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Biomedical subjects

K Wildenthal

Publications and source records attributed to K Wildenthal.

At least 19 recordsLinked to original sources
PubMed1986

Disproportionate reduction of actin synthesis in hearts of starved rats.

We examined the synthesis of proteins in rat myocardium after starvation. Rates of total protein synthesis in myofibrillar and nonmyofibrillar fractions of myocardium of starved animals were reduced similarly (to 70-80% of the rates in hearts of fed animals, p less than 0.002), but rates of synthesis of some individual proteins were affected discoordinately. Radiolabeled proteins from atrial and ventricular explants, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, revealed that starvation for 2 days reduced the rate of cardiac actin synthesis to 26-38% of control levels, while the rate of myosin heavy chain synthesis in the same hearts was only moderately reduced (74-80% of control levels). This starvation-induced reduction in actin synthesis could be accounted for at least in part by disproportionately decreased levels of actin mRNA in starved hearts, as revealed by Northern blot hybridization and by in vitro translation analysis. The dramatic decrease in cardiac actin synthesis was rapidly reversible, and actin synthesis returned to normal after a single day of refeeding. The selective reduction of actin synthesis after starvation was specific for the heart: rates of myosin heavy chain and actin synthesis in skeletal muscles (soleus and extensor digitorum longus) were coordinately reduced in response to starvation. To our knowledge, this is the first example of such dramatic discoordinate regulation of myofibrillar protein synthesis in response to a physiological stimulus.

Actins↗
PubMed1986

Lysosomal responses of fetal mouse hearts recovering from anoxia and substrate depletion.

Recovery from a 1 h period of anoxia and substrate deprivation is accompanied by a marked lysosomal response in myocytes of fetal mouse hearts maintained in organ culture. Two classes of subcellular vacuoles form within 5 to 15 min of recovery. One appears to provide lysosomal enzymes for degradation of subcellular particles, while the other segregates organelles within the cytoplasm of the injured myocyte. When the two populations fuse with each other, the degradation of sequestered organelles appears to commence. After 6 h of recovery, intravacuolar degradation appears complete, and the injured myocytes are morphologically indistinguishable from control cells, demonstrating that the breakdown of the partitioned cell organelles is quite efficient. The process can proceed, albeit at a reduced rate, while protein synthesis is inhibited, since cycloheximide only modestly interferes with recovery after reoxygenation. The present results demonstrate that the fetal mouse heart subjected to conditions that simulate some important aspects of ischemia is an excellent model to examine the role of lysosomes during recovery from sublethal injury.

Animals↗
PubMed1986

Influence of agents that alter lysosomal function on fetal mouse hearts recovering from anoxia and substrate depletion.

Recovery of fetal mouse heart myocytes from oxygen and substrate deprivation for 1 h is accompanied by complicated lysosomal and non-lysosomal vacuolar responses which can be subdivided temporally into four distinct phases that include production of lysosomal dense bodies; segregation of damaged subcellular organelles into vacuoles that initially lack lysosomal enzymes; delivery of lysosomal enzymes to these vacuoles through fusion with dense bodies, transforming them into lysosomal autophagic vacuoles and degradation of the sequestered organelles. These events are normally completed within 6 h of the resupply of oxygen and substrate. The progression of these events is influenced significantly by pharmacological interventions that alter lysosomal properties. Chloroquine inhibits all aspects of the lysosomally-related processes as well as the sequestration phase during recovery. Leupeptin delays the lysosomal degradation, presumably by slowing proteolysis. Hydrocortisone permits the engulfment phase and the appearance of lysosomal dense bodies but appears to prevent or postpone the delivery of lysosomal enzymes to many of the large vacuoles and to delay the degradation of sequestered organelles. These observations reveal that segregation of damaged organelles and lysosomally-mediated degradation of these subcellular structures are important events during recovery from ischemic-like injury, and that agents that interfere with normal lysosomal function can prevent or delay some or all of the lysosomal responses that are involved in the recovery process.

Animals↗
PubMed1986

Effects of glucocorticoid treatment on cardiac protein synthesis and degradation.

We treated rats with dexamethasone (DEX, 1 mg . kg-1 . day-1) and examined the effects of this glucocorticoid on heart protein metabolism using atrial explant and Langendorff perfusion preparations. Fasted rats treated with DEX for 2 days had significantly lower body weights (92% of control, P less than 0.001) and larger hearts (106% of control, P less than 0.005) than fasted control animals. Protein and RNA concentrations remained constant. In atrial explants, DEX treatment produced a 19% increase in protein synthesis (P less than 0.001) and a 13% increase in protein degradation (P less than 0.002). In Langendorff-perfused hearts, DEX treatment caused a 36% increase in protein synthesis (P less than 0.02), while protein degradation was 8% above control (P greater than 0.05). Thus, in contrast to their catabolic effects on skeletal muscle, glucocorticoids are anabolic on the heart. The increased accumulation of total cardiac protein during early glucocorticoid administration is mediated entirely via increased rates of synthesis.

Animals↗
PubMed1985

The role of lysosomes and microtubules in cardiac protein degradation.

The mechanisms and regulatory factors involved in cardiac proteolysis are incompletely understood. Agents that interfere with lysosomal function (e.g., chloroquine, leupeptin, methyladenine) cause a 25-30% reduction in the overall rate of protein degradation. In the same hearts, however, the rate of myosin breakdown remains unchanged. Disaggregation of micro-tubules with colchicine is accompanied by a 15% reduction in the rate of degradation of total protein and of myosin. In the same hearts, the degradation of "organellar" protein, including mitochondrial cytochromes, is reduced by over 30%. Thus, it appears that the degradation of different classes of cardiac proteins may be accomplished and regulated by different processes. Lysosomes are important in overall proteolysis, but appear not to be involved in the regulation of myosin breakdown. Microtubules are also involved in the proteolytic process, and appear to be especially important for the breakdown of proteins from mitochondria and perhaps other organelles.

Animals↗
PubMed1985

The role of lysosomes in the degradation of myofibrillar and non-myofibrillar proteins in heart.

Lysosomes are presumed to be involved in protein degradation in heart, but their exact role is poorly understood. Several interventions that are known to alter cardiac proteolysis (e.g., insulin) also produce lysosomal changes that might account for the observed changes in protein degradation; but many other interventions appear not to do so. Agents that interfere with lysosomal function (e.g., sucrose, chloroquine, methyladenine, leupeptin) cause a 25% reduction in the rate of degradation of total protein in fetal mouse hearts in organ culture; however, in the same hearts the rate of degradation of myosin and other myofibrillar proteins remains unchanged. Thus, it appears that lysosomes are involved in cardiac proteolysis, but may not play a rate-limiting or regulatory role in many circumstances. The regulation of proteolysis by insulin appears to involve non-lysosomal pathways in addition to any lysosomal alterations it may cause. Furthermore, the initial cleavage of myofibrillar proteins appears no to be dependent on normal lysosomal function.

Adenine↗
PubMed1979

Influence of a phosphodiesterase inhibitor on the chronotropic effects of glucagon and norepinephrine in fetal mouse hearts.

Fetal mouse hearts develop tachycardia in response both to norepinephrine and to glucagon, but although adenylate cyclase is stimulated and adenosine 3':5'-monophosphate (cyclic AMP) elevated by norepinephrine, no measurable changes are produced by glucagon. To test further the possible independence of glucagon chronotropy from the cyclic AMP system, the effects of a phosphodiesterase inhibitor were evaluated. The dose-response curve to norepinephrine was shifted to the left by the phosphodiesterase inhibitor 4-(3,4-dimethoxybenzyl)-2-imidazolidinone (Ro7-2956), but the dose-response curve to glucagon was unaltered. Thus, 10(-6) M norepinephrine produced an increase of 40 +/- 5 beats/min in hearts pretreated with Ro7-2956, as compared to an increase of 22 +/- 3 in control hearts (P less than .01). In contrast, 10(-6) M glucagon produced a rate increase of 25 +/- 4 beats/min in treated hearts vs. 26 +/- 4 beats/min in controls. These data are compatible with the hypothesis that adenylate cyclase and cyclic AMP are involved in the chronotropic response of the fetal mouse heart to norepinephrine but not to glucagon.

Animals↗
PubMed1978

Regulation of cardiac protein balance by hydrocortisone: interaction with insulin.

In fetal mouse hearts in organ culture the rate of protein synthesis was substantially reduced and the rate of protein degradation slightly increased by hydrocortisone in the absence of insulin, but in the presence of insulin the steroid caused a small increase in protein synthesis and a significant reduction in protein degradation. Hydrocortisone promoted the net uptake (or reduced the net release) of branched-chain amino acids independent of insulin and independent of simultaneous changes in protein balance. The specific activities of the lysosomal enzymes cathepsin D and glucosaminidase were reduced by hydrocortisone in all media, whereas the specific activity of creatine kinase increased when the medium contained insulin but decreased in the absence of insulin. It is concluded that hydrocortisone regulates cardiac protein balance via alterations both in synthesis and in degradation. Some of the hormone's myocardial effects are influenced by insulin so that hydrocortisone is anabolic in its presence but catabolic in its absence.

Amino Acids↗
PubMed1978

Species differences in responses to hyperosmolality and D600 in cat and rat heart.

The direct inotropic effect of hypertonic mannitol was compared in isolated rat and cat papillary muscles. The inotropic effects of paired electrical stimulation and D600 were also evaluated in the same species. At extracellular calcium concentrations of 2.5 mM, hypertonic mannitol (25--100 mosmol/kg H2O above normal) depressed contractility in isolated rat myocardium; hyperosmolality exerted a positive effect only when extracellular Ca2+ was low (e.g., 0.3 mM). Paired pacing exerted a small but significant inotropic effect in rat heart when extracellular Ca2+ was 2.5 mM, and a larger effect at lower Ca2+. As previously noted, hypertonic mannitol and paired pacing both produced significant positive effects in isolated cat heart at an extracellular Ca2+ concentration of 2.5 mM. D600 exerted less of a depressant effect on contractility in rat than in cat heart at concentrations of 10(-6)--10(-7) M. The data suggest that 1) in contrast to results in cat heart, the positive inotropic effect of hyperosmolality in isolated rat cardiac muscle is apparent only when extracellular calcium concentration is reduced; 2) the inotropic effect of paired pacing in rat heart is greatest at low Ca2+ levels, but persists to a lesser degree at extracellular calcium concentrations of 2.5 mM; and 3) D600-inhibitable calcium channels appear to be relatively less important in the maintenance of cardiac contractility in rat than in cat cardiac muscle.

Animals↗
PubMed1978

Inhibition of protein degradation in mouse hearts by agents that cause lysosomal dysfunction.

Although the heart contains lysosomes, it has been uncertain whether these organelles and their proteolytic enzymes can play an important role in cardiac protein degradation. Recent studies have demonstrated that fetal mouse hearts in organ culture sustain selective derangements in lysosomal structure and function during exposure to chloroquine or nonmetabolizable sugars. Accordingly, we tested the effects of these agents on cardiac proteolysis under controlled conditions in vitro using two techniques (measurement of loss of radioactivity from trichoroacetic acid-precipitable protein after prelabeling with tritiated phenylalanine and measurement of loss of cold phenylalanine after blockade of protein synthesis with cycloheximide). Chloroquine (0.1 mM) reduced the average rate of protein breakdown in hearts of matched littermates from 45%/24 hours to 32%/24 hours (P less than 0.01) and decreased the release of cold phenylalanine by 31 +/- 5% (0.108 vs 0.075 nmol/mg per hour, P less than 0.01). Exposure to 100 mM sucrose for 24-48 hours reduced the rate of breakdown from 44%/24 hours to 33%/24 hours (P less than 0.01) and decreased the release of cold phenylalanine by 35 +/- 9% (0.092 vs. 0.060 nmol/mg per hour, P less than 0.01). The results suggest that interference with lysosomal function in cultured fetal mouse hearts causes a significant reduction in the cardiac capacity to degrade proteins.

Amino Acids↗
PubMed1978

Synthesis and degradation of myocardial protein during the development and regression of thyroxine-induced cardiac hypertrophy in rats.

Cardiac hypertrophy was induced in rats by daily injections of L-thyroxine (1.0 mg/kg). Regression from hypertrophy was studied 4 days after discontinuing thyroxine. Isolated, Langendorff-perfused hearts were perfused with Krebs-Henseleit buffer, glucose, insulin, and amino acids. To measure protein synthesis, left ventricular tissue was assayed for incorporation of tritiated phenylalanine into protein. Indices of rates of protein degradation were obtained by measuring the release of cold phenylalanine after blocking protein synthesis with cycloheximide. After 3 days of thyroxine (when cardiac growth was maximally increased), the rate of protein synthesis increased by 22% (P less than 0.001). After 1 week, synthesis was 8% greater than control (P less than 0.05), and by 2 weeks (when hypertrophy was stable and the rate of cardiac growth was similar to controls), synthesis had returned to control levels. In hearts regressing from hypertrophy, synthesis was reduced to 68% of control (P less than 0.001). The rate of protein degradation was decreased by 12% (P less than 0.05) after 3 days of thyroxine, but was not different from control at 1 or 2 weeks. During regression, degradation was 12% below control (P less than 0.05). Changes in the release of several amino acids that are synthesized or metabolized in heart (e.g., alanine, glycine, serine) were different from changes in phenylalanine release. In conclusion thyroxine-induced cardiac hypertrophy and regression are accompanied by changes in protein synthesis and degradation, and amino acid metabolism. The predominant change in hypertrophy is increased protein synthesis with a minor contribution from reduced degradation. Regression of hypertrophy is accompanied by decreased synthesis, not increased degradation.

Amino Acids↗