Turnover of muscle protein in the fowl. Changes in rates of protein synthesis and breakdown during hypertrophy of the anterior and posterior latissimus dorsi muscles

Measurements were made of the growth and of the changes in rates of protein turnover in the anterior latissimus dorsi muscle of the adult fowl in response to the attachment of a weight to one wing. Over 58 days there was a 140% increase in the protein content with similar increases in the RNA and DNA contents. The fractional rate of protein synthesis, measured by the continuous-infusion technique using [14C]proline, increased markedly during hypertrophy. This increase was mediated initially (after 1 day) by an increase in the RNA activity but at all other times reflected the higher RNA content. The rate of protein degradation, calculated from the difference between the synthesis and growth rates, appeared to increase and remain elevated for at least 4 weeks. At no time was there any suggestion of a fall in the rate of degradation. The following events are discussed as central to the changes that occur during skeletal-muscle hypertrophy. 1. Nuclear proliferation is necessary to maintain the characteristic synthesis rate because of the inability of existing nuclei to 'manage' increased protein synthesis for more than a limited period. 2. The increased protein breakdown during hypertrophy is consistent with the known over-production of a new muscle fibres and may indicate some 'wastage' during the growth. Such wastage may also be associated with myofibrillar proliferation. 3. Muscle stretch must be recognized as the major activator of growth and as such can be compared with the 'pleiotypic activators' that have been described for cells in culture.

Turnover of muscle protein in the fowl. Collagen content and turnover in cardiac and skeletal muscles of the adult fowl and the changes during stretch-induced growth

The collagen content and the rate of collagen synthesis were measured in the anterior and posterior latissimus dorsi muscles and in heart from fully grown fowl. This was done by measuring the proline/hydroxyproline ratios in the muscle and by a constant infusion of [(14)C]proline. These measurements were also made during the hypertrophy of the anterior muscle in response to the attachment of a weight to one wing of the fowl. In the non-growing muscles the collagen content was higher in the anterior muscle (22.8% of total protein) than in the posterior muscle (9.5% of total protein) and lowest in the heart (3.8% of total protein). In the two skeletal muscles a little over half of the collagen was accounted for by internal collagen (i.e. perimysium and endomysium). Collagen synthesis in these non-growing muscles occurred at 0.59%/day in each of the two skeletal muscles and at 0.88%/day in the cardiac muscle. During hypertrophy the collagen content of the anterior muscle increased, but not as fast as intracellular protein, so that after 58 days the concentration had fallen from 22.8 to 14.4% of total protein. This may have resulted from an incomplete production of the epimysial sheath, since the concentration of internal collagen did not fall and as a result accounted for over 80% of the total in the enlarged muscle. Collagen synthesis increased 8-fold during the first week of the hypertrophy, but never amounted to more than 4% of the total muscle protein synthesis. When the net accumulation of collagen is compared with the increased rate of synthesis it is concluded that between 30 and 70% of the newly synthesized collagen may have been degraded.

Turnover of muscle protein in the fowl (Gallus domesticus). Rates of protein synthesis in fast and slow skeletal, cardiac and smooth muscle of the adult fowl

Rates of protein synthesis in skeletal, cardiac and smooth muscle of fully grown fowl (Gallus domesticus) were determined in vivo by means of the constant infusion method using [14C]proline. In the anterior latissimus dorsi muscle, containing predominantly slow fibres, the average synthesis rate of non-collagen muscle proteins was 17.0 +/- 3.1% per day, a value higher than that obtained for cardiac muscle (13.8 +/- 1.3% per day) and for smooth muscle of the gizzard (12.0 +/- 1.9% per day). In the posterior latissimus dorsi muscle, containing predominantly fast fibres, synthesis rates were much lower (6.9 +/- 1.8% per day). In each case these average rates for the non-collagen protein were similar to the average rate for the sarcoplasmic and myofibrillar protein fractions. The RNA concentration of these four muscles showed that relative rates of protein synthesis were determined mainly by the relative RNA concentrations. The rate of protein synthesis per unit of DNA (the DNA activity) was similar in the two skeletal muscles, but somewhat lower in cardiac muscle and gizzard, possibly reflecting the larger proportion of less active cell types in these two muscles. These quantitative aspects of protein turnover in the two skeletal muscles are discussed in terms of the determination of ultimate size of the DNA unit, and in relation to muscle ultrastructure.

Turnover rates of muscle protein in cardiac and skeletal muscles of dog, fowl, rat and mouse: turnover rate related to muscle function

Turnover rates of muscle protein in cardiac and skeletal muscle have been measured in dogs using a continuous infusion of 14C-tyrosine, and in fowls, rats and mice after a pulse label of either 3H-leucine or 3H-aspartate. In all species the total mixed protein from ventricle turned over the most rapidly. Tonic muscles predominantly comprised of red fibres were intermediate in rate and twitch muscles comprised of predominantly white fibres had the slowest rates of turnover. This same progression of turnover rates was also seen in myofibrillar and sarcoplasmic protein fractions and with myosin. The RNA concentrations of the muscle tissue were highly correlated with the turnover rates. It is suggested that the turnover rate of muscle protein is related to the function of the muscle.

Changes in RNA, DNA and protein content and the rates of protein synthesis and degradation during hypertrophy of the anterior latissimus dorsi muscle of the adult fowl (Gallus domesticus)

Hypertrophy of the anterior latissimus dorsi muscle of the adult fowl was induced by attaching a weight to one wing and after 2, 6 and 14 days the muscle wet weight, as well as protein, RNA and DNA contents were measured. After 6 days of hypertrophy the wet weight of the muscle had increased by 74%, the protein content by 44%, RNA by 203% and DNA by 83% compared with the contralateral control. Average rates of protein synthesis and degradation were measured over the 14 days of hypertrophy from the rate of loss of radioactivity in the muscle protein after pulse labelling using 3H-leucine. Results were compatible with a 50% increase in the protein synthesis rate with no detectable change in the degradation rate. The increase in synthesis rate was paralleled by a similar rise in the RNA concentration. The DNA content indicated that this increase in RNA resulted from an increased RNA production per nucleus as well as from an increased number of nuclei. The kinetics of the loss of total radioactivity from the muscle protein and the amount of free 3H-leucine remaining in the muscle free amino acid pool during hypertrophy indicated that reutilization of 3H-leucine was extensive. This was in spite of attempts aimed at minimizing reutilization by feeding fowls a high protein diet plus a daily supplement of unlabelled leucine.

The effect of catecholamines on the in vivo and in vitro responses of the cat lung during anaphylaxis

1. Anaphylaxis in the lung of cats actively sensitized to Ascaris antigen has been investigated in vivo and in vitro. 2. In vivo there was a 100% increase in airways resistance and a 50% decrease in dynamic lung compliance following intravenous challenge with Ascaris antigen. Prostaglandin F2alpha induced similar changes but with histamine only dynamic lung compliance was affected. (-)-Isoprenaline prevented these prostaglandin F2alpha- and histamine-induced changes and caused a delay of about 2 min in the onset of the mechanical changes following anaphylactic challenge. 3. In vitro the isolated lung strip contracted within seconds of challenge whereas there was a delay of 2 to 3 min in the onset of the tracheal anaphylactic response. (-)-Isoprenaline, (-)-adrenaline and (+/-)-noradrenaline reduced the magnitude of anaphylactic contractions of the isolated trachea but did not significantly affect those of the isolated lung strip. This indicated lack of inhibition of mediator release from the lung parenchyma. 4. Histamine was released from sensitized lung fragments following challenge with the Ascaris extract. This release constituted 6.3% of the total tissue histamine and was not inhibited by (-)-isoprenaline (1 micrometer). 5. (-)-Isoprenaline abolished 5-hydroxytryptamine (5-HT)-induced contractions of the isolated trachea but not those elicited in response to acetylcholine. The isolated lung strip responses to histamine, prostaglandin F2alpha and 5-HT were highly resistant to inhibition by (-)-isoprenaline.

Protein synthesis during right-ventricular hypertrophy after pulmonary-artery stenosis in the dog

The rate of protein synthesis in the heart of normal dogs and those with pulmonary-artery stenosis was measured by a continuous intravenous infusion of [14C]tyrosine. The protein-synthesis rate of both ventricles was the same in normal dogs and averaged 7.5% per day. The right ventricle hypertrophied rapidly after the acute imposition of pulmonary-artery stenosis, the wet weight increasing by 84% after 24 days, with the rate of increase being most rapid over the first 5 days. The left ventricle remained largely unaffected and served as an internal control. During hypertrophy there was an increased incorporation of [14C]tyrosine into protein without a significant change in the specific radioactivity of free tyrosine in the ventricles. After 5 days of stenosis the synthesis rate of the total mixed proteins of the right ventricle had increased to 13.6% per day, compared with 6.2% in the control left ventricle. This increase in synthesis was reflected in both the myofibrillar and sarcoplasmic proteins. After 5 days the protein-synthesis rate decreased, but still remained significantly elevated above that in the control left ventricle by 24 days of stenosis.

The cat lung strip as an in vitro preparation of peripheral airways: a comparison of beta-adrenoceptor agonists, autacoids and anaphylactic challenge on the lung strip and trachea

1 A new in vitro preparation, the isolated lung strip of the cat, is described for investigating the direct effect of drugs on the smooth muscle of the peripheral airways of the lung. The preparation comprises a thin strip of lung parenchyma which can be mounted in a conventional organ bath for isometric tension recording. Its pharmacological responses have been characterized and compared with the isolated tracheal preparation of the cat. 2 The lung strip exhibited an intrinsic tone which was relaxed by catecholamines, aminophylline and flufenamate. It was contracted strongly by histamine, prostaglandin F2alpha, acetylcholine, compound 48/80, potassium depolarizing solution and alternating current field stimulation. In contrast, the cat trachea was unresponsive to histamine and prostaglandin F2alpha and did not exhibit an intrinsic tone. 3 (-)-Isoprenaline and (-)-adrenaline were much more potent in relaxing the lung strip than the trachea. The potency order of relaxation responses to isoprenaline, adrenaline and (+/-)-noradrenaline in the lung strip was isoprenaline greater than adrenaline greater than noradrenaline but in the trachea was isoprenaline greater than noradrenaline greater than or equal to adrenaline. 4 beta2-Adrenoceptor selective agonists salbutamol and terbutaline were more potent in the lung strip than the trachea, suggesting beta2-adrenoceptors predominated in the lung strip. Propranolol was equipotent in inhibiting isoprenaline relexations of the lung strip and trachea, whereas practolol was much less effective in inhibiting lung strip than trachea, further supporting a predominance of beta2-adrenoceptors in lung strip and beta1-adrenoceptors in trachea. 5 Strong Schultz-Dale type contractions were elicited in both lung strips and trachea by Ascaris lumbricoides antigen in actively sensitized cats. The initial phase of the contractile response of the lung strip following challenge was shown to be due to histamine release and was absent in the trachea. The delayed phase of the contraction which took several minutes to develop in both the mepyramine-treated lung strip and trachea was not due to prostaglandins E1, F2alpha or bradykinin, the probable mediator being slow reacting substance of anaphylaxis (SRS-A). 6 It is concluded that the isolated lung strip of the cat is useful as an in vitro model for investigating the effect of drugs on the smooth muscle of the peripheral airways of the lungs.

Increased protein synthesis during right ventricular hypertrophy following pulmonary stenosis in the dog

The synthesis rates of mixed protein in the left and right ventricles were the same in normal dogs, averaging 7.8% per day. After five days, pulmonary stenosis protein synthesis rate in the right ventricle increased rapidly to 13.6% per day and subsequently decreased to near normal by 12 days, during which time the right ventricle protein mass increased by 48% after five days and by 73% after 12 days. Similarly the synthesis rate of the myofibrillar and sarcoplasmic proteins was almost doubled after five days of stenosis. The protein synthesis rate in the left ventricle did not change significantly during the 24 days of pulmonary stenosis.

Turnover rates of muscle proteins in cardiac, skeletal, and smooth muscle: turnover rate related to muscle function

The turnover rate of muscle proteins was related to the physiological function of the muscle in dogs, fowl, rats, and mice. The turnover rates of mixed muscle proteins were most rapid in cardiac muscle, intermediate in red tonic and mixed fiber-type muscles, and slowest in white twitch skeletal muscle. This same progression in turnover rates also was shown in the subcellular fractions of muscle-sarcoplasmic and myofibrillar proteins-as well as in purified proteins, myosin, and tropomyosin. The RNA concentration of muscle was highly correlated with the protein turnover rate, and the RNA activity, i.e., the translational efficiency of the RNA, was similar in the different muscle types.

Interaction of 28Mg with Ca and K in the smooth muscle of guinea-pig taenia coli

1. The uptake of (28)Mg, and the total tissue content of Mg, Ca, Na and K have been determined in the smooth muscle of the guinea-pig taenia coli. The Mg content was 6.56 m-mole/kg fresh wt. immediately after dissection, falling slowly to 5.11 after 6 hr immersion in Krebs solution at 37 degrees C.2. The Mg content rose to 15.4 m-mole/kg fresh wt. during immersion in isotonic sucrose containing only MgCl(2). It was independent of the Mg(2+) concentration in this solution, but was depressed when K(+) or Ca(2+) ions were added.3. (28)Mg uptake showed three separate phases, extracellular, intermediate and slow. The size of the extracellular phase was proportional to the Mg(2+) concentration in the solution, but the size of the slow phase was constant. The size of the intermediate phase, exchanging with a half-time of a few minutes, was depressed when K(+) or Ca(2+) ions were added.4. The results are compatible with a competition between Mg in the intermediate phase of tracer exchange, and K(+) or Ca(2+) ions for fixed anionic sites in the tissue.