main Results:
- No clear fiber differentiation before birth; initial typing possible at postnatal day 1 (PD 1).
- Fast fiber subtypes (IIA, IIB/IIX) identified by PD 21 based on ATPase activity.
- Metabolic differentiation (SO, FOG, FG) and peak activity observed at PD 21 (weaning).
- Shift from FOG to FG fibers observed during development, indicating increased glycolytic capacity.
Conclusions:
- Skeletal muscle fibers achieve mature typing and metabolic profiles by weaning (PD 21).
- This developmental stage prepares muscle for enhanced functional demands.
- Postnatal development involves significant fiber type population and metabolic shifts.
Abstract:
The purpose of the present study was to determine at which point in the period from embryonic day 21 up to postnatal day (PD) 75, the different fibre types and subtypes are detectable in rat extensor digitorum longus, soleus and gastrocnemius muscles using immunohistochemical, enzyme histochemical and cytophotometrical methods. Moreover, fibre type-specific changes in metabolic profile and changes in fibre type population during postnatal development were analysed. Before birth, no clear differentiation of fibre types was found. At PD 1, slow and fast fibres were typed by antibodies against neonatal, slow and fast myosin heavy chains (MHCs). At PD 8, the different ATPase activities of slow and fast MHCs after alkaline preincubation were detected histochemically. At PD 21, differences in acid stability of ATPase activity of fast MHC isoforms revealed the fast subtypes IIA and IIB (including IIX). At this age, also differences in metabolic properties (oxidative and glycolytic enzyme activities) of fibres were detected for the first time by cytophotometry classifying the fibres into SO, FOG I, FOG II and FG. Before the age of 21 days, the fast fibres were metabolically undifferentiated. During further development and ageing, the population of FG fibres with high glycolytic activity increased at the expense of FOG fibres suggesting FOG to FG transformation. Cytophotometrical measurements revealed that the muscle fibres developed their highest contractile, oxidative and glycolytic activity at PD 21, the time of weaning. In this way, muscle fibres may be prepared for the higher demands for posture and mobility after leaving the nest.
