Muscle contraction prolongation

Binding of epinephrine to the (3-adrenergic receptors in heart muscle stimulates glycogenolysis and enhances the rate of muscle contraction. Prolonged treatment with epinephrine, however. Induces proliferation of these cardiac muscle cells. In extreme cases, such cardiac by pertrophy causes failure of the heart muscle, a major cause of heart disease. This eplnephrlne-lnduced cell proliferation results... 

This acts presynaptically, via activation of ATP-sensitive potassium channels, to inhibit neuromuscular transmission and acts at the muscle membrane to inhibit muscle contraction. Prolongation of neuromuscular block has been reported in patients receiving lithium and depolarizing and non-depolarizing neuromuscular blockers. Hence, the combination of litbium and ECT is relatively contraindicated. 

Explain why smooth muscle contraction is slow and prolonged... 

Contraction of smooth muscle is significantly slower than that of skeletal muscle. Furthermore, smooth muscle contraction is quite prolonged (3000 msec) compared to that in skeletal muscle (100 msec). The slow onset of contraction as well as its sustained nature is due to the slowness of attachment and detachment of the myosin crossbridges with the actin. Two factors are involved ... 

Within 30 minutes of their administration, 6 -adrenergic drugs often reverse most of the functional deficit in Monday morning byssinotics. As there is no mucous secretion, airway smooth muscle contraction is considered the primary response. Exposure of man to histamine aerosols produces pulmonary function changes similar to those seen after exposure to dust extract. However, exposure to histamine aerosol invariably initiates constriction of smooth muscle more rapidly than exposure to cotton dust ( <15 minutes), and dissipates within minutes, while the acute effects of inhalation of cotton dust and dust extracts lasts for hours. The slowly developing and prolonged effects of dust and extracts suggest that mediators other than histamine are involved. 

Substances that block the serine residue in the active center of acetylcholinesterase [2j—e.g., the neurotoxin E605 and other organophosphates—prevent ACh degradation and thus cause prolonged stimulation of the postsynaptic cell. This impairs nerve conduction and muscle contraction. Curare, a paralyzing arrow-poison used by South American Indians, competitively inhibits binding of ACh to its receptor. 

Ergotamine Mixed partial agonist effects at 5-HT2 and (X adrenoceptors Causes marked smooth muscle contraction but blocks cx-agonist vasoconstriction Migraine and cluster headache Oral, parenteral duration 12-24 h Toxicity Prolonged vasospasm causing gangrene uterine spasm... 

Succinylcholine Agonist at nicotinic acetylcholine (ACh) receptors, especially at neuromuscular junctions depolarizes may stimulate ganglionic nicotinic ACh and cardiac muscarinic ACh receptors Initial depolarization causes transient contractions, followed by prolonged flaccid paralysis depolarization is then followed by repolarization that is also accompanied by paralysis Placement of tracheal tube at start of anesthetic procedure t rarely, control of muscle contractions in status epilepticus Rapid metabolism by plasma cholinesterase normal duration, 5 min Toxicities Arrhythmias hyperkalemia transient increased intraabdominal, intraocular pressure postoperative muscle pain... 

Causes release of Ca from muscle storage sites this leads to muscle contraction. Inhibits return of Ca to storage sites, prolonging muscle contraction. 

Glycogen is stored mainly by the liver and skeletal muscle as an energy reserve. The role of stored glycogen in muscle is to provide a source of energy upon prolonged muscle contraction. In contrast, glycogen stored in the liver is used to maintain blood glucose levels. 

Histrionicotoxin is a defensive toxin that protects Dendrobates histrionicus from potential predators. These small poison dart frogs inhabit the moist humid floor of tropical rainforests, and are commonly found in western Ecuador and Colombia. Histrionicotoxin acts by interfering with nerve transmission in mammals, resulting in prolonged muscle contraction. 

Rhabdomyolysis may result from prolonged pressure on muscles, from agents that cause muscle spasm or convulsions (phencyclidine, theophylline) or be aggravated by hyperthermia due to muscle contraction, e.g. with MDMA ( ecstasy ). Aggressive volume repletion and correction of acid-base abnormality may be needed, and urine alkalinisation may prevent acute tubular necrosis. 

The effects of non-depolarizing neuromuscular blocking drugs can be potentiated and their actions prolonged by large doses of local anesthetics, because of depression of nerve conduction, inhibition of acetylcholine formation, mobilization, and release, reduced postsynaptic receptor channel opening times, and reduced muscle contraction (370). 

Skeletal muscle is specialized to perform intermittent mechanical work. As described previously, the energy sources that provide ATP for muscle contraction depend on the degree of muscular activity and the physical status of the individual. During fasting and prolonged starvation, some skeletal muscle protein is degraded to provide amino acids (e.g., alanine) to the liver for gluconeogenesis. 

Physiologically, early reinnervation is marked by polyphasic nerve and muscle potentials, due to the polyneuronal innervation. Muscle contractions are weak and slow, with a prolonged rate of rise to peak amplitude, all characteristics of the immature neuromuscular system. With time, more complete reinnervation occurs, and many of the contractile... 

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