Responses of skeletal muscle protein turnover and amino acid concentration to unloading, denervation and immobilization.

Persistent Link:
http://hdl.handle.net/10150/184308
Title:
Responses of skeletal muscle protein turnover and amino acid concentration to unloading, denervation and immobilization.
Author:
Satarug, Soisungwan.
Issue Date:
1987
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The effects of denervation, non-weight bearing (unloading) or immobilization on hindlimb muscle growth, protein and amino acid metabolism were studied. In the first 3 days after denervation or unloading, atrophy of the soleus was caused by a suppression of protein synthesis and an acceleration of protein degradation. Thereafter, further atrophy, up to 6 days was due to depressed protein synthesis only. The changes in both protein synthesis and degradation in the first three days accounted for 69% and 65%, respectively, of the total loss of protein and mass in 6 days of unloaded or denervated soleus. Over the 6-day period, denervated soleus lost more mass and protein than the unloaded muscle owing to the earlier onset and greater extent of proteolysis. In denervated soleus, both lysosomal and non-lysosomal proteolysis may be enhanced, whereas in the unloaded muscle possibly only non-lysosomal proteolysis was enhanced. In both cases non-lysosomal proteolysis may be mediated by Ca²⁺-activated neutral protease, partially as a result of Ca²⁺ release from sarcoplasmic reticulum. Possibly due to the lack of lysosomal proteolysis, the insulin receptor did not show apparent increased turnover with unloading, as suggested by increased insulin sensitivity of in vitro protein turnover in the unloaded soleus. In contrast, denervated soleus showed a normal response to insulin for in vitro protein turnover. These findings suggested a mechanistic difference of unloading and denervation atrophy of soleus. A decreased ratio of glutamine/glutamate in fresh muscle suggested that the synthesis of glutamine in soleus may be diminished by denervation just as by unloading. This diminution of glutamine synthesis was probably due to reduced availability of ammonia, as evidenced by the slow disappearance of ATP in incubated denervated soleus. Similiar to unloading, denervation led to a decrease in aspartate concentration. This decreased concentration apparently resulted in decreased rather than increased utilization of aspartate. Effects of stretch on unloaded soleus were particularly pronounced in the first two days. Thereafter, in the stretched, unloaded soleus protein degradation increased to nearly the same extent as did protein synthesis. Hence after two days, stretch seems to lose its effectiveness in mitigating the effects of unloading so that it may not be an adequate preventive measure of muscle wasting under non-weight bearing condition.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Muscle proteins.; Muscles -- Growth.; Amino acids -- Metabolism.; Muscular atrophy.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Biochemistry; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Tischler, Marc E.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleResponses of skeletal muscle protein turnover and amino acid concentration to unloading, denervation and immobilization.en_US
dc.creatorSatarug, Soisungwan.en_US
dc.contributor.authorSatarug, Soisungwan.en_US
dc.date.issued1987en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe effects of denervation, non-weight bearing (unloading) or immobilization on hindlimb muscle growth, protein and amino acid metabolism were studied. In the first 3 days after denervation or unloading, atrophy of the soleus was caused by a suppression of protein synthesis and an acceleration of protein degradation. Thereafter, further atrophy, up to 6 days was due to depressed protein synthesis only. The changes in both protein synthesis and degradation in the first three days accounted for 69% and 65%, respectively, of the total loss of protein and mass in 6 days of unloaded or denervated soleus. Over the 6-day period, denervated soleus lost more mass and protein than the unloaded muscle owing to the earlier onset and greater extent of proteolysis. In denervated soleus, both lysosomal and non-lysosomal proteolysis may be enhanced, whereas in the unloaded muscle possibly only non-lysosomal proteolysis was enhanced. In both cases non-lysosomal proteolysis may be mediated by Ca²⁺-activated neutral protease, partially as a result of Ca²⁺ release from sarcoplasmic reticulum. Possibly due to the lack of lysosomal proteolysis, the insulin receptor did not show apparent increased turnover with unloading, as suggested by increased insulin sensitivity of in vitro protein turnover in the unloaded soleus. In contrast, denervated soleus showed a normal response to insulin for in vitro protein turnover. These findings suggested a mechanistic difference of unloading and denervation atrophy of soleus. A decreased ratio of glutamine/glutamate in fresh muscle suggested that the synthesis of glutamine in soleus may be diminished by denervation just as by unloading. This diminution of glutamine synthesis was probably due to reduced availability of ammonia, as evidenced by the slow disappearance of ATP in incubated denervated soleus. Similiar to unloading, denervation led to a decrease in aspartate concentration. This decreased concentration apparently resulted in decreased rather than increased utilization of aspartate. Effects of stretch on unloaded soleus were particularly pronounced in the first two days. Thereafter, in the stretched, unloaded soleus protein degradation increased to nearly the same extent as did protein synthesis. Hence after two days, stretch seems to lose its effectiveness in mitigating the effects of unloading so that it may not be an adequate preventive measure of muscle wasting under non-weight bearing condition.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectMuscle proteins.en_US
dc.subjectMuscles -- Growth.en_US
dc.subjectAmino acids -- Metabolism.en_US
dc.subjectMuscular atrophy.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineBiochemistryen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorTischler, Marc E.en_US
dc.contributor.committeememberWells, Michael A.en_US
dc.contributor.committeememberHaussler, Mark R.en_US
dc.contributor.committeememberBerry, James W.en_US
dc.contributor.committeememberGoll, Darrell E.en_US
dc.identifier.proquest8805527en_US
dc.identifier.oclc700280772en_US
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