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Myocardial mRNA content and stability, and enzyme activities of Ca-cycling and aerobic metabolism in canine dilated cardiomyopathies (1995)

O'Brien, Peter James ; Duke, Angie L. ; Shen, Hua ; [et al.]

Springer

Molecular and cellular biochemistry 142 (1995), S. 139-150

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ISSN: 1573-4919

Keywords: canine idiopathic dilated cardiomyopathy ; calcium release channel ; mRNA ; oxidative phosphorylation ; myoglobin

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Abstract Idiopathic dilated cardiomyopathy is associated with derangement of myocardial sarcoplasmic Ca-homeostasis and energy production. The molecular mechanism for these changes is unknown. Accordingly, we used genetic and experimentally-induced models of canine dilated cardiomyopathy and tested the hypothesis that these metabolic changes resulted from altered gene expression, as indicated by mRNA content. We studied dilated cardiomyopathy occurring naturally (n=9) in Doberman pinschers, and in dogs subjected to rapid ventricular pacing (n=5), in comparison with normal dogs (n=9). We determined content and integrity of mRNA's using Northern and slot blotting, and measured activities of their translated product for the Ca-release channel and Ca-ATPase of sarcoplasmic reticulum, lactate dehydrogenase of glycolysis, citrate synthase of the tricarboxylic acid cycle, and for myoglobin, ATP-synthetase and the adenine nucleotide transporter, which are integral in oxidative phosphorylation. We found that, whereas both mRNA content and enzyme activity for markers of Ca-cycling, glycolysis, and oxidative phosphorylation were downregulated (20–80%) in dilated cardiomyopathy, they were upregulated (10–15%) for tricarboxylic acid cycling and for ribosomal RNA. RNA from cardiomyopathic tissue was up to 50% more degraded than for normal hearts in association with a 150% increase in ribonuclease activity. Downregulation of the Ca-cycle was asymmetric, with the Ca-channel being 65% more affected than the Ca-ATPase. This work supports the general paradigm that transcriptional and translational responses to pathophysiology are major determinants of the metabolic response seen in cardiac failure.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00928935

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Effects of hypocaloric feeding and refeeding on myocardial Ca and ATP cycling in the rat (1995)

O'Brien, Peter James ; Shen, Hua ; Bissonette, David ; [et al.]

Springer

Molecular and cellular biochemistry 142 (1995), S. 151-161

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ISSN: 1573-4919

Keywords: hypocaloric feeding ; rat ; myocardium ; sarcoplasmic reticulum ; Ca-release channel ; Ca-ATPase

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Abstract Hypocaloric feeding (HCF) depresses heart function causing cardiac atrophy, bradycardia, and decreased cardiac output. We tested the hypothesis that HCF results in decreased myocardial Ca- and ATP cycling. We reduced protein-calorie intake of adult rats by 20% for 7 days and then allowed them to recover for 3 days. Changes in ionized Ca concentration (nM/s) of 2.5% myocardial homogenates that were attributable to the Ca-ATPase pump and Ca-release channel (CRC), respectively, of the sarcoplasmic reticulum (SR) were depressed 41 and 85% by HCF from 61.6±9.4 and 24.7±3.3, to 36.1±2.8 and 3.6±2.9. Activity of the Ca-pump was restored after 3 days of refeeding, whereas the CRC remained 23% depressed (all p〈0.05). Additionally, the CRC activity was inhibited to a 3-fold greater extent than controls by HCF, but was disinhibited within one day of refeeding. The greater effect on CRC than Ca-pump activity resulted in net Ca-uptake being unaffected by HCF. In addition to depression of Ca-cycling, ATP sythetase and total ATPase activities (IU/g), respectively, were depressed 20 and 15% by HCF from 174±19 and 51.3±3.8 to 140±15 and 43.7±4.7, but were restored to control values within one day of refeeding. We conclude that HCF produces a compensatory, reversible, and asymmetric downregulation and inhibition of Ca-cycling, with the CRC being preferentially affected.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00928936

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Myocardial Ca-sequestration failure and compensatory increase in Ca-ATPase with congestive cardiomyopathy: kinetic characterization by a homogenate microassay using real-time ratiometric indo-1 spectrofluorometry (1991)

O'Brien, Peter James ; Shen, Hua ; Weiler, Janice ; [et al.]

Springer

Molecular and cellular biochemistry 102 (1991), S. 1-12

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ISSN: 1573-4919

Keywords: sarcoplasmic reticulum ; calcium-sequestration ; furazolidone cardiomyopathy ; indo-1 ; spectrofluorometry

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Abstract A novel, simple, rapid and reproducible microassay is used for kinetic analysis of Ca-sequestration by homogenates of myocardium of turkeys with furazolidone-induced congestive cardiomyopathy. The assay monitors Ca in real-time using dual-emission ratiometric spectrofluorometry and the Ca-indicator dye indo-1. Using this assay and isolated SR studies we make several novel findings regarding the mechanism of SR failure in furazolidone cardiomyopathy. Qualitative differences in Ca-sequestration were not detected between groups. However, compared to controls the furazolidone treatment resulted in: 1) 50% depression in maximal activities (1.54 ± 0.36 vs 0.73 ± 0.12 µM/sec); 2) 2-fold increases in post-sequestration concentrations of ionized Ca(79 ± 23 vs 141 ±13 nmol Ca/L homogenate); 3) 2-fold increases in Ca half-life (415 vs 790 msec); and 4) 25% increased passive Ca-binding capacity of homogenates. The Ca-ATPase specific activity of isolated sarcoplasmic reticulum was 60% increased in congestive cardiomyopathy (543 ± 140 vs 873 ± 108 nmol ATP hydrolyzed/min/mg membrane protein) although membrane yield was 20% decreased (0.79 ± 0.09 vs 0.63 ± 0.03 mg/g heart). The increased ATPase and decreased Ca-uptake activities in combination with the occurrence of 36% cardiac hypertrophy and 19% decreased body weights resulted in estimates of the relative energy cost to the animal for myocardial Ca transport being 5.5-fold increased with cardiomyopathy (20.5 vs 111 nmol ATP hydrolyzed per µM decrease of sarcoplasmic free Ca/kg body weight). These data indicate that congestive cardiomyopathy is associated with markedly increased permeability of sarcoplasmic reticulum to Ca and compensatorily increased Ca-ATPase activity. Accelerated energy consumption due to the increased energy cost of Ca transport and increased time of myocyte activation are predicted to predispose the myocardium to fatigue and irreversible failure.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00232153

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Rapid, simple and sensitive microassay for skeletal and cardiac muscle myoglobin and hemoglobin: use in various animals indicates functional role of myohemoproteins (1992)

O'Brien, Peter James ; Shen, Hua ; McCutcheon, Laura Jill ; [et al.]

Springer

Molecular and cellular biochemistry 112 (1992), S. 45-52

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ISSN: 1573-4919

Keywords: myoglobin ; hemoglobin ; muscle ; heart ; microassay ; mammals ; birds ; fish

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Abstract A novel, simple, rapid, sensitive and reproducible microassay is described for determination of myoglobin and hemoglobin content of myocardial and skeletal muscle biopsy specimens from various mammals, birds and fish. As little as 50 mg of tissue is needed and myoglobin concentrations lower than 1 mg% can be detected. Myoglobin and hemoglobin are separated at alkaline pH by ammonium sulfate extraction followed by ultrafiltration. Heme content is determined by absorption of the Soret band when the hemoprotein extract is visibly colored or more sensitively by its peroxidase activity when the extract has low color. The heme reacts with tertiary-butyl hydroperoxide and orthotolidine to generate a blue color. Hemoglobin content is correlated with myoglobin content and is related to aerobic capacity and blood flow to the tissue. Myoglobin content varied over 5 orders of magnitude up to 7 per cent of the weight of tissue, whereas hemoglobin content varied over 2 orders of magnitude up to 6 per cent of tissue weight. Myoglobin content is increased in species with high basal metabolic rate, high physical activity, prolonged diving capacity, fatigue resistance, and red muscle, whereas it is decreased in white muscle, iron-deficient animals, animals with sedentary lifestyles, and in animals and tissues with small fiber diameters such as avian or fish hearts.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00229642

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