scholarly journals Contrasting response of protein degradation to starvation and insulin as measured by release of Nτ-methylhistidine or phenylalanine from the perfused rat heart

1986 ◽  
Vol 237 (2) ◽  
pp. 391-395 ◽  
Author(s):  
D M Smith ◽  
P H Sugden
Keyword(s):  
Protein Degradation ◽  
Rat Heart ◽  
Isotope Dilution Method ◽  
Dilution Method ◽  
Intracellular Protein ◽  
Perfused Rat Heart ◽  
Fractional Rate ◽  
Degradation Rates ◽  
Actin Degradation ◽  
Mixed Protein

An isotope-dilution method is described for the measurement of N tau-methylhistidine release from the perfused rat heart. We argue that release of N tau-methylhistidine is indicative of cardiac actin degradation. N tau-Methylhistidine release is compared with phenylalanine release in the presence of cycloheximide (phenylalanine release being a measure of degradation of mixed proteins). In hearts perfused with glucose plus acetate, the rate of actin degradation was increased by starvation and was not inhibited by insulin. In contrast, the rate of mixed-protein degradation was decreased by starvation and was inhibited by insulin. The fractional rate of degradation of mixed proteins in hearts from fed or starved rats was greater than that for actin. It is suggested that there are at least two pools of intracellular protein, the degradation rates of which differ in terms of their response to insulin and starvation.

scholarly journals The effects of glucose, acetate, lactate and insulin on protein degradation in the perfused rat heart

1982 ◽  
Vol 206 (3) ◽  
pp. 467-472 ◽  
Author(s):  
P H Sugden ◽  
D M Smith
Keyword(s):  
Protein Degradation ◽  
Rat Heart ◽  
Plasma Concentrations ◽  
Normal Range ◽  
Perfused Rat Heart ◽  
Rat Hearts ◽  
Insulin Inhibition

Rat hearts were perfused as working preparations by the method of Taegtmeyer, Hems & Krebs [(1980 Biochem. J. 186, 701-711]. In the presence of glucose, insulin significantly inhibited protein degradation at concentrations as low as 50 mu units/ml. Acetate or lactate, when present either as sole fuel for contraction or in combination with glucose, did not inhibit protein degradation. Insulin inhibition or protein degradation was decreased with either lactate as sole fuel. We suggest that the inhibition of protein degradation occurs over the normal range of plasma concentrations of insulin present in vivo and that the presence of glucose may be at least in part necessary for this effect of insulin.

Proteolysis in cultured cells during prolonged serum deprivation and replacement

1986 ◽  
Vol 251 (5) ◽  
pp. C748-C753 ◽  
Author(s):  
J. J. Berger ◽  
J. F. Dice
Keyword(s):  
Protein Degradation ◽  
Cultured Cells ◽  
Cellular Level ◽  
Serum Deprivation ◽  
Intracellular Protein ◽  
Physiological Importance ◽  
Human Diploid Fibroblasts ◽  
Degradation Rates ◽  
Intracellular Protein Degradation

Cells in culture show a series of changes in intracellular protein degradation in response to serum deprivation and replacement that are similar to alterations in degradation in tissues of starved and refed animals. Rates of intracellular protein degradation are increased in confluent cultures of IMR-90 human diploid fibroblasts when deprived of serum, but this enhanced proteolysis is transient. By 24-48 h, rates of protein degradation decline to values comparable to or below those for cells incubated in the presence of serum. Longer serum deprivation leads to further reductions in proteolysis. The reduced proteolysis after long-term deprivation cannot be explained by experimental artifacts or by gradual depletion of glucocorticoids or thyroid hormones from cells. Readdition of serum to deprived cells that are still in the enhanced phase of proteolysis restores degradation rates to values comparable to those in nondeprived cells. However, in cells deprived of serum for 24-48 h or longer, readdition of serum to the medium results in a marked reduction in proteolysis to rates below those observed in nondeprived cells. These responses of cultured cells to long-term serum deprivation and readdition may be of considerable physiological importance in that the proteolytic responses of tissues in starved and refed animals may be at least partially due to mechanisms operating at the cellular level.

Effect of redox potential on protein degradation in perfused rat heart

1985 ◽  
Vol 248 (6) ◽  
pp. E726-E731
Author(s):  
B. H. Chua ◽  
B. J. Kleinhans
Keyword(s):  
Energy Source ◽  
Redox Potential ◽  
Protein Degradation ◽  
Rat Heart ◽  
Redox State ◽  
Inhibitory Effect ◽  
Experimental Conditions ◽  
Perfused Rat Heart ◽  
Rat Hearts ◽  
Sole Energy

The effect of redox potential on protein degradation was assessed in rat hearts supplied either glucose or pyruvate, and the correlation between redox state and proteolysis was examined after the addition of insulin and leucine. In hearts supplied glucose as the sole energy source, the inhibition of protein degradation by a range of concentrations of insulin was associated with increased ratios of perfusate lactate to pyruvate and intracellular lactate to pyruvate, malate to pyruvate, and NADH to NAD. However, the extent of inhibition did not correlate with the redox state. The inhibitory effect of leucine on protein degradation was not accompanied by any change in redox state of the hearts. In hearts provided with pyruvate, rates of protein degradation continued to be inhibited by insulin even though the perfusate lactate to pyruvate was decreased by 14-fold and the calculated cytosolic NADH-to-NAD ratios were only 3% of those seen in hearts supplied glucose. These results indicated that a correlation between redox state and protein degradation was not apparent in myocardium under the experimental conditions examined.

scholarly journals Distinction between major chloroquine-inhibitable and adrenergic-responsive pathways of protein degradation and their relation to tissue ATP content in the Langendorff isolated perfused rat heart

1988 ◽  
Vol 251 (2) ◽  
pp. 341-346 ◽  
Author(s):  
T D Lockwood
Keyword(s):  
Protein Degradation ◽  
Rat Heart ◽  
Degradation Rate ◽  
Contractile Function ◽  
Left Ventricular ◽  
Atp Content ◽  
Perfused Rat Heart ◽  
Isolated Perfused Rat Heart ◽  
Ventricular Tissue ◽  
Lysosomal Protein

In the Langendorff isolated perfused rat heart, 36% of total basal protein degradation was inhibited by the lysosomal inhibitor chloroquine (30 microM), after elimination of rapid turnover proteins during a 3 h preliminary degradation period. Prior inhibition of degradation with chloroquine was additive to the 30% inhibition caused by simultaneous infusion of 50-200 nM-isoprenaline. This additivity suggests that the adrenergic-controlled process is independent of the lysosomal degradative pathway. After discontinuation of drug infusions, the isoprenaline-inhibited degradation rate returned to the previous baseline; however, the chloroquine-inhibited degradation rate transiently exceeded the previous baseline. NaN3 (0.3 mM) caused a decrease of left-ventricular myocardial ATP content of approx. 60% at 14 min and extreme impairment of contractile function; however, the total lysosomal and non-lysosomal protein degradation was not changed at this time. Conversely, left-ventricular tissue ATP content was not changed during proteolytic inhibition by 10 nM-isoprenaline or 10 microM-chloroquine at 14 min. The results indicate that depletion of myocardial energy stores in this preparation is neither necessary nor sufficient to cause inhibition of the total of lysosomal and non-lysosomal protein degradation.

Protein synthesis rate is not suppressed in rat heart during senescence

1990 ◽  
Vol 258 (1) ◽  
pp. H207-H211 ◽  
Author(s):  
R. B. Biggs ◽  
F. W. Booth
Keyword(s):  
Protein Synthesis ◽  
Rat Heart ◽  
Age Groups ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Fischer 344 ◽  
Fractional Rate ◽  
Rat Hearts ◽  
Old Rats ◽  
Mixed Protein

The purpose of these experiments was to determine whether mixed protein synthesis rates in hearts of Fischer 344 rats were decreased from maturity to senescence. When compared with 12-mo-old rat hearts, hearts from 23- to 25-mo-old rats had 13% lower concentrations of noncollagen protein, 9% less non-collagen protein per heart, 10% higher ratio of heart wet weight-to-body weight, and no difference in the basal rate of mixed protein synthesis, when expressed as fractional rate per day. Despite the 9% decrease in total noncollagen protein in 23- to 25-mo-old rat hearts, the derived value for milligrams protein synthesized per day was not different between age groups. When triiodothyronine was given for 3 days to mature and senescent rats, fractional rates of mixed protein synthesis were increased by similar percents (57–70%) in hearts from these two age groups. Basal and triiodothyronine-stimulated RNA concentrations in hearts of 12-mo-old and 23- to 25-mo-old rats were not different. These observations showed no decrease in either the basal or the maximal thyroid-stimulated rates of mixed protein synthesis in the hearts between mature and senescent rats. Thus an aging-programmed downregulation of mixed protein synthesis rates within cardiac muscle did not occur in the senescent Fischer 344 rat heart in this study.

Sign in / Sign up

Export Citation Format

Share Document