The membrane potential , also the transmembrane potential or the membrane voltage , sometimes the Nernst potential is the difference in electric potential (electric gradient) that arises between the charges of the inner and outer sides of a semipermeable membrane (in the particular case of a cell membrane). As for the outer surface of the cell, the typical values of the membrane potential for it are in the range from -40 mV to -80 mV.
Content
Physical Basics
Jonah and the Power That Makes Their Movement
Electrical signals that occur inside biological organisms are due to the movement of ions [1] . The most important cations for the action potential are sodium (Na + ) and potassium (K + ) cations [2] . Both of these monovalent cations carry one positive charge. A calcium cation (Ca 2+ ) can also participate in the action potential [3] ; it is a divalent cation that carries a double positive charge. Chlorine anion (Cl - ) plays an important role in the action potentials of some algae [4] , however, only a small part takes part in the action potentials of most animals [5] .
Ion Pumps
An ion pump is a transport system that provides ion transfer with a direct energy expenditure despite concentration and electric gradients [6] .
Ion channels
Ion channels are integral membrane proteins through the pores of which ions can move from the intercellular space into the cells and vice versa. Most ion channels exhibit high specificity (selectivity) with respect to a single ion. For example, most potassium channels are characterized by a high selectivity ratio of potassium cations over sodium cations in a ratio of 1000: 1, although potassium and sodium ions have the same charge and only slightly differ in radius. The channel pore, as a rule, is so small that ions must pass through it in the same order [7] .
Equilibrium potential (Nernst potential) or reverse potential
the equilibrium potential of the ion is the magnitude of the transmembrane voltage at which the diffusion and electric forces are opposed to each other, so that the resulting ion flux through the membrane is zero due to the same flow rate into and out of the cell. This means that the transmembrane voltage precisely counteracts the ion diffusion force, so that the total ion current through the membrane is zero and unchanged. Reversible potential is important because it generates a voltage that acts on the ion channels, making them permeable to ions.
The equilibrium potential of a specific ion is usually denoted by Ei. The potential for any ion can be calculated using the Nernst equation . For example, the reverse potential for potassium ions will look like this:
Where:
- E e, K + is the equilibrium potential of K + ions, measured in volts;
- R is the universal gas constant equal to 8.3144 J / mol * K;
- T is the absolute temperature in kelvins (K);
- z is the number of elementary charges of ions participating in the reaction;
- F is the Faraday constant equal to 96485 Cl / mol;
- [K + ] 1 - extracellular concentration of potassium ions, measured in mmol * l;
- [K + ] 2 - intracellular concentration of potassium ions, measured in mmol * l.
Reversing potential (Eng. Reversal potential) is numerically equal to the equilibrium potential. The term reverse potential reflects the aspect that, when passing through a given value of the membrane potential, the direction of the ion flow reverses.
Rest potential
Graded Values
Other values
Effects and Consequences
Notes
- ↑ Johnston and Wu, p. 9.
- ↑ Bullock , Orkand, and Grinnell, pp. 140–41.
- ↑ Bullock , Orkand, and Grinnell, pp. 153–54.
- ↑ Mummert H., Gradmann D. Action potentials in Acetabularia: measurement and simulation of voltage-gated fluxes (English) // Journal of Membrane Biology : journal. - 1991. - Vol. 124 , no. 3 . - P. 265-273 . - DOI : 10.1007 / BF01994359 . - PMID 1664861 .
- ↑ Schmidt-Nielsen , p. 483.
- ↑ Agadzhanyan N.A., Smirnov V.M. General physiology of excitable tissues; the role of ion pumps in the formation of the resting potential. - 2007. - S. p. 58.
- ↑ Eisenman G. On the elementary atomic origin of equilibrium ionic specificity // Symposium on Membrane Transport and Metabolism. - New York: Academic Press, 1961. - P. 163–79. Eisenman G. Some elementary factors involved in specific ion permeation // Proc. 23rd Int. Congr. Physiol. Sci., Tokyo. - Amsterdam: Excerta Med. Found., 1965. - P. 489-506.
* Diamond JM, Wright EM Biological membranes: the physical basis of ion and nonekectrolyte selectivity (English) // Annual Review of Physiology : journal. - 1969. - Vol. 31 . - P. 581-646 . - DOI : 10.1146 / annurev.ph.31.030169.003053 . - PMID 4885777 .