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Insulin binding to individual rat skeletal muscles
D J Koerker1, I R Sweet, D G Baskin
1Department of Medicine, University of Washington, Seattle 98195.
The American Journal of Physiology
|October 1, 1990
Summary
Skeletal muscle exhibits significant variation in insulin binding, with slow-twitch oxidative muscles showing higher binding than fast-twitch glycolytic muscles. This heterogeneity in insulin binding is due to differences in binding affinity and site number, not fiber type alone.
Area of Science:
- Endocrinology
- Muscle Physiology
- Biochemistry
Background:
- Previous studies suggested differences in insulin binding between red and white skeletal muscle.
- These studies often used whole muscle incubations or isolated membrane preparations.
Purpose of the Study:
- To investigate insulin binding heterogeneity across various rat skeletal muscles using unfixed cryostat sections.
- To determine if fiber type correlates with specific insulin binding parameters.
Main Methods:
- Autoradiography and computer-assisted densitometry were used to measure insulin binding in skeletal muscle slices.
- Displacement curves were analyzed using Scatchard plots to determine binding affinity and capacity.
Main Results:
- A 4.5-fold range in specific insulin binding was observed, with heart and slow-twitch oxidative muscles showing the highest binding.
- Dissociation constants (affinity) varied ninefold, and binding capacity showed significant differences between muscles.
- Neither binding affinity nor capacity correlated with fiber type or overall insulin sensitivity.
Conclusions:
- Considerable heterogeneity exists in insulin binding among rat hindlimb skeletal muscles.
- This heterogeneity arises from variations in both the affinity and number of insulin binding sites.
- Insulin binding parameters are not uniquely determined by a muscle's fiber type.