The membrane potential (MP) is the potential difference between naru w hydrochloric and inner surfaces of the membrane of the excitable cells in its rest conditions. On average, in cells of excitable tissues, MP reaches 50 – 80 mV, with a minus sign inside the cell. Investigation of the nature of the membrane n of the potential of showed that in all excitable cells (neurons, muscle fibers, myocardiocytes, smooth muscle cells) obuslo its presence in Leno predominantly by K + . As is known, in excitable cells due to the work of the Na – K pump, the concentration of K + ions in the cytoplasm, it is maintained at a level of 150 mM at rest, while in the extracellular medium the concentration of this ion usually does not exceed 4–5 mM. This ozn and chaet that the intracellular concentration of K + in 30 – 37 times higher than the corolla th cell. Therefore, according to the concentration gradient, K +ions tend to exit the cell into the extracellular environment. In conditions of rest, indeed, there is a flow of cells leaving the ions K + , and the diffusion axes in fected by potassium channels, most of which is open. The p th result that the excitable cell membrane is impermeable for the internal and cell anions (glutamate, aspartate, organic phosphates) for VNU m renney surface of the cell membrane due to ion yield K + mod and zuetsya excess of negatively charged particles and on the exterior – an excess of positively charged particles. There is a difference of potency and fishing, t. e. membrane potential, which prevents excessive in s course of K + from the cell. At a certain value of the magnetic field , equilibrium occurs between the output of K + ions in the concentration gradient and the input (return) of these ions in the resulting electric gradient. Me m abusive potential at which this equilibrium is reached, received Mr. and title of the equilibrium potential . In addition to K + ions, Na + and C l ions make a certain contribution to the creation of membrane potential . In particular, it is known that the concentration of ions Na + in the extracellular medium 10 times bol s Chez than inside cells (140 mM vs. 14 mM). Therefore, ions of N a + in conv about ditions n about Koya seek to enter the cell. However, most of the sodium channels is closed at rest (relative permeability and a new Na + , with y AH from the experimental data obtained in the squid giant axon, 25 times lower than for the ions K + ). Therefore, the cell Rin of dit only a small flow of ions Na + . But this is enough to at least partially compensate for the excess of anions inside the cell. Center a tion and a new C l – in the extracellular medium is also higher than that inside the cell (125 mM to 9 mM), and therefore these anions also tend to enter the cell, och e seen by chlorine channels.
Thus, major ions determining the value of MP I in lyayutsya ions K + , leaving the cell. Ions Na + , entering into the cell in n th large quantities of partially reduced size IP, and the ions C l – , that to the same members of the cell in conditions of rest, to some extent, the computer n siruyut this influence of ions Na + . Incidentally, in many EXPERIMENTAL n max various excitable cells found that the above pronitsa e bridges of cell membranes for ions of Na + in conditions of rest, the lower the f guise MP. To MP is maintained at a constant uro in not necessary to maintain ionic asymmetry. For this, in particular, serve ion pumps ( Na – K – pump, as well as, probably, C l – pump) which restore ion asymmetry, especially after the act of excitation. Since this type of ion transport is active, t. e. requires energy, then to maintain the membrane potential of the cell requires the constant presence of ATP.