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Differential effects of acute changes in cell Ca2+ concentration on myofibrillar and non-myofibrillar protein breakdown in the rat extensor digitorum longus muscle in vitro. Assessment by production of tyrosine and N tau-methylhistidine.

ABSTRACT: The influence of Ca2+ on myofibrillar proteolysis was evaluated in the isolated extensor digitorum longus muscle incubated in vitro with agents previously shown to increase the intracellular concentration of Ca2+. Myofibrillar proteolysis was evaluated by measuring the release of N tau-methylhistidine, and total proteolysis was evaluated by measuring tyrosine release by incubated muscles after the inhibition of protein synthesis with cycloheximide. Incubated muscles released measurable quantities of N tau-methylhistidine, and muscle contents of the amino acids remained stable over 2 h of incubation. The release of N tau-methylhistidine by incubated muscles was similar to its release by perfused rat muscle in response to brief starvation, indicating the integrity of the incubated muscles. Ca2+ ionophore A23187, dibucaine, procaine, caffeine and elevated K+ concentration increased lactate release by incubated muscles and decreased tissue contents of ATP and phosphocreatine to varying degrees, indicating the metabolic effectiveness of the agents tested. Only A23187 and dibucaine increased total cell Ca2+, and they increased tyrosine release. Caffeine and elevated [K+] increased neither cell Ca2+ nor tyrosine release; however, only A23187 and dibucaine increased tyrosine release significantly. On the other hand, these agents were without effect on myofibrillar proteolysis as assessed by N tau-methylhistidine release by incubated muscles and changes in tissue contents of the amino acid. In fact, some of the agents tested tended to decrease myofibrillar proteolysis slightly. These results indicate that acute elevation of intracellular Ca2+ is associated with increased breakdown of non-myofibrillar but not myofibrillar proteins. Because of this, the role of elevated Ca2+ in muscle atrophy in certain pathological states is questioned. The data also indicate that the breakdown of myofibrillar and non-myofibrillar proteins in muscle is regulated independently and by different pathways, a conclusion reached in previous studies with perfused rat muscle.

SUBMITTER: Goodman MN

PROVIDER: S-EPMC1147533 | biostudies-other | 1987 Jan

REPOSITORIES: biostudies-other

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Project description:I. Experimental Design: a. Type of experiment: Time course b. Experimental factors: 3 month old mice subjected to lengthening contractions of the extensor digitorum longus muscle (EDL). Samples of EDL collected at 6 and 72 h and compared to non-treated control. c. How many hybridizations in exp: 9 d. Common reference used for all hyb: no e. Quality control steps: All arrays used from same lot. Triplicate hybridizations performed for each time point. II. Samples used, extracts, preparation and labeling: Animals. Nine male C57BL/6 mice (3-4 mo of age, 27.8 ± 3.3 g body mass, Harlan Sprague-Dawley, Indianapolis, IN). Muscle Injury. The extensor digitorum longus (EDL) muscle of six mice were exposed to lengthening contractions. Mice were anesthetized with 2% avertin (0.015 ml/kg) and supplemental doses were administered if the mouse responded to a toe pinch. Animals were placed on a plexiglass platform that was maintained at 37°C. The distal femur of the right hindlimb was fixed between screws and the foot was taped to the platform. The distal tendons of the EDL were exposed by incision and tied to the lever arm of a servomotor (Aurora Scientific, Richmond Hill ON, Canada) with 4-0 silk suture. Needle electrodes were placed adjacent to the peroneal nerve to stimulate dorsiflexor contraction (Grass Instruments, West Warwick, RI). Maximal isometric force (Po) was determined by stimulating the dorsiflexors maximally at optimum length (Lo) for force development. To induce muscle injury, 75 lengthening contractions were performed at 0.25 Hz for 5 min. For each lengthening contraction, the muscle was stimulated at 150 Hz and stretched 100 ms after the initiation of stimulation. Muscle stretch involved 20 % strain relative to Lo. Force deficit was evaluated 10 min after the 75 contractions and then the incision was closed with 7-0 silk suture. Animals were returned to their cage to recover until the time of sacrifice. Prior to sacrifice by cervical dislocation, animals were anesthetized with avertin and the EDL muscles were excised and flash frozen in liquid nitrogen. Muscles were stored in liquid nitrogen until RNA isolation. RNA Isolation. Total RNA was isolated from EDL muscles from control mice (n=3) and mice sacrificed at 6 h (n=3) and 72 h (n=3) after lengthening contractions according to the modified protocol of Chomzynski et al.. Frozen muscles were added to preweighed tubes containing TriReagent (Sigma-Aldrich, St. Louis, MO). Tissue was homogenized in TriReagent using a Tissue Tearor (Fischer, Pittsburgh, PA) at 30,000 rpm for 1 minute. Homogenates were transferred to sterile, RNAase free microcentrifuge tubes and incubated for 10 min at room temperature. Chloroform (0.2 ml; Sigma-Aldrich, St. Louis, MO) was added and after incubation, the samples were centrifuged for 15 min at 12,000 g and 4°C. Total RNA was precipitated from the aqueous phase by the addition of isopropanol (Sigma-Aldrich), and pelleted by centrifugation. Pellets were washed in ethanol (75 and 95 %) and air dried before resuspension in diethylpyrocarbonate (DEPC) treated water. RNA concentration was determined by optical density at 260 nm. III. Hybridization procedures and parameters: Microarray Hybridization and Analysis. To reduce measurement error, all membranes (Atlas mouse 1.2; Clontech, Palo Alto, CA) were prepared from the same lot. Additionally, each membrane was hybridized only once to avoid errors associated with stripping and multiple hybridizations. In order to minimize individual biological variability, total RNA was pooled from three animals for hybridization of arrays. Three arrays were used for the pooled sample at each time point. First strand cDNA probe generation from total RNA and microarray hybridization were performed according to manufacturer’s instructions (Atlas cDNA Expression Arrays User Manual, Clontech). 33P labeled cDNA was generated from sample RNA using [33P]-dATP (3000 Ci/mmol; ICN, Costa Mesa, CA) and Maloney murine leukemia virus (MMLV) reverse transcriptase (Clontech). Labeled probes were purified using nucleospin columns (Clontech). Array membranes were prehybridized in Express Hyb containing sheared Salmon testes DNA (Gibco BRL, Rockville, MD) for 30 min at 71°C in rotating hybridization tubes. Radiolabeled probe (3 x 106 cpm) was incubated in denaturing solution (Clontech) for 20 min at 71°C, after which Cot1 DNA/neutralizing solution was added and incubation continued for 10 min. The probe mixture was added to the hybridization tube and incubated with rotation overnight. Following hybridization, membranes were washed four times for 30 min in 2X saturated sodium citrate (SSC) and 1 % sodium dodecyl sulphate (SDS) at 71°C, once for 30 min in 0.1X SSC and 0.5% SDS at 71°C, and once for 5 min in 2X SSC at room temperature. Membranes were removed and immediately wrapped in plastic and exposed to a phosphor storage screen (Molecular Dynamics, Sunnyvale, CA) for four days. IV. Measurement data and specifications: Data Analysis. The membrane image was acquired using a Storm phosporimager (Molecular Dynamics) and Image Quant software. Array images were analyzed using Atlas Image 2.0 (Clontech) software to determine raw intensity levels of expression. Raw intensity data was imported into GeneSpring (Silicon Genetics, Redwood City, CA) expression analysis software. Intensity levels were normalized to the median expressed intensity on each of the arrays and averaged for the three arrays at each time point. Normalized expression levels for control arrays were established as a value of 1 and data from 6 and 72 h were expressed as fold changes relative to control. In order to simplify interpretation of the resulting dataset, a k-means cluster analysis was employed to group genes based on similarities in patterns of expression. To reduce the likelihood of false positives, the data was filtered using a criterion 2 fold change in expression prior to clustering. Miller et al. (61) have calculated that using an array of 10,000 features with a coefficient of variation (CV) of 20 percent, a 2 fold criterion for altered gene expression would result in zero false positives. The mean and median CV (15.8 and 14.3%, respectively) for all arrays in the current study fell within these guidelines for the elimination of false positives. Keywords: time-course

Project description:I. Experimental Design: a. Type of experiment: Time course b. Experimental factors: 3 month old mice subjected to lengthening contractions of the extensor digitorum longus muscle (EDL). Samples of EDL collected at 6 and 72 h and compared to non-treated control. c. How many hybridizations in exp: 9 d. Common reference used for all hyb: no e. Quality control steps: All arrays used from same lot. Triplicate hybridizations performed for each time point. II. Samples used, extracts, preparation and labeling: Animals. Nine male C57BL/6 mice (3-4 mo of age, 27.8 Â± 3.3 g body mass, Harlan Sprague-Dawley, Indianapolis, IN). Muscle Injury. The extensor digitorum longus (EDL) muscle of six mice were exposed to lengthening contractions. Mice were anesthetized with 2% avertin (0.015 ml/kg) and supplemental doses were administered if the mouse responded to a toe pinch. Animals were placed on a plexiglass platform that was maintained at 37Â°C. The distal femur of the right hindlimb was fixed between screws and the foot was taped to the platform. The distal tendons of the EDL were exposed by incision and tied to the lever arm of a servomotor (Aurora Scientific, Richmond Hill ON, Canada) with 4-0 silk suture. Needle electrodes were placed adjacent to the peroneal nerve to stimulate dorsiflexor contraction (Grass Instruments, West Warwick, RI). Maximal isometric force (Po) was determined by stimulating the dorsiflexors maximally at optimum length (Lo) for force development. To induce muscle injury, 75 lengthening contractions were performed at 0.25 Hz for 5 min. For each lengthening contraction, the muscle was stimulated at 150 Hz and stretched 100 ms after the initiation of stimulation. Muscle stretch involved 20 % strain relative to Lo. Force deficit was evaluated 10 min after the 75 contractions and then the incision was closed with 7-0 silk suture. Animals were returned to their cage to recover until the time of sacrifice. Prior to sacrifice by cervical dislocation, animals were anesthetized with avertin and the EDL muscles were excised and flash frozen in liquid nitrogen. Muscles were stored in liquid nitrogen until RNA isolation. RNA Isolation. Total RNA was isolated from EDL muscles from control mice (n=3) and mice sacrificed at 6 h (n=3) and 72 h (n=3) after lengthening contractions according to the modified protocol of Chomzynski et al.. Frozen muscles were added to preweighed tubes containing TriReagent (Sigma-Aldrich, St. Louis, MO). Tissue was homogenized in TriReagent using a Tissue Tearor (Fischer, Pittsburgh, PA) at 30,000 rpm for 1 minute. Homogenates were transferred to sterile, RNAase free microcentrifuge tubes and incubated for 10 min at room temperature. Chloroform (0.2 ml; Sigma-Aldrich, St. Louis, MO) was added and after incubation, the samples were centrifuged for 15 min at 12,000 g and 4Â°C. Total RNA was precipitated from the aqueous phase by the addition of isopropanol (Sigma-Aldrich), and pelleted by centrifugation. Pellets were washed in ethanol (75 and 95 %) and air dried before resuspension in diethylpyrocarbonate (DEPC) treated water. RNA concentration was determined by optical density at 260 nm. III. Hybridization procedures and parameters: Microarray Hybridization and Analysis. To reduce measurement error, all membranes (Atlas mouse 1.2; Clontech, Palo Alto, CA) were prepared from the same lot. Additionally, each membrane was hybridized only once to avoid errors associated with stripping and multiple hybridizations. In order to minimize individual biological variability, total RNA was pooled from three animals for hybridization of arrays. Three arrays were used for the pooled sample at each time point. First strand cDNA probe generation from total RNA and microarray hybridization were performed according to manufacturerâs instructions (Atlas cDNA Expression Arrays User Manual, Clontech). 33P labeled cDNA was generated from sample RNA using [33P]-dATP (3000 Ci/mmol; ICN, Costa Mesa, CA) and Maloney murine leukemia virus (MMLV) reverse transcriptase (Clontech). Labeled probes were purified using nucleospin columns (Clontech). Array membranes were prehybridized in Express Hyb containing sheared Salmon testes DNA (Gibco BRL, Rockville, MD) for 30 min at 71Â°C in rotating hybridization tubes. Radiolabeled probe (3 x 106 cpm) was incubated in denaturing solution (Clontech) for 20 min at 71Â°C, after which Cot1 DNA/neutralizing solution was added and incubation continued for 10 min. The probe mixture was added to the hybridization tube and incubated with rotation overnight. Following hybridization, membranes were washed four times for 30 min in 2X saturated sodium citrate (SSC) and 1 % sodium dodecyl sulphate (SDS) at 71Â°C, once for 30 min in 0.1X SSC and 0.5% SDS at 71Â°C, and once for 5 min in 2X SSC at room temperature. Membranes were removed and immediately wrapped in plastic and exposed to a phosphor storage screen (Molecular Dynamics, Sunnyvale, CA) for four days. IV. Measurement data and specifications: Data Analysis. The membrane image was acquired using a Storm phosporimager (Molecular Dynamics) and Image Quant software. Array images were analyzed using Atlas Image 2.0 (Clontech) software to determine raw intensity levels of expression. Raw intensity data was imported into GeneSpring (Silicon Genetics, Redwood City, CA) expression analysis software. Intensity levels were normalized to the median expressed intensity on each of the arrays and averaged for the three arrays at each time point. Normalized expression levels for control arrays were established as a value of 1 and data from 6 and 72 h were expressed as fold changes relative to control. In order to simplify interpretation of the resulting dataset, a k-means cluster analysis was employed to group genes based on similarities in patterns of expression. To reduce the likelihood of false positives, the data was filtered using a criterion 2 fold change in expression prior to clustering. Miller et al. (61) have calculated that using an array of 10,000 features with a coefficient of variation (CV) of 20 percent, a 2 fold criterion for altered gene expression would result in zero false positives. The mean and median CV (15.8 and 14.3%, respectively) for all arrays in the current study fell within these guidelines for the elimination of false positives.

Project description:Duchenne muscular dystrophy is due to genetic abnormalities in the dystrophin gene and represents one of the most frequent genetic childhood diseases. In the X-linked muscular dystrophy (mdx) mouse model of dystrophinopathy, different subtypes of skeletal muscles are affected to a varying degree albeit the same single base substitution within exon 23 of the dystrophin gene. Thus, to determine potential muscle subtype-specific differences in secondary alterations due to a deficiency in dystrophin, in this study, we carried out a comparative histological and proteomic survey of mdx muscles. We intentionally included the skeletal muscles that are often used for studying the pathomechanism of muscular dystrophy. Histological examinations revealed a significantly higher degree of central nucleation in the soleus and extensor digitorum longus muscles compared with the flexor digitorum brevis and interosseus muscles. Muscular hypertrophy of 20-25% was likewise only observed in the soleus and extensor digitorum longus muscles from mdx mice, but not in the flexor digitorum brevis and interosseus muscles. For proteomic analysis, muscle protein extracts were separated by fluorescence two-dimensional (2D) gel electrophoresis. Proteins with a significant change in their expression were identified by mass spectrometry. Proteomic profiling established an altered abundance of 24, 17, 19 and 5 protein species in the dystrophin-deficient soleus, extensor digitorum longus, flexor digitorum brevis and interosseus muscle, respectively. The key proteomic findings were verified by immunoblot analysis. The identified proteins are involved in the contraction-relaxation cycle, metabolite transport, muscle metabolism and the cellular stress response. Thus, histological and proteomic profiling of muscle subtypes from mdx mice indicated that distinct skeletal muscles are differentially affected by the loss of the membrane cytoskeletal protein, dystrophin. Varying degrees of perturbed protein expression patterns in the muscle subtypes from mdx mice may be due to dissimilar downstream events, including differences in muscle structure or compensatory mechanisms that counteract pathophysiological processes. The interosseus muscle from mdx mice possibly represents a naturally protected phenotype.

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Dataset Information

Differential effects of acute changes in cell Ca2+ concentration on myofibrillar and non-myofibrillar protein breakdown in the rat extensor digitorum longus muscle in vitro. Assessment by production of tyrosine and N tau-methylhistidine.

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