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PubMed1989

Selective in vitro reversal of the insulin resistance of glucose transport in denervated rat skeletal muscle.

Denervation (24 h) of skeletal muscle causes severe postreceptor insulin resistance of glucose transport and glycogen synthesis that is demonstrable in isolated muscles after short (30 min) preincubations. After longer preincubations (2-4 h), the insulin response of glucose transport increased to normal, whereas glycogen synthesis remained insulin resistant. Basal and insulin-stimulated amino acid transport were significantly lower in denervated muscles than in controls after short or long incubations, although the percentage stimulation of transport by insulin was not significantly different. The development of glucose transport insulin resistance after denervation was not attributable to increased sensitivity to glucocorticoids or adenosine. The selective in vitro reversal of glucose transport insulin resistance was not dependent on medium composition, did not require protein or prostaglandin synthesis, and could not be attributed to release of a positive regulator into the medium. The data suggest 1) the insulin receptor in muscle stimulates glucose transport by a signaling pathway that is not shared by other insulin-sensitive effector systems, and 2) denervation may affect insulin receptor signal transduction at more than one site.

Adenosine↗
PubMed1997

Expression of different isoforms of nitric oxide synthase in experimentally denervated and reinnervated skeletal muscle.

Denervated muscle fibers express enhanced levels of stress and apoptosis-associated proteins and undergo apoptosis. In experimentally denervated and reinnervated rat facial muscle, we now evaluate changes in the expression patterns of different isoforms of nitric oxide synthase (NOS)-generating nitric oxide (NO), which mediates oxidative stress and apoptosis. Physiological expression of NOS corresponds to a constant sarcolemmal staining pattern for neuronal NOS (nNOS) and a patchy sarcolemmal and weak sarcoplasmic labeling for the endothelial NOS-isoform, with no expression for inducible NOS (iNOS). Denervated muscle displayed distinct downregulation of nNOS with preserved expression of dystrophin. Also, denervated and immediately reinnervated muscle fibers showed decreased expression of nNOS. However, muscle fibers reinnervated for 10 weeks revealed a restored physiological expression of nNOS. There were no changes in the expression of endothelial and inducible NOS. As NO is known to induce growth arrest and collapse of neuronal growth cones, downregulation of NOS may contribute to promotion of axonal regeneration by aiding formation of new endplates. NO is upregulated in reinnervated muscle fibers and thus prevents polyneural hyperinnervation by extrajunctional synapses. Furthermore, downregulation of NOS during denervation is compatible with the finding that low levels of NO contribute to apoptosis instead of necrosis in disease states of oxidative stress.

Animals↗
PubMed1999

Matrix metalloproteinases MMP-2, MMP-7 and MMP-9 in denervated human muscle.

Proteolytic enzyme expression was studied by matrix metalloproteinases (MMP) immunoreactivity (-IR) in muscle biopsies from patients with amyotrophic lateral sclerosis (ALS), spinal muscle atrophy (SMA) and chronic axonal neuropathies (CANP). In normal muscle MMP-2-, MMP-7-, and MMP-9-IR was localized at neuromuscular junctions, in vessels and nerve branches. ALS biopsies of clinically non-affected muscles revealed neither MMP-2, -7-IR nor MMP-9-IR in atrophied myofibers. ALS-affected biopsies revealed MMP-9-IR, and to lesser extent MMP-2- and MMP-7-IR at normal sized and atrophied myofibers. Biopsies of SMA showed MMP-9- and MMP-7-IR at normal sized and atrophic myofibers, while MMP-2-IR was undetectable. In CANP MMP-9-IR was found at normal sized and atrophied myofibers. Distinct expression patterns of MMPs may thus reflect different stages of muscle denervation atrophy.

Adult↗
PubMed1988

Permeability to Ca2+ of the acetylcholine receptor channel of denervated mouse muscles in the presence of Na+ and of some other cations.

Calcium uptake caused by exposure to azelainylcholine and the additional membrane slope conductance caused by the same agonist were compared in partially depolarized mouse soleus muscles denervated for 3-5 days. Ca uptake was estimated from the amount of 45Ca retained after a 2 min exposure to the tracer (1 min in the presence of azelainylcholine) and a subsequent 17 min period of tracer washout. The amount taken up in the presence of Na+ was 0.152 m mole/kg fresh muscle. The uptake was by about 60% higher when Na+ was replaced by N-methyl-D-glucamine. For 10 other monovalent cations Ca uptake was less than with Na. Ca uptake was not related to the molecular weight, size or structure of the cation. The slope conductance in the presence of 10 microM azelainylcholine was 4 microseconds and it was 21% of that value when Na+ was replaced by N-methyl-D-glucamine, i.e. conductance was decreased when Ca uptake was increased. This discrepancy points to a major difference in the way cations such as Ca2+ and K+ pass the receptor channel.

Animals↗
PubMed2003

The nifk gene is widely expressed in mouse tissues and is up-regulated in denervated hind limb muscle.

Denervation of skeletal muscle alters the expression of many genes, which may be important for establishing optimal conditions for reinnervation. Using the differential display technique we have attempted to discover neurally regulated genes in skeletal muscle. An mRNA that is up-regulated in denervated hind limb muscle was identified and cloned. The cDNA encodes an RNA-binding protein, which was discovered during the course of this work to be a nucleolar protein interacting with the fork-head associated domain of the proliferation marker protein Ki-67, and named NIFK. We show that the nifk gene is widely expressed in adult mouse tissues and that the expression is up-regulated in denervated hind limb muscle. No difference between expression in perisynaptic and extrasynaptic portions of muscle was observed. The widespread expression in adult tissues suggests that the NIFK protein has other functions in addition to its interaction with Ki-67, which is only expressed in proliferating cells.

3' Untranslated Regions↗
PubMed1975

The possible role of cyclic AMP in the neurotrophic control of skeletal muscle.

1. Motoneurones provide trophic control of some of the functional characteristics of skeletal muscle fibres. This study has been designed to test whether the adenylate cyclase: cyclic AMP system may offer one potential mechanism for the mediation of neurotrophic regulation. 2. The concentration of cyclic AMP was measured at various intervals after muscle denervation. Muscle cyclic AMP concentration increases for the first 2 days after nerve section. It reaches a maximum value at 48 h and subsequently returns to the control value at 7 days. 3. Cyclic AMP concentration is unchanged by muscle disuse for the first 3 days following limb immobilization. Four days after immobilization, however, cyclic AMP increases in both the disused and contralateral control muscles. This phenomenon has been tentatively ascribed to some aspect of the inflammatory response. 4. Changing the level of nerve section, and therefore the length of the residual nerve stump, changes the temporal pattern of the increase in muscle cyclic AMP concentration. 5. Reinnervation of a denervated muscle produces a decrease in muscle cyclic AMP concentration. 6. It is concluded from the results that some aspect of nerve function provides trophic regulation of the muscle adenylate cyclase: cyclic AMP system. The mechanisms by which this regulation may be applied are considered in the Discussion.

Adenylyl Cyclases↗
PubMed1995

The ability to re-express polysialylated NCAM in soleus muscle after denervation is reduced in aged rats compared to young adult rats.

The neural cell-adhesion molecule, NCAM, contains an unusual homopolymer of sialic acid units, polysialic acid. This carbohydrate seems to be involved in neurite outgrowth, bundling and branching, processes which are important during reinnervation. In aged rats, reinnervation of denervated muscle fibres is incomplete. In this study, age-related changes in the degree of polysialylation of NCAM re-expressed after denervation were examined using a monoclonal antibody recognizing polysialic acid and a polyclonal antibody recognizing NCAM. The results show that, after denervation, the degree of polysialylation on NCAM was clearly reduced in rat soleus muscle of aged, compared to young, adult rats. This age-related change in expression of polysialic acid probably influences the reinnervation process in aged muscle.

Animals↗
PubMed2002

Alterations of nPKC distribution, but normal Akt/PKB activation in denervated rat soleus muscle.

Denervation has been shown to impair the ability of insulin to stimulate glycogen synthesis and, to a lesser extent, glucose transport in rat skeletal muscle. Insulin binding to its receptor, activation of the receptor tyrosine kinase and phosphatidylinositol 3'-kinase do not appear to be involved. On the other hand, it has been shown that denervation causes an increase in the total diacylglycerol (DAG) content and membrane-associated protein kinase C (PKC) activity. In this study, we further characterize these changes in PKC and assess other possible signaling abnormalities that might be related to the decrease of glycogen synthesis. The results reveal that PKC-epsilon and -theta;, but not -alpha or -zeta, are increased in the membrane fraction 24 h after denervation and that the timing of these changes parallels the impaired ability of insulin to stimulate glycogen synthesis. At 24 h, these changes were associated with a 65% decrease in glycogen synthase (GS) activity ratio and decreased electrophoretic mobility, indicative of phosphorylation in GS in muscles incubated in the absence of insulin. Incubation of the denervated soleus with insulin for 30 min minimally increased glucose incorporation into glycogen; however, it increased GS activity threefold, to a value still less than that of control muscle, and it eliminated the gel shift. In addition, insulin increased the apparent abundance of GS kinase (GSK)-3 and protein phosphatase (PP)1 alpha in the supernatant fraction of muscle homogenate to control values, and it caused the same increases in GSK-3 and Akt/protein kinase B (PKB) phosphorylation and Akt/PKB activity that it did in nondenervated muscle. No alterations in hexokinase I or II activity were observed after denervation; however, in agreement with a previous report, glucose 6-phosphate levels were diminished in 24-h-denervated soleus, and they did not increase after insulin stimulation. These results indicate that alterations in the distribution of PKC-epsilon and -theta; accompany the impairment of glycogen synthesis in the 24-h-denervated soleus. They also indicate that the basal rate of glycogen synthesis and its stimulation by insulin in these muscles are diminished despite a normal activation of Akt/PKB and phosphorylation of GSK-3. The significance of the observed alterations to GSK-3 and PP1 alpha distribution remain to be determined.

Animals↗
PubMed1983

Recovery from decamethonium in rat muscle and denervated guinea-pig diaphragm.

1. In denervated guinea-pig diaphragm the depolarization produced by decamethonium (100 microM) was followed by an initial phase of recovery, and then by a slow restoration of membrane potential in the presence of the drug, with hyperpolarization. Membrane potentials were measured by repeated insertions. The slow phase of spontaneous recovery was not found in the absence of potassium or in the presence of ouabain (100 microM). 2. With 1 microM-decamethonium the net loss of potassium from denervated muscle was 17% by wet weight in 20 min as compared with controls, which represents a loss of over 30 mM in internal concentration. Similar results were obtained with 100 microM-decamethonium. Spontaneous recovery of potassium occurred in the succeeding 2 h in the presence of 1 microM and 100 microM-decamethonium. With 5 nM-decamethonium muscles exposed for 20 min had a potassium content which was not reduced as compared with controls. 3. In rat diaphragm decamethonium (100 microM) also produced depolarization and slow spontaneous recovery which was not seen in the absence of potassium or the presence of ouabain. With 3 mM-decamethonium spontaneous recovery of potential was complete in 5 min. 4. Change from 5 mM-potassium to potassium-free solution produced consistent hyperpolarization in denervated guinea-pig diaphragm. In rat diaphragm at 38 degrees C the results were variable, with some fibres showing hyperpolarization while others showed depolarization.

Action Potentials↗