Muscle cell membrane, permeability

Studies have led to evidence suggesting that two types of Na+ transport mechanisms may be defective in vascular smooth muscle cells in some forms of hypertension. These are (a) an increased cell membrane permeability to Na+, and (b) decreased active pumping of Na+ at the prevailing intracellular Na+ concentration, resulting from elevated blood levels of an endogenous inhibitor of the Na+-K+-ATPase, the so-called natriuretic hormone. The increase in intracellular Na+ concentration, in turn, promotes Ca2+ influx by the operation of the Na+/Ca2+ exchanger... 

In muscular dystrophy, therefore, the maintenance of considerable serum activities of soluble enzymes almost certainly of sarcoplasmic origin, and known to be subject to very rapid and continuous clearance from serum, strongly argues their ceaseless copious discharge from dystrophic muscle. The likelihood at once arises that the dystrophic muscle cell membrane is unduly permeable to these enzymes, that their activities are diminished within the cell, and that because of such lavish discharge even reduced intracellular activities could be preserved only by unusually rapid renewal. These probabilities receive substantial support from the results obtained by other workers. 

In conclusion, some of the most important observations made on insulin s mechanism of action in muscle can be summarized as follows the intracellular concentration of glucose is increased after insulin administration insulin stimulates the transport of metabolizable and nonmetabolizable sugars with an identical configuration in carbons 1, 2, and 3 and different sugars compete for the site of action of insulin. On the basis of such observations, it has been suggested that insulin promotes sugar transport through the muscle cell membrane by activation of a specific transfer system rather than by an increase in membrane permeability. 

The membranes of nerve cells contain well-studied ion channels that are responsible for the action potentials generated across the membrane. The activity of some of these channels is controlled by neurotransmitters hence, channel activity can be regulated. One ion can regulate the activity of the channel of another ion. For example, a decrease of Ca + concentration in the extracellular fluid increases membrane permeability and increases the diffusion of Na+. This depolarizes the membrane and triggers nerve discharge, which may explain the numbness, tinghng, and muscle cramps symptomatic of a low level of plasma Ca. ... 

Each cell is surrounded by a plasma membrane that separates the cytoplasmic contents of the cell, or the intracellular fluid, from the fluid outside the cell, the extracellular fluid. An important homeostatic function of this plasma membrane is to serve as a permeability barrier that insulates or protects the cytoplasm from immediate changes in the surrounding environment. Furthermore, it allows the cell to maintain a cytoplasmic composition very different from that of the extracellular fluid the functions of neurons and muscle cells depend on this difference. The plasma membrane also contains many enzymes and other components such as antigens and receptors that allow cells to interact with other cells, neurotransmitters, blood-borne substances such as hormones, and various other chemical substances, such as drugs. 

All cell membranes contain transmembrane proteins that form ion channels. These ion channels are usually selectively permeable to particular ions. Some channels, such as GABA-gated ion channels, are permeable to Cl ions and are inhibitory in nature because they make the inside of the nerve or muscle cells more negative as the Cl ions enter. Some ion channels are permeable to the cations Na and K, and an example of this type is the nicotinic acetylcholine-gated channel. Nicotinic channels have an excitatory effect when they open because Na ions enter and K ions leave through these channels. The cell becomes more positive inside and depolarizes. If the cell is a muscle cell, calcium accumulates in the cytoplasm and it contracts. We have found that all over the surface of Ascaris muscle there are GABA receptors (Martin, 1980) as well as nicotinic acetylcholine channels (Martin, 1982 Robertson and Martin, 1993). 

Ivermectin binds selectively and with high affinity to glutamate gated chloride ion channels in invertebrate nerve and muscle cells. This leads to an increase in the permeability of cell membrane to chloride ions with hyperpolarization of nerve of muscle cell, resulting in paralysis and death of the parasite. 

Calcium is the most abundant body constituent (approx. 2% of body weight). It controls excitability of nerves and muscles and regulates permeability of cell membranes. It act as intracellular messenger for hormones and autacoids and help in coagulation of blood. 

In ihe mammalian body, calcium is required to insure the integrity and permeability of cell membranes. 10 regulate nerve and muscle excitubiliiy. to help maintain normal muscular contraction, and to assure cardiac rhvthmicity. Calcium plays an essential role in several of ihe enzymatic steps involved in blood coagulation and also activates certain other enzyme-catalyzed reactions not involved in any of ihe foregoing processes. Calcium is ihe niosi important element of bone sail. Together with phosphate and carbonate, calcium confers on bone most of its mechanical and structural properties. 

Tanner [49] measured diffusion coefficients of water in three different types of frog muscle cells. He used a variety of magnetic field gradient techniques so as to cover a wide range of diffusion times A= 1 ms to 1 s. The time dependence of the diffusion coefficient was analyzed to obtain the intracellular diffusion coefficients and estimates of the permeability of the cell membranes. In restricted diffusion studies three 90 degree r.f. pulse sequences (stimulated echo) are often used which provides PG-NMR experiments with long diffusion times to explore the dependence of diffusion time on the echo attenuation [49]. 

Calcium ions are essential in a variety of physiological processes including blood clotting, release of neurotransmitter at the synapse, cell division, cell adhesion, secretion, bioluminescence, membrane permeability, muscle contraction, and bio-mineralization35,174 176. In most of these systems, the disposition and functions of membrane proteins are a key in transport and regulation of calcium. Thus in order to understand the functionality of calcium one should look at a membrane system where the biochemical interplay of calcium is known in detail. 

Perhaps the most well-known example is the acetylcholine receptor located on the postsynaptic membrane of the neuromuscular junction49 56 (Fig. 4-1). When bound by acetylcholine molecules, the receptor activates and opens a pore through the cell membrane, thereby increasing the permeability of the muscle cell to sodium.38 56 This action results in depolarization and excitation of the cell because of sodium influx. Another important example of a receptor-ion channel system is the gamma-aminobutyric acid (GABA)-benzodiazepine-chloride ion channel complex found on neuronal membranes in the central nervous sys-... 

Phase 0. Rapid depolarization occurs because of the sudden influx of sodium ions into the cell. At some threshold level, the cell membrane suddenly becomes permeable to sodium ions because of the opening of sodium channels or gates, similar to the spike seen in skeletal muscle depolarization. 

Ivermectin binds to chloride ion channels in parasitic nerve and muscle cells, thereby increasing membrane permeability to chloride. Increased intracellular chloride results in hyperpolarization of nerve and muscle tissues, which results in paralysis and death of the parasite. Ivermectin is well tolerated during shortterm use in mild-to-moderate infections. Administration in more severe infections may cause swollen or tender lymph glands, fever, skin rash, itching, and joint and muscle pain, but these reactions may be... 

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