Calcium regulation of skeletal myogenesis. I. Cell content critical to myotube formation

Primary cultures of embryonic chick pectoral skeletal muscle were used to study calcium regulation of myoblast fusion to form multinucleated myotubes. Using atomic absorption spectrometry to measure total cellular calcium and the 45Ca-exchange method to determine free cellular Ca++, our data suggest that only the free cellular calcium changes significantly during development under conditions permissive for myotube formation (0.9 mM external Ca++). Increases in calcium uptake occurred before and toward the end of the period of fusion with the amount approximating 2 to 4 pmol per cell in mass cultures. If the medium [Ca++] is decreased to 0.04 mM, as determined with a calcium electrode, a fusion-block is produced and free cell Ca++ decreased 5- to 10-fold. Removal of the fusion-block by increasing medium [Ca++] results in a release of the fusion-block and an increase in cellular Ca++ to approximately 1 pmol per cell during fusion, and higher thereafter. Cation ionophore A23187 produced transient increases in cellular calcium and stimulated myoblast fusion and the final extent of myotube formation only when added at the onset of culture. Results suggest that transient increased calcium uptake alone is insufficient for fusion because critical cellular content in conjunction with permissive amounts of medium [Ca++] must exist. The latter suggests further that cell surface Ca++ was also critical.

Recombinant growth hormone in growing lambs: effects on growth, body and carcass characteristics, hormones and metabolites

Forty-eight crossbred wethers [Dorset Horn X (Border Leicester X Merino)] were injected subcutaneously each day for 42 to 133 days with recombinant bovine growth hormone (rebGH) at doses of either 0,50,150 or 250 pg rebGH kg-1 liveweight day-1 from 22 kg liveweight (LW) until slaughter at either 34, 42 or 50 kg LW. The lambs were fed ad libitum pellets consisting of (g kg-1 as fed) 850 lucerne, 100 barley and 50 cotton seed meal.Injections of rebGH exerted anabolic effects which were dose dependent. Overall, there were linear increases (P<0.001) in liveweight gain (LWG), total non-carcase weight, weights of heart, liver, skin, reticula-rumen, loin eye area, carcase crude protein, non-carcase crude protein, carcase ash and noncarcase ash, as well as plasma concentrations of insulin and glucose (P<0.01). There were linear decreases (P< 0.001) in feed conversion ratio, carcase weight, tissue depth (GR) and subcutaneous fat depth at the 12th rib, carcase fat and non-carcase fat as well as plasma urea. Significant interactions of dose rate with liveweight groups indicated that overall, the effects were larger in sheep grown to 50 kg than to 34 kg LW, or occurred only in the former in respect of weights of carcase, heart, liver and reticula-rumen. The same was true for depth of tissue, depth of subcutaneous fat and loin eye area at the 12th rib and also carcase and non-carcase weights of CP, fat and ash.

Effects of growth hormone administration on wool growth in merino sheep

The effects of daily administration of 10 mg of highly purified ovine growth hormone (GH) for a period of 4 weeks on wool growth have been measured in 12 Merino ewes fed either a calculated maintenance energy intake or 1.6 times this amount (six on each ration). Concentrations of hormones, glucose, urea, alpha-amino N and amino acids in the blood were monitored and faeces and urine collected for measurement of nitrogen balance. Wool growth rate decreased by 20% during the 4 weeks of GH treatment in sheep fed the high energy diet, largely because of reduced wool fibre diameter. This was followed by restoration of normal growth and then an increase of up to 20% above control levels, a response which persisted for 12 weeks following cessation of GH administration, and which was due to increases in both fibre length and diameter. GH administration caused marked increases in plasma concentrations of GH, insulin and somatomedin C, glucose and free fatty acids, all of which returned to basal levels following cessation of GH administration. No consistent changes in plasma concentration of T3, T4, cortisol, prolactin or alpha amino N were detected. Plasma urea and methionine levels decreased during GH treatment and returned to, or were raised above, basal levels after the GH treatment period. GH injection also resulted in a net retention of N during treatment, followed by a transient period of net N loss. The GH-induced changes in wool growth may be caused by a change in the partitioning of amino acids between the muscle mass and the skin. No other contributing factor(s) were identified.

Effects of pituitary-derived bovine growth hormone on production parameters and biokinetics of key metabolites in lactating dairy cows at peak and mid-lactation

Changes in production parameters and metabolite biokinetics induced by treatment with pituitary-derived bovine growth hormone (bGH) were monitored at peak (c. 40 days) and mid-lactation (c. 130 days) in dairy cows. During treatment with bGH milk production increased by 6 and 14% at peak and mid-lactation respectively. At peak lactation the content of milk fat tended to increase, whereas milk protein tended to decrease and milk lactose decreased significantly. Yield of milk fat increased, but there was no change in the yield of milk protein and lactose. The content of milk fat tended to increase at mid-lactation. Milk protein decreased and there was no change in milk lactose. Yields of milk fat and lactose but not protein increased. Growth hormone exerted metabolic effects which differed with stage of lactation. At peak lactation plasma glucose concentration and its irreversible loss increased, plasma urea and acetate were unchanged and their irreversible losses tended to increase. No change was measured for plasma non-esterified fatty acids (NEFA) and the irreversible loss of NEFA decreased. At mid-lactation plasma concentrations of glucose and NEFA were increased, plasma urea decreased and acetate and 3-hydroxybutyrate tended to increase. Irreversible losses of NEFA increased, urea tended to decrease and acetate and glucose remained essentially constant. The results show that exogenous pituitary bGH exerts metabolic effects which result in the supply of increased nutrients to support milk synthesis. The metabolic effects differ with the stage of lactation, reflecting differences in physiological and/or nutritional state.

Local intra-arterial infusion of growth hormone into the mammary glands of sheep and goats: effects on milk yield and composition, plasma hormones and metabolites

Lactating goats and sheep were fitted with catheters in the external pudendal arteries supplying both mammary glands. Saline was infused continuously into one artery whereas the other artery received continuous infusions, over successive 4-day periods, of either saline or growth hormone (GH)-doses increasing twofold between successive periods from 100 to 400 micrograms/day in goats and 400 to 3200 micrograms/day in sheep. Local infusion of GH at up to 1600 micrograms/day in sheep did not affect milk yield or composition nor peripheral plasma concentrations of GH, insulin, glucose, urea and non-esterified fatty acids (NEFA). Infusion of GH at 3200 micrograms/day in sheep increased peripheral plasma concentrations of GH, tended to increase milk yield and peripheral plasma NEFA but there were no changes in peripheral plasma insulin, glucose and urea. It is concluded that GH does not exert direct effects on the mammary glands of sheep and goats in situations where the hormone is administered over short periods.

Calcium regulation of skeletal myogenesis: IV. A defined culture medium permissive for myotube formation and the use of the calcium antagonist lanthanum

Lanthanum has been used effectively in studies of calcium physiology in experiments of short duration. In experiments of longer duration, we report that solutions, such as cell culture medium, containing lanthanum (La++) undergo a decrease in pH on the time scale of hours. Presumably, the decrease in pH is a consequence of the hydrolysis of water by the solution-active La ions. We have devised a defined culture medium without serum and chick embryo extract which is permissive for myotube formation. This defined medium is also useful for studies of La as a calcium antagonist. La at concentrations of 0.1 mM reversibly inhibits myotube formation when added in conjunction with Ca++ to low-Ca++ fusion-blocked cultures.

Supplemental protein degradation, bacterial protein synthesis and nitrogen retention in sheep eating sodium hydroxide-treated straw

1. Alkali (sodium hydroxide)-treated wheat straw was given to six rumen- and abomasal-cannulated sheep to study the rumen degradation of cotton-seed meal (CSM) and barley (B), and the effects of these supplements on nitrogen retention and efficiency of bacterial protein synthesis were measured. 2. N degradation, using porous synthetic (nylon) bags incubated within the rumen (P), and in vivo measurement determined from the abomasal flow of N (V), distinguished quantitatively between the two supplements. Estimates of P, corrected for fractional outflow rates/h (FOR), underestimated estimates of V when FOR of undegraded protein from the rumen (k) of 0.05 and 0.08 were used. Estimates of V for CSM and B were 70.9 and 80.8% respectively. 3. Intakes of alkali-treated straw were not affected by the supplements. Intakes of digestible organic matter (DOM) for the diets comprising alkali-treated straw alone (W), straw plus CSM (WC) and straw plus barley (WB) were 477, 575 and 590 g/d respectively (P less than 0.05) and organic matter (OM) apparently digested in the rumen (OMADR) was 339, 399 and 435 g/d respectively (P less than 0.05). 4. On W, WC and WB respectively, flows at the abomasum were 11.0, 14.0 and 13.3 g/d for bacterial N (P less than 0.05) and 0, 2.8 and 0.5 g/d for dietary supplemental N; g bacterial N/kg OMADR were 32.4, 35.6 and 30.9 (P greater than 0.05) and N balances were 2.37, 4.27 and 3.29 g/d (P less than 0.05) on the respective treatments. It was suggested that supplements increased total OM intake as a result of increased OM digested in the rumen rather than OM flow from the rumen.

Rumen degradation and fractional outflow rates of nitrogen supplements given to cattle eating sodium hydroxide-treated straw

1. Six rumen and abomasal cannulated heifers were used to study the effects of intake on the fractional outflow rates (FOR) of chromium-mordanted cotton-seed meal (Cr-CSM) and meat meal (Cr-MM), CrEDTA, ytterbium and lignin from the rumen. Values of FOR of Cr-CSM and Cr-MM were combined with values of nitrogen disappearance from the protein supplements, placed in porous synthetic (nylon) bags and incubated within the rumen (P), to calculate effective degradation (D) of CSM and MM when fed to heifers eating sodium hydroxide-treated straw. Also, N degradation in vivo (V) was measured as the difference between abomasal N flow and the sum of flows of microbial and endogenous N. 2. FOR were positively related to intake and differences between supplements were significant (P less than 0.01). FOR pertaining to high and low intakes respectively were 0.073 and 0.052 for Cr-CSM, 0.082 and 0.071 for Cr-MM, 0.030 and 0.023 for lignin, 0.082 and 0.073 for CrEDTA and 0.044 and 0.035 for Yb. 3. A rise of 28.8 and 13.4% in FOR of Cr-CSM and Cr-MM respectively, associated with an increase in intake from maintenance to 1.5 times maintenance, resulted in 10.7 and 2.2% reductions in D, 24 h after feeding, for CSM and MM respectively. 4. With the exception of CSM at the high intake, estimates of V were underestimated by D and were 8.6-25.0% greater than the D values when time of incubation (t) = infinity. The two techniques, however, ranked the degradation of the two supplements in the same order at both levels of intake. 5. Underestimation of V by D may be attributable to underestimation of P, overestimation of FOR (both resulting in underestimation of D) or overestimation of V due to biases associated with the estimation of this part of the comparison. The relative importance of these factors remains to be determined.

The utilization by pigs of methionine from five protein concentrates compared with synthetic methionine

Pigs (n 100) between 28 and 56 d of age were given diets containing one of five protein concentrates ad lib. The utilization of methionine from the protein concentrates was compared with synthetic methionine. Increasing the methionine content of the diets from 1.5 to 2.2 g/kg diet increased the weight gains of the pigs from 61 g/d to 198-292 g/d. The feed conversion efficiencies decreased from 2.56 to 1.34-1.56. The utilization of methionine from the protein concentrates for weight gain, as compared with synthetic methionine, was meat meal A 0.89, meat meal B 0.97, soya-bean meal 1.02, cotton-seed meal 0.87 and dried skim milk 1.04.

Germination and seedling growth of prairie grass, tall fescue and Italian ryegrass at different temperatures

We measured the effects of temperature on the germination, emergence and growth during early tillering of Italian ryegrass (Lolium multiflorum), prairie grass (Bromus catharticus) and tall fescue (Festuca arundinacea). Radicle emergence (the percentage of seeds with emerged radicles) and 'field' emergence (the percentage of seeds with shoots > 1 cm long) were reduced at 35�C (constant, all lines), or 30/25�C (12/12 h, prairie grass and Tama Italian ryegrass only). All lines took longer to germinate at 15 and 10�C (constant) than at higher temperatures, and final percentage germination of tall fescue lines was lower at 10�C (constant) than at other temperatures. Italian ryegrass had the fastest shoot extension, and consequently the fastest 'field' emergence. Seed respiration rates were higher in fescue than in the other lines at 4 days from imbibition, and rates rose in all lines at 8 days. Over the first 20 days after sowing, growth rates were closely related (r = 0.87-0.99) to weights of seed and caryopses, when account was taken of perenniality (which was associated with relatively slow growth) and polyploidy (which was associated with growth faster than might be expected from seed size alone), and a multivariate relationship including temperature was developed (R2 = 0.88). Growth rates of shoots at 20 days after sowing were ranked Tama Italian ryegrass > prairie grass > Ucivex Italian ryegrass > tall fescue, and 24/19 > 21/16 > 18/13 > 30/25 > 15/10�C. Growth during tillering, up to 42 days after emergence, was ranked Italian ryegrass > prairie > tall fescue and 21/16 = 18/13 > 24/19 = 15/1O�C. Relative growth rates and relative rates of tillering were independent of temperature in Italian ryegrass, but were lower at 15/10 and 24/19 than at 21/16 and 18/13�C in prairie grass and tall fescue. Prairie grass had higher yield per tiller but lower tiller numbers than Italian ryegrass; tall fescue had both lower yield per tiller and lower tiller number. Italian ryegrass was therefore the species best adapted to variations in environment and competition at sowing.

Responsiveness to seasonal temperature and nitrogen among genotypes of kikuyu, paspalum and bermuda grass pastures of coastal New South Wales

Three experiments were carried out to test the hypotheses that (a) there are quantitative differences in growth rate and quality between newly registered cultivars and older cultivars in response to changes in temperature and fertility, and (b) responsiveness to temperature varies between sites because cultivars acclimatize to their current environment. Performance in simulated swards indicated that potential productivity was highest from bermuda grass (Cynodon x Burton Pearson). This was, however, a poor indicator of performance in the field, where yield of bermuda grass was depressed by weeds whereas that of kikuyu (Pennisetum clandestinum) was unaffected. In the field, a newly registered kikuyu, cv. Crofts, outyielded bermuda grass and paspalum (Paspalum dilatatum) either alone or when combined with lucerne. A further experiment compared cvv. Crofts, Whittet and common kikuyu at three levels of nitrogen at three sites. Peak growth rates were the same at all locations but Crofts outyielded the other genotypes by 60, 13 and 18% at Bega (37�S.), Camden (34�S.) and Taree (32�S.) respectively. Average growth rates varied seasonally and were correlated with temperature (r > 0.9). Analysis of temperature responsiveness (kg/ha.�C) indicated that responsiveness varied consistently between genotypes at any location. Furthermore, the base temperature (the temperature below which there was negligible growth) was the same for all genotypes at any location but it increased with increasing latitude. That is, there was a tendency to greater dormancy with increasing coldness of location. Nitrogen responsiveness was the same for all genotypes and sites. Seasonal variations in digestibility and mineral concentrations in kikuyu, bermuda grass and paspalum were similar in the field and in simulated swards; quality was the same in all kikuyu genotypes. Calcium, magnesium and nitrogen concentrations of plant tops (but not phosphorus and potassium concentrations) increased with increasing rates of application of nitrogen fertilizer.

Effects of hypertonic solutions on contraction of frog tonic muscle fibers

The influence of solution hypertonicity on contraction was studied in small bundles of tonic muscle fibers from the iliofibularis muscle of the frog Rana pipiens. Muscles were activated with high-K+ solutions that had osmolalities which were increased with tris(hydroxymethyl)aminomethanepropionate. Peak potassium contracture force decreased monotonically with tonicity and was zero in solutions with 2.5 or 3 times the osmolality of control Ringer. Contracture force at all tonicities studied (less than or equal to 3 X Ringer) was increased by increasing Ca2+ in the media 10-fold (to 20 mM) and/or by adding caffeine (10-20 mM). Nevertheless, this potentiated force also was diminished as tonicity increased. Force of single, mechanically skinned tonic fibers taken from these bundles was activated by Ca2+ over the same concentration range as that of twitch fibers. Moreover, maximal Ca2+-activated force, normalized per cross-sectional area, was similar in skinned tonic and twitch fibers. As was shown previously in twitch fibers, maximal Ca2+-activated force was decreased when ionic strength was increased. These data suggest that, as with twitch fibers, increased tonicity depresses contraction of tonic fibers by increasing the intracellular ionic strength, which in turn inhibits the ability of the contractile apparatus to generate force. Unlike twitch fibers, however, disruption of the excitation-contraction coupling process probably plays a more significant role in the action of hypertonicity on tonic fibers.

Physiology of the sternoradialis muscle: sexual dimorphism and role in amplexus in the Leopard frog (Rana pipiens)

1. The role of upper arm muscles in amphibian amplexus was investigated. 2. The musculature of the male frog is arranged so that the response to any form of massive stimulation is flexion of the forelimbs, the fundamental pattern in amplexus. 3. The sternoradialis, one of the forelimb flexors, exhibited several sexually dimorphic characters. It was found to be larger in males than females and possessed a large population of small diameter muscle fibers. 4. Mechanical evidence indicated that the male sternoradialis contains a significant number of tonic or slow muscle fibers. These tonic fibers undergo physiological changes during amplexus including a membrane potential shift in the direction of the mechanical threshold and greater efficiency of contraction. 5. It was concluded that the sternoradialis contributes significantly to muscular response in amplexus and that the tonic fibers in this muscle play an important role in amplexus.

Calcium content and exchange in frog skeletal muscle

Calcium content and exchange in frog ELD IV muscle were examined employing the efflux technique. 2. Muscle calcium was found to exchange with four time constants, 21-5 sec 2-7, 32 and 1244 min. 3. All calcium was found to be exchangeable with more than half the total amount residing in an extracellular compartment. 4. Results obtained from ELD IV muscles and single fibres were identical. 5. Muscle calcium content was found to remain constant up to 20 hr in vitro. 6. Extra exchange of calcium occurs upon contraction. This extra exchange appears to occur in the most slowly exchanging component. 7. The data are discussed in relation to morphological and autoradiographic findings and a model of calcium exchange in skeletal muscle is presented.