Existence of parvalbumin and biochemical characterization in quail and pigeon skeletal muscles with different fiber type compositions

The effects of intraperitoneal clenbuterol injection on protein degradation and myostatin expression differ between the sartorius and pectoral muscles of neonatal chicks

The purpose of this study was to investigate the effects of injection of the β2-adrenergic receptor agonist clenbuterol on the skeletal muscles of neonatal chicks (Gallus gallus domesticus). One-day-old chicks were randomly divided into four groups and given a single intraperitoneal injection of clenbuterol (0.01, 0.1, or 1mg/kg) or phosphate-buffered saline. Twenty-four hours after the injection, the sartorius muscles (which consist of both slow- and fast-twitch fibers) of chicks that received 0.01 or 0.1mg/kg clenbuterol were significantly heavier than those of controls, while there were no between-group differences in the weight of the pectoral muscles, which consist of only fast-twitch fibers. Muscle free N(t)-methylhistidine, regarded as an index of myofibrillar proteolysis, was decreased in the sartorius muscle of the clenbuterol-injected chicks, while it was not affected in the pectoral muscles. In the sartorius muscle of the clenbuterol-injected chicks, myostatin and atrogin-1/MAFbx mRNA expressions were decreased, while insulin-like growth factor-I was unaffected. These observations suggested, in 1-day-old chicks, clenbuterol might increase mass of the sartorius muscle by decreasing myostatin gene expression and protein degradation.

Role of prolactin-like protein (PRL-L) in cold-induced increase of muscle mass in chicks

This study examined the hypothesis that a novel prolactin-like protein gene (PRL-L) is involved in cold-induced growth of skeletal muscle in chicks. Six-day-old chicks (Gallus gallus domesticus) were exposed to cold at 4°C or kept warm at 30°C for 24h. Cold exposure induced significant increases in PRL-L expression that coincided with increases in the weight of the sartorius muscle, which comprises both fast- and slow-twitch fibers. Meanwhile, no induction of PRL-L mRNA was observed in the heart, liver, kidney, brain, or fat. Myoblast cells that expressed PRL-L mRNA grew faster than untransduced cells in media containing 2% serum. These results suggested that PRL-L might be involved in in controlling cold-induced muscle growth of chicks.

Increased expression of NOR-1 mRNA in the skeletal muscles of cold-exposed neonatal chicks

Nuclear receptor subfamily 4, group A (NR4A) subgroup orphan receptors are rapidly induced by various physiological stimuli and have been suggested to regulate oxidative metabolism and muscle mass in mammalian skeletal muscle. The results showed that the NR4A subgroup orphan receptor, NOR-1 (NR4A3), was acutely increased in skeletal muscles of neonatal chicks in response to short-term cold exposure. The increased NOR-1 gene expression was concomitant with cold-induced changes in gene expression of both myostatin and proliferator-activated receptor-gamma coactivator-1 (PGC-1α), and the increase in skeletal muscle mass. These observations suggest that NOR-1 might play a role in controlling skeletal muscle growth in cold-exposed neonatal chicks.

Muscle designed for maximum short-term power output: quail flight muscle

Take-off in birds at high speeds and steep angles of elevation requires a high burst power output. The mean power output of the pectoralis muscle of blue-breasted quail (Coturnix chinensis) during take-off is approximately 400 W kg-1 muscle, as determined using two independent methods. This burst power output is much higher than has been measured in any other cyclically contracting muscle. The power output of muscle is determined by the interactions between the physiological properties of the muscle, the stimulation regime imposed by the central nervous system and the details of the strain cycle, which are determined by the reciprocal interaction between the muscle properties and the environmental load. The physiological adaptations that enable a high power output to be achieved are those that allow the muscle to develop high stresses whilst shortening rapidly. These characteristics include a high myofibrillar density, rapid twitch contraction kinetics and a high maximum intrinsic velocity of shortening. In addition, several features of the strain cycle increase the power output of the quail pectoralis muscle. First, the muscle operates at a mean length shorter than the plateau of the length/force relationship. Second,the muscle length trajectory is asymmetrical, with 70 % of the cycle spent shortening. The asymmetrical cycle is expected to increase the power output substantially. Third, subtle deviations in the velocity profile improve power output compared with a simple asymmetrical cycle with constant lengthening and shortening rates. The high burst power outputs found in the flight muscles of quail and similar birds are limited to very brief efforts before fatigue occurs. This strong but short flight performance is well-suited to the rapid-response anti-predation strategy of these birds that involves a short flight coupled with a subsequent sustained escape by running. These considerations serve as a reminder that the maximum power-producing capacities of muscles need to be considered in the context of the in vivosituation within which the muscles operate.