AMP-deaminase activity in denervation atrophy of the amphibian skeletal muscle

The substrate (AMP) and co-factor (ATP)-dependent kinetic parameters of AMP-deaminase have been studied in the contralateral and denervated gastrocnemius muscles of frog, Rana hexadactyla. An increasing in apparent affinity (Km) and maximal velocity (V) were found with denervated muscle enzyme as compared to the contralateral muscle enzyme. The activation energy (delta E) values were found to be decreased on denervation suggesting increased catalytic efficiency of denervated muscle enzyme.     

Beta-adrenoceptor agonist treatment reverses denervation atrophy with augmentation of collagen proliferation in denervated mice gastrocnemius muscle

Daily oral administration of isoproterenol hydrochloride (60 mg/kg body weight; for 30 days) a beta-receptor agonist to normal innervated and denervated adult male Swiss albino mice confirmed its ability to induce skeletal muscle hypertrophy and reverse denervation atrophy respectively. Measurement of total tissue proteins and dry muscle mass showed 15-17% increase with 6% rise of hypertrophy index in gastrocnemius muscle. Hydroxyproline assay employed to measure the total tissue collagen exhibited 45% increase in collagen in normal innervated gastrocnemius muscle in response to beta agonist treatment. beta-adrenoceptor agonist ameliorated denervation atrophy along with further increase in collagen content of denervated gastrocnemius muscle.     

Increase in the amount of adenylate cyclase in rat gastrocnemius muscle after denervation

After section of the sciatic nerve, the basal adenylate cyclase (AC) activity in rat gastrocnemius muscle increased 6-7 times per membrane protein and about 2 times per whole muscle in the following 30 or 40 days. The AC activity in the muscle 30 days after denervation was increased about 4 times by forskolin. Calcitonin gene-related peptide (CGRP) also increased the adenylate cyclase activity in the denervated muscle. The binding of [3H]-forskolin (10nM) to cells isolated from gastrocnemius muscle was examined to determine the amount of AC molecules. Inhibition of [3H]-forskolin binding by increasing amounts of unlabeled forskolin gave a sigmoid curve with a IC50 value of 3 x 10(-7) M. Results showed that the number of [3H]-forskolin binding sites per cell was higher on the denervated side than on the control side, like the basal AC activity. The IC50 values for inhibition by unlabeled forskolin of binding of [3H]-forskolin were similar to muscles on the control and denervated sides. These results suggest that an increase in the AC activity induced by denervation was due to an increase in the numbers of AC molecules in the muscle.     

Effect of electropolarity treatment on activity levels of oxidative enzymes in gastrocnemius muscle of toad, Bufo melanostictus, during early stages of denervation

The activity levels of succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and cytochrome-C-oxidase showed a decrement whereas lactate dehydrogenase (LDH) evinced maximum activity during first 3 days of denervation. Under the impact of cathodal polarity treatment an elevation in the activity levels of these 4 enzymes was relatively more potent when compared to anodal polarity treatment. The role of polarity treatment in the regulation of these oxidative enzymes was discussed.     

Effect of molecular hydrogen saturated alkaline electrolyzed water on disuse muscle atrophy in gastrocnemius muscle

The objectives of this paper were to determine the level of oxidative stress in atrophied gastrocnemius, and to verify the effect of molecular hydrogen (H2) saturated alkaline electrolyzed water (HSW) on gastrocnemius atrophy by modifying the redox status, indicated by 8-hydroxy-2'-deoxyguanosine (8-OHdG), malondialdehyde (MDA), and superoxide dismutase (SOD)-like activity. Female Wistar rats were divided into four groups: (1) the control (CONT); (2) the Hindlimb unloading (HU, for 3 weeks) given purified normal water (HU-NW); (3) the HU given alkaline electrolyzed reduced water (HU-AEW); and (4) the HU given HSW (HU-HSW). We showed that 8-OHdG, but not MDA, significantly increased by 149% and 145% in HU-NW and HU-AEW, respectively, when compared with CONT. In contrast, there was a trend toward suppression in 8-OHdG levels (increased by 95% compared with CONT) by treatment of HSW, though this effect was not prominent. Additionally, SOD-like activity significantly increased in both HU-NW (184%) and HU-AEW (199%) when compared with CONT. This result suggests the elevation of O2-· in the atrophied gastrocnemius. However, upregulation of SOD-like activity in the HU-HSW was increased by only 169% compared with CONT, though this difference is too small to detect statistical significance. HU led to 13% and 15% reduction of gastrocnemius wet weights in HU-NW and HU-AEW, respectively, compared with CONT. And the reduction of gastrocnemius wet weights in HU-HSW was attenuated by 7% compared with CONT. The gastrocnemius wet weights in the HU-HSW group were significantly greater than those in the HU-AEW, but not statistically significant with HU-NW. These results indicate that HU causes an increase in oxidative stress, but, in this experimental protocol, continuous consumption of HSW during HU does not demonstrate successful attenuation of oxidative stress and HU-mediated gastrocnemius atrophy.     

Role of different proteolytic systems in the degradation of muscle proteins during denervation atrophy

In order to clarify the cellular mechanisms of denervation atrophy of skeletal muscle, we have studied protein turnover in denervated and control rat soleus muscles in vitro under different conditions. By 24 h after cutting the sciatic nerve, overall protein breakdown was greater in the denervated soleus than in the contralateral control muscle, and by 3 days, net proteolysis had increased about 3-fold. Since protein synthesis increased slightly following denervation, the rise in proteolysis must be responsible for the muscle atrophy and the differential loss of contractile proteins. Like overall proteolysis, the breakdown of actin (as shown by 3-methyl-histidine production by the muscles) increased each day after denervation and by 3 days was 2.5 times faster than in controls. Treatments that block the lysosomal and Ca2(+)-dependent proteolytic systems did not reduce the increase in overall protein degradation and actin breakdown in the denervated muscles (maintained in complete medium at resting length). However, the content of the lysosomal protease, cathepsin B, increased about 2-fold by 3 days after denervation. Furthermore, conditions that activate intralysosomal proteolysis (incubation without insulin or amino acids) stimulated proteolysis 2-3-fold more in the denervated muscles than in controls. Also, incubation conditions that activate the Ca2(+)-dependent pathway (incubation with Ca2+ ionophores or allowing muscles to shorten) were 2-3 times more effective in enhancing overall proteolysis in the denervated muscle. None of these treatments affected 3-methylhistidine production. Thus, multiple proteolytic systems increase in parallel in the denervated muscle, but a nonlysosomal process (independent of Ca2+) appears mainly responsible for the rapid loss of cell proteins, especially of myofibrillar components.     

Effect of increasing duration of denervation on the rate of entry of inorganic phosphate into rat gastrocnemius muscle.

The increased inorganic phosphate flow, characteristic of denervated gastrocnemius muscle, is shown to have no direct relation with either the loss of muscle mass or with the concentrations of the acid-soluble phosphate fractions. It is shown to increase hyperbolically with the time elapsed since the nerve section. The asymptotic value reached after thirty days suggests the presence of a saturable mechanism.