Potassium transport through cell membranes

Numerous investigations on the transport of the lithium ion through cell membranes of erythrocytes have established five different pathways by which anion exchange and sodium-potassium co-transport control lithium uptake into the cell, whilst... 

The striking compartmentalization of potassium in intracellular fluid, and of sodium in extracellular fluid, is a condition which is established and maintained by active transport across all plasma membranes. In the absence of active transport pumps, cotransporters and conductance channels, a directional, selective, rapid and regulated movement of potassium (or sodium) through the cell membranes would be impossible. The major molecular pathways of potassium permeation through plasma membranes are Na, K- ATPase, H-K-ATPase, Na-2C1-K-transporter, and potassium conductance channels (Peterson 1997). 

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 transport of hydrated sodium and potassium ions through the cell membrane is slow, and this transport requires an expenditure of energy by the cell. 

Monensin belongs to the family of polyether ionophores. These compounds consist of a series of tetrahydrofuran and tetrahydro-pyran rings and have a carboxyl group that forms neutral salts with alkali metal cations. Their three-dimensional structure presents a lipophilic hydrocarbon exterior with the cation encircled in the oxygen-rich interior. They probably act by transporting cations through the lipid bi-layer of cell membranes, thereby preventing the concentration of potassium by the cells. Evidence for this is... 

There is reason to beheve that cardiac glycosides, like other inotropic substances, act on the contractibility of the heart by affecting the process of calcium ion transfer through the membrane of myocardiocytes. The effect of cellular membranes in electric conductivity is mediated by transport of sodium, calcium, and potassium ions, which is a result of indirect inhibitor action on the (Na+-K+) ATPase of cell membranes. 

Inorganic ions, such as sodium and potassium, move through the cell membrane by active transport. Unlike diffusion, energy is required for active transport as the chemical is moving from a lower concentration to a higher one. One example is the sodium-potassium ATPase pump, which transports sodium [Na ] ions out of the cell and potassium [K ] into the cell. 

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