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Muscle fibers from dysgenic mouse in vivo lack a surface component of peripheral couplings
C Franzini-Armstrong1, M Pincon-Raymond, F Rieger
1Department of Anatomy, University of Pennsylvania, Philadelphia, 19104-6058.
Abstract:
We have studied the structure of developing normal and dysgenic (mdg/mdg) mouse muscle fibers in vivo, with special attention to the components of the junctions between the sarcoplasmic reticulum and either the surface membrane or the transverse tubules. Triads and dyads are rare in dysgenic muscle fibers, but have apparently normal disposition of feet and calsequestrin. Peripheral couplings in normal developing muscle fibers have junctional tetrads in their surface membrane in association with the junctional feet. Muscle fibers in dysgenic mice lack junctional tetrads. This provides indirect evidence for the identification of the components of junctional tetrads with dihydropyridine receptors, which are known to be absent in dysgenic muscle fibers.
Insights
Developing mouse muscle fibers show fewer triads and dyads in dysgenic types. This study identifies junctional tetrads in normal muscle, suggesting a link to dihydropyridine receptors absent in dysgenic muscle.
Area of Science:
- Muscle biology
- Cellular structure
- Molecular physiology
Background:
- Muscle contraction relies on intricate structures like triads and dyads.
- Dysgenic mouse models offer insights into muscle development and function.
- The precise molecular composition of muscle cell junctions is crucial for excitation-contraction coupling.
Purpose of the Study:
- To investigate the structural organization of developing muscle fibers in normal and dysgenic mice.
- To identify the molecular components within the junctions of the sarcoplasmic reticulum and surface membranes.
- To elucidate the role of junctional tetrads in normal muscle fiber development.
Main Methods:
- In vivo study of developing normal and dysgenic (mdg/mdg) mouse muscle fibers.
- Microscopic analysis focusing on sarcoplasmic reticulum and associated membrane junctions.
- Comparative examination of triad, dyad, and tetrad structures.
Main Results:
- Triads and dyads are significantly reduced in dysgenic muscle fibers.
- Normal muscle fibers exhibit junctional tetrads at peripheral couplings.
- Dysgenic muscle fibers lack these junctional tetrads.
- Feet and calsequestrin show normal disposition in dysgenic muscle junctions.
Conclusions:
- Junctional tetrads are a feature of normal developing muscle fiber surface membranes.
- The absence of junctional tetrads in dysgenic muscle provides indirect evidence for their association with dihydropyridine receptors.
- This finding supports the identification of dihydropyridine receptors as components of junctional tetrads.