Transporters sodium—potassium pump

Ordinarily, when the current pulse is over, the excess charges will be drained through the passive transport channels, and by operation of the sodium-potassium pumps the original values of membrane potential and of the concentration gradients will be reestablished. However, when in the case of depolarization the negative value of cp has dropped below a certain threshold value, which is about -50 mV, the picture changes drastically Excitation of the membrane occurs. When the current is turned off, the membrane potential not only fails to be restored but continues to... 

A well-known example of active transport is the sodium-potassium pump that maintains the imbalance of Na and ions across cytoplasmic membranes. Flere, the movement of ions is coupled to the hydrolysis of ATP to ADP and phosphate by the ATPase enzyme, liberating three Na+ out of the cell and pumping in two K [21-23]. Bacteria, mitochondria, and chloroplasts have a similar ion-driven uptake mechanism, but it works in reverse. Instead of ATP hydrolysis driving ion transport, H gradients across the membranes generate the synthesis of ATP from ADP and phosphate [24-27]. 

With active transport, energy is expended to move a substance against its concentration gradient from an area of low concentration to an area of high concentration. This process is used to accumulate a substance on one side of the plasma membrane or the other. The most common example of active transport is the sodium-potassium pump that involves the activity of Na+-K+ ATPase, an intrinsic membrane protein. For each ATP molecule hydrolyzed by Na+-K+ ATPase, this pump moves three Na+ ions out of the cell and two K+ ions into it. As will be discussed further in the next chapter, the activity of this pump contributes to the difference in composition of the extracellular and intracellular fluids necessary for nerve and muscle cells to function. 

Palytoxin targets the sodium-potassium pump protein by binding to the molecule in such a way that the molecule is locked in a position where it allows passive transport of both the sodium and potassium ions, thereby destroying the ion gradient that is essential for most cells. 

Reduced salt intake also negatively effects the all important sodium-potassium pump. This is the mechanism the body uses to shuttle many nutrients into cells like those that all muscle fibers are composed of. (Gee, ya think ) This would therefore inhibit creatine and some amino acid structures from adequately transporting, as well as inhibit glycogen synthesis. 

Digitalis exerts its primary effect by inhibiting the sodium-potassium pump on the myocardial cell membrane.66 The sodium-potassium pump is an active transport system that normally... 

Sodium/Potassium pump - ion transport through membranes and ion channels... 

Na+K+ ATPases, so-called sodium-potassium pumps (Figure 4.6), embedded in the basolat-eral membrane. The sodium-potassium pump is a highly conserved integral membrane protein, expressed in virtually all animal cells. The transport of sodium creates both an electrical and a chemical gradient across the plasma membrane. In turn this provides ... 

When an ion is attached to a particular transporter, a similar ion (of the same or a different solute) competing for the same binding site cannot also be bound. For example, the similar monovalent cations K+ and Rb+ appear to bind in a competitive fashion to the same site on a transporter. For some cells, the same carrier might transport Na+ out of the cell and K+ in—such as the sodium-potassium pump alluded to previously. Ca2+ and Sr2+ apparently compete with each other for binding sites on another common carrier. The halides (Cl-, I-, and Br-) may also be transported by a single carrier. 

Alternatively, A and B may refer to the concentrations of an ion or molecule on the outside and inside of a cell, as in the active transport of a nutrient. The active transport of Na+ and K+ across membranes is driven by the phosphorylation of the sodium-potassium pump by ATP and its subsequent dephosphorylation (Section 13.2.1). 

Cystic fibrosis—a fatal, hereditary disease characterized by a heavy mucus buildup in the lungs—is caused by a defective plasma membrane protein. In persons with cystic fibrosis this transport protein, known as the sodium-potassium pump, abnormally transports sodium ions across the membrane without carrying the chloride ions that usually accompany them. Research is currently underway to correct through genetic engineering the faulty gene that codes for the plasma membrane protein. 

Sodium-potassium pump— A special transport protein in the membrane of cells that moves sodium ions out and potassium ions into the cell against their concentration gradients. 

The transport of food into cells involves the action of the sodium-potassium pump and coupled channels. 

Pumps are proteins that can transport ions against electrochemical potential gradients using adenosine-5-triphosphate (ATP) as an energy source. Sodium-potassium pumps maintain intracellular sodium and potassium concentrations in animal cells and also control salt and water absorption by the epithelial cells in the intestine and kidney. The sodium-potassium pump transports three sodium ions out of the cell and two potassium ions into the cell at the cost of one molecule of ATP. The 3 2 coupling ratio results in net loss of sodium ions into the cell down an electrochemical gradient and maintains cell volume. Currently, considerable research is attempting to elucidate the structures of the various isoforms and subunits of sodium potassium pumps. 

The sodium-potassium pump, which exchanges sodium (Na+) for potassium (K+) across the plasma membrane of animal cells, is an example of the active transport mechanism. 

Fig. 2 The red blood cell has played a special role in the development of mathematical models of metabolism given its relative simplicity and the detailed knowledge about its molecular components. The model comprises 44 enzymatic reactions and membrane transport systems and 34 metabolites and ions. The model includes glycolysis, the Rapaport-Leubering shunt, the pentose phosphate pathway, nucleotide metabolism reactions, the sodium/potassium pump, and other membrane transport processes. Analysis of the dynamic model using phase planes, temporal decomposition, and statistical analysis shows that hRBC metabolism is characterized by the formation of pseudoequilibrium concentration states pools or aggregates of concentration variables. (From Ref...

In vitro experiments have shown that vanadium as vanadate inhibits sodium-potassium ATPase activity and thus inhibits the sodium potassium pump (Nechay and Saunders 1978). This pump is necessary for proper transport of materials across cell membranes. The kidney (Higashino et al. 

Ion pumps - Directly couple ATP hydrolysis to transport. A well-studied example is the sodium-potassium pump of the plasma membrane (Figure 10.26). Note that in one turn of the multistep cycle, two potassiums are pumped in, three sodiums are pumped out, and one ATP is cleaved. The pump can be blocked by ouabain which, in the heart, stimulates contraction because sodium concentration increases and stimulates the sodium-calcium pump to remove sodium and import calcium. Increasing calcium leads to stronger muscular contraction. 

See also Thermodynamics of Transport Across Membranes, Passive Versus Active Transport, Transport Mechanisms, Sodium-Potassium Pump... 

Because the driving force for diffusion is a concentration gradient, active transport pumps, such as the sodium-potassium pump, create gradients of these two ions that are continually (though slowly) degraded by diffusion. Note in Table 10.6 that sodium and potassium ions do not have facilitated transport systems, so their permeability constants are very low. 

Active transport, on the other hand, couples transport of compounds across the membrane to energetically favorable processes, such as hydrolysis of ATP. Because of the additional energy provided by the coupled process, active transport systems can "pump" molecules against a concentration gradient. Thus, with active transport provided by the sodium-potassium pump, cells can maintain a higher concentration of potassium ions inside of the cell than outside and a higher concentration of sodium ions outside than inside. 

Sodium also plays an important role in nerve impulse generation and transmission. As a part of the sodium-potassium pump, the difference between the potassium and sodium concentrations is maintained through active transport across the cell membrane as needed with the help of adenosine triphosphate (ATP) as an energy source. The flow of sodium and potassium across the cell membrane of electrically charged cells results in depolarization. Thus sodium is important for nerve and muscle function. As such, sodium imbalances can affect cardiac and respiratory muscle function as well as mobility. 

The unequal distribution of sodium in the intracellular and extracellular fluids maintains an electrochemical gradient that is vital to normal functions of the body and is maintained through active transport using the sodium-potassium pump. Since sodium ions are necessary to maintain fluid levels, normal blood pressure, proper nerve impulse conduction, and the passage of nutrients into the cell, maintaining proper sodium balance is critical to life. 

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