Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.4.1 (myosin ATPase)
1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of diabetes on cardiac function was determined in isolated rat hearts. Diabetes was induced by injection of alloxan (doses ranged from 37.5 to 60 mg/kg body wt), and the heart were removed and perfused in the working heart preparation. Doses of alloxan ranging from 37.5 to 42 mg/kg did not consistently alter cardiac function even though serum glucose was elevated and serum thyroid hormones were reduced. Injection of 45 mg/kg of alloxan caused a large increase in serum glucose and a larger decrease in thyroid hormones. In this case, ventricular function was more consistently depressed after 1-2 wk. Function was not altered 48 h after injection of 60 mg kg of alloxan. However, when animals were given 60 mg/kg of alloxan and then maintained on insulin for 7 days, depressed cardiac function developed within 4 days after the insulin treatment was stopped. The decline in function involved a decrease in heart rate peak systolic pressure, and left ventricular +dP/dt. It was associated with greatly reduced serum thyroid hormones (both T3 and T4) and lower ventricular Ca2+-activated myosin ATPase activity. Fasting of rats for 4 days also resulted in decreased serum T3 and T4, depressed cardiac function (although heart rate was unchanged), and lower Ca2+-activated myosin ATPase activity.
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PMID:Decreased myocardial function and myosin ATPase in hearts from diabetic rats. 622 Jun 13

Previous studies have shown that in rats, diabetes mellitus induces a 45% decrease in cardiac Ca++-activated myosin ATPase activity which is accompanied by a decrease in myosin isoenzyme V1 and an increase in myosin isoenzyme V3 levels. Insulin administration reverts Ca++-activated myosin ATPase activity and myosin isoenzyme distribution to normal levels. It is currently unclear whether the effects of insulin on Ca++-myosin ATPase activity and myosin isoenzyme distribution are direct effects of the hormone or are mediated through insulin-induced alterations in cardiac metabolism. To determine if insulin may exert part of its effects by the latter route, diabetic rats were fed a normal, glucose, or fructose diet. Unlike glucose, fructose can enter the initial steps of the glycolytic pathway in the absence of insulin. Placing diabetic rats on different forms of 60% fructose diets for 4 weeks led to a 20-35% increase in Ca++-activated myosin ATPase activity, which was highly significant (normal Ca++-activated myosin ATPase activity, 0.917 mumol Pi/mg protein X min; diabetic, 0.553 mumol Pi/mg protein X min; diabetic + fructose, 0.661 mumol Pi/mg protein X min). The increase in Ca++-activated myosin ATPase activity was accompanied by increased myosin isoenzyme V1 and decreased myosin isoenzyme V3 levels. Feeding animals a 60% glucose diet did not lead to changes in Ca++-activated myosin ATPase activity or myosin isoenzyme distribution. The fructose-induced increase in Ca++-activated myosin ATPase activity and alteration in myosin isoenzyme distribution occurred in the absence of changes in insulin and thyroid hormone levels or improvement in the general metabolic status of fructose-fed diabetic rats.
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PMID:Fructose feeding increases Ca++-activated myosin ATPase activity and changes myosin isoenzyme distribution in the diabetic rat heart. 623 27

In order to determine whether diabetic cardiomyopathy in rats is associated with altered contractile proteins, male and female rats were made diabetic with intravenous streptozotocin (STZ). Calcium ATPase activity of cardiac actomyosin was significantly decreased after 1 week of diabetes and was depressed by 60% by 2 weeks. Rats pretreated with 3-O-methyl glucose to prevent the hyperglycemia caused by STZ had normal Ca2+-actomyosin ATPase activities, and non-diabetic rats whose food was restricted to keep their body and heart weights similar to those found in diabetic animals had only a slight fall in actomyosin ATPase activity. Ca2+-ATPase and actin-activated ATPase activities of pure myosin were similarly depressed in preparations from hearts of diabetic animals. Sodium dodecylsulfate gel electrophoresis and isoelectric focusing failed to reveal differences in the patterns of contractile proteins or light subunits between diabetics and controls, but pyrophosphate gels showed a shift in the myosin pattern. Because of depressed circulating thyroid hormone levels in diabetic animals, cardiac contractile proteins were also studied in preparations from thyroidectomized rats. Calcium activities of actomyosin and myosin ATPase were lower than values found in hearts of diabetic rats. When diabetic animals were kept euthyroid with thyroid replacement, actomyosin ATPase activity was still depressed. Thus STZ diabetes causes a significant decrease in cardiac contractile protein ATPase activity. This may be related to altered proportions of myosin isoenzymes.
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PMID:The effect of streptozotocin-induced diabetes in rats on cardiac contractile proteins. 645 19

Diabetes appears to cause a cardiomyopathy independent of atherosclerotic coronary artery disease and hypertension. Left ventricular papillary muscle function studies in rats made severely diabetic with streptozotocin have shown a slowing of relaxation and a depression of shortening velocity. However, the effects of insulin therapy on the myocardial mechanics of diabetic rats have not been studied. Therefore, rats diabetic for 6-10 weeks were treated with PZI insulin for 2, 6, 10, or 28 days and the mechanical performance of their left ventricular papillary muscles was compared to that of untreated diabetics and age-matched controls; cardiac contractile protein enzymatic activity was also measured. Neither 2 nor 6 days of therapy had any effects on the depressed cardiac muscle performance of diabetic animals, although plasma glucose concentration was restored to normal. By 10 days of therapy, recovery of mechanical performance was nearly complete, and by 28 days of therapy, complete reversal of the altered myocardial mechanics was observed. Crystalline insulin added to the bath (9 mU/ml) had no effect on myocardial mechanics in either diabetics or controls. A gradual recovery of actomyosin and myosin ATPase activity in the hearts of insulin-treated diabetic animals was also found, complementing the mechanical studies. In addition to demonstrating a gradual but complete reversibility of the abnormalities in papillary muscle function in diabetic rats (although control of hyperglycemia was less than ideal), this study confirms that this model of a cardiomyopathy is not a result of streptozotocin-induced cardiac toxicity. Additional data are provided indicating that depressed thyroid hormone levels in diabetic rats are not responsible for the mechanical changes observed.
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PMID:Reversibility of diabetic cardiomyopathy with insulin in rats. 703 May 13

The incidence of mortality from cardiovascular diseases in higher in diabetic patients. The cause of this accelerated cardiovascular disease is multifactorial and, although atherosclerotic cardiovascular disease in association with well-defined risk factors has an influence on morbidity and mortality in diabetics, myocardial cell dysfunction independent of vascular defects have also been defined. We postulate that these adverse cardiac effects could presumably result as a consequence of the following sequence of events. Major abnormalities in myocardial carbohydrate and lipid metabolism occur as a result of insulin deficiency. These changes are closely linked to the accumulation of various acylcarnitine and coenzyme derivatives. Abnormally high amounts of metabolic intermediates could cause disturbances in calcium homeostasis either directly or indirectly through structural and functional subcellular membrane alterations. Over time, chronic abnormalities such as reduced myosin ATPase activity, decreased ability of the sarcoplasmic reticulum to take up calcium as well as depression of other membrane enzymes such as Na(+)-K+ ATPase and Ca(2+)-ATPase leads to changes in calcium homeostasis and eventually to cardiac dysfunction. More importantly from the point of view of pharmacological intervention, during the initial stages, acute disturbances in both the glucose and FFA oxidative pathways may provide the initial biochemical lesion from which further events ensue. Thus therapies which target these metabolic aberrations in the heart during the early stages of diabetes, in effect, can potentially delay or impede the progression of more permanent sequelae which could ensue from otherwise uncontrolled derangements in cardiac metabolism. There is little dispute that an attempt should be made to lower raised plasma triglyceride and FFA levels. This would decrease the heart's reliance on fatty acids and, hence, overcome the fatty acid inhibition of myocardial glucose utilization. In this regard, the likely application of fatty acid oxidation inhibitors (CPT inhibitors, beta-oxidation inhibitors, sequestration of mitochondrial CoA) is also apparent.
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PMID:Myocardial substrate metabolism: implications for diabetic cardiomyopathy. 776 Mar 40

The size and quality of muscle specimens obtained by use of a percutaneous biopsy technique were studied. All biopsies were performed under local anesthesia, using an 11-gauge biopsy needle. The mean +/- SEM size of specimens obtained from 128 biopsies of the semitendinosus muscles of 16 Alaskan Huskies was 23.8 +/- 4.4 mg. All biopsy specimens were of sufficient quality to permit histochemical differentiation of the fiber types by use of myosin ATPase staining. An additional 8 biopsy specimens were obtained from 1 dog and analyzed for muscle glycogen content. These specimens contained 50.6 +/- 7.2 mmol of glucose/kg of muscle wet weight. This modified biopsy procedure was free of notable complications, and repeatable use produced specimens of adequate size and quality for histologic and biochemical analysis. It is concluded that this procedure is a safe and reliable alternative to open biopsy for diagnosis and management of neuromuscular, metabolic, and nutritional myopathies.
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PMID:New approach to percutaneous muscle biopsy in dogs. 853 88

Tight junctions serve as the rate-limiting barrier to passive movement of hydrophilic solutes across intestinal epithelia. After activation of Na+-glucose cotransport, the permeability of intestinal tight junctions is increased. Because previous analyses of this physiological tight junction regulation have been restricted to intact mucosae, dissection of the mechanisms underlying this process has been limited. To characterize this process, we have developed a reductionist model consisting of Caco-2 intestinal epithelial cells transfected with the intestinal Na+-glucose cotransporter, SGLT1. Monolayers of SGLT1 transfectants demonstrate physiological Na+-glucose cotransport. Activation of SGLT1 results in a 22 +/- 5% fall in transepithelial resistance (TER) (P < 0.001). Similarly, inactivation of SGLT1 by addition of phloridzin increases TER by 24 +/- 2% (P < 0.001). The increased tight junction permeability is size selective, with increased flux of small nutrient-sized molecules, e.g., mannitol, but not of larger molecules, e.g., inulin. SGLT1-dependent increases in tight junction permeability are inhibited by myosin light-chain kinase inhibitors (20 microM ML-7 or 40 microM ML-9), suggesting that myosin regulatory light-chain (MLC) phosphorylation is involved in tight junction regulation. Analysis of MLC phosphorylation showed a 2.08-fold increase after activation of SGLT1 (P < 0.01), which was inhibited by ML-9 (P < 0.01). Thus monolayers incubated with glucose and myosin light-chain kinase inhibitors are comparable to monolayers incubated with phloridzin. ML-9 also inhibits SGLT1-mediated tight junction regulation in small intestinal mucosa (P < 0.01). These data demonstrate that epithelial cells are the mediators of physiological tight junction regulation subsequent to SGLT1 activation. The intimate relationship between tight junction regulation and MLC phosphorylation suggests that a critical step in regulation of epithelial tight junction permeability may be myosin ATPase-mediated contraction of the perijunctional actomyosin ring and subsequent physical tension on the tight junction.
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PMID:Physiological regulation of epithelial tight junctions is associated with myosin light-chain phosphorylation. 935 84

The influence of glycation (non-enzymatic glycosylation) on structural and functional properties of actin of rabbit skeletal muscle and the effects of the natural anti-glycating dipeptide carnosine were studied. Glucose (0.5 M), fructose (0.5 M), and glyceraldehyde (0.05 M) were used as glycating agents. Marked changes in the structural and functional properties were observed in the presence of glyceraldehyde when high-molecular-weight components appear. This was followed by a decrease in the ability of actin to activate myosin ATPase, to polymerize, and to inhibit DNase I. In the presence of 0.05 M carnosine, the quantity of high-molecular-weight products decreased and myosin ATPase activation was retained. Since muscle tissue contains millimolar quantities of carnosine, glycation of actin associated with changes in its properties is evidently more likely to occur in non-muscle cells.
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PMID:Change in the functional properties of actin by its glycation in vitro. 946 33

Non-enzymatic glycosylation (glycation), a post-translational modification of proteins, results from the reaction of proteins with reducing sugars. Glycation is implicated in various pathologies like diabetes, Alzheimer's disease and it has been suggested to play an important role in the ageing process. Research on protein glycation has primarily studied extracellular proteins such as albumin, haemoglobin and collagen. However, there is increasing evidence that intracellular proteins may also be affected by glycation, and glycation of myosin is reported to decrease myosin ATPase activity. Glycated adducts are detected by various techniques such as chromatography, electrophoresis, fluorescence and immunochemistry. Inhibition or removal of these adducts has been achieved by chemical compounds such as aminoguanidine (amG), beta-mercaptoethanol (bME) and N-phenacylthiazolium bromide (PTB). In the present pilot study, using a novel in vitro motility assay, we have observed an attenuation in the motility speed of actin (approximately 13%) on myosin extracted from single muscle fibre segments after 15-min glucose incubation. Addition of bME to the incubation medium maintained actin motility speed.
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PMID:An overview of carbohydrate-protein interactions with specific reference to myosin and ageing. 1063 35

In this study we examined the effects of 3-24 h of incubation of chemically skinned rat fast-twitch muscle with the glycolytic metabolite glucose 6-phosphate (G6-P) on the contractile properties and myosin ATPase activity in single muscle fibres, and on the carbohydrate content of myosin heavy chains (MHCs). Exposure of the permeabilised muscle to 10 mM G6-P for 24 h at 22+/-1 degrees C in a rigor solution containing protease inhibitors and a reducing agent (dithiothreitol, DTT) significantly decreased maximum Ca(2+)-activated force output by 31%, lowered the Ca2+ threshold for contraction by 0.1 pCa units and produced shallower force-pCa curves compared with controls. Furthermore, under these conditions, G6-P-treated muscle displayed lower myofibrillar MgATPase activity and a markedly higher carbohydrate content of MHCs, as identified with an immunoblot protocol for glycoprotein detection. Shorter incubations under the same conditions or 24-h incubations with 5 mM G6-P generally resulted in smaller changes in the contractile activation parameters. These findings suggest that reducing sugars acting as metabolic intermediates in the glycolytic pathway can have important non-energy-related effects on the contractile activation characteristics of mammalian skeletal muscle. These effects are consistent with the glycation of muscle proteins, in particular that of the MHC.
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PMID:Ca2+-activation characteristics of single fibres from chemically skinned rat muscle incubated with glucose-6-phosphate. 1078 61


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