Pumps sodium-potassium

Fig. 5. Tentative mixed potential model for the sodium-potassium pump in biological membranes the vertical lines symbolyze the surface of the ATP-ase and at the same time the ordinate of the virtual current-voltage curves on either side resulting in different Evans-diagrams. The scale of the absolute potential difference between the ATP-ase and the solution phase is indicated in the upper left comer of the figure. On each side of the enzyme a mixed potential (= circle) between Na+, K+ and also other ions (i.e. Ca2+ ) is established, resulting in a transmembrane potential of around — 60 mV. This number is not essential it is also possible that this value is established by a passive diffusion of mainly K+-ions out of the cell at a different location. This would mean that the electric field across the cell-membranes is not uniformly distributed.

The proposed model for the so-called sodium-potassium pump should be regarded as a first tentative attempt to stimulate the well-informed specialists in that field to investigate the details, i.e., the exact form of the sodium and potassium current-voltage curves at the inner and outer membrane surfaces to demonstrate the excitability (e.g. N, S or Z shaped) connected with changes in the conductance and ion fluxes with this model. To date, the latter is explained by the theory of Hodgkin and Huxley U1) which does not take into account the possibility of solid-state conduction and the fact that a fraction of Na+ in nerves is complexed as indicated by NMR-studies 124). As shown by Iljuschenko and Mirkin 106), the stationary-state approach also considers electron transfer reactions at semiconductors like those of ionselective membranes. It is hoped that this article may facilitate the translation of concepts from the domain of electrodes in corrosion research to membrane research. 

Morth JP, Pedersen BP, Toustrap-Jensen MS, et al (2007) Crystal structure of the sodium potassium pump, Nature 450 1043-1050... 

The ionic composition of the cell is maintained by operation of the sodium-potassium pump, which pumps ions from more dilute to more concentrated solutions the Na ions from the cytoplasm to the solution outside, and the K+ in the opposite... 

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. 

Digitoxin and its derivatives bind to the sodium-potassium pump and prevent it from exchanging sodium and potassium ions. When given in small quantities the result, especially in cardiac tissue, is that calcium ion content will be upset and calcium will be liberated from its stores. The newly available calcium can then interact with cardiac muscle protein to cause contraction. This is a therapeutic effect for those suffering from insufficient heart-pumping action (congestive heart failure or dropsy). The heart is made to contract efficiently and forcefully (inotropic effect). However, you can see that there may be a fine line between a necessary contraction and one which... 

The sodium-potassium pump displays a curious stoichiometry. Three sodium ions are pumped from the inside and two potassium ions from the outside of a cell for each molecule of ATP cleaved. Thus, an excess of positive ions is pumped out with the result that a negative charge develops inside the cell and a positive charge accumulates on the outside. This action of the Na+,... 

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. 

Beginning 15 days out from a show, an athlete should increase salt intake 20-30%. This of course means salt intake was never reduced to begin with. The amount must remain reasonably high and steady each day. This creates an environment in which the body does not have to release Aldosterone. This causes salt to stay in muscle tissue and the subsequent attraction of water stores there. Also, the all important maintaining of the sodium-potassium pump is accommodated as well. (During diet phases, this also reduces catabolism.)... 

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... 

Monti, M., Hedner, P Ikomi-Kumm, J., Valdemarsson, S. (1987). Erythrocyte thermogenesis in hyperthyroid patients Microcalorimetric investigation of sodium/potassium pump and cell metabolism. Metabolism 36, 155-159. 

The state of the sodium channel varies in healthy ventricular cells and those damaged by ischemia. This variability in the state has implications for antiarrhymic therapy with sodium channel blocking agents. In sick or damaged ventricular cells (i.e., from ischemia or blockade of the sodium/potassium-ATPase [sodium/potassium pump]), the resting membrane is more positive than the healthy resting membrane potential (Figure 12.10). 

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

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