The resting resting membrane potential is an electrical potential (reserve) that forms between the outer surface of the cell membrane and the inside of the plasma membrane. The inner side of the membrane relative to the outer surface always has a negative charge. For cells of each species, the resting potential is almost constant. So, in warm-blooded skeletal muscle fibers it is 90 mV, for myocardial cells - 80, nerve cells - 60-70. Membrane potential is present in all living cells.
In accordance with modern theory, the considered electrical reserve is formed as a result of active and passive movement of ions.
Passive movement occurs along the concentration gradient, it does not require energy costs. The resting cell membrane is more permeable to potassium ions. In the cytoplasm of their nerve and muscle cells, they (potassium ions) are present thirty to fifty times more than in the intercellular fluid. In the cytoplasm, ions are in free form and diffuse, in accordance with the concentration gradient, into the extracellular fluid through the membrane. In the intercellular fluid, they are retained by intracellular anions on the outer surface of the membrane.
The intracellular space contains mainly anions of pyruvic, acetic, aspartic and other organic acids. Inorganic acids are contained in relatively small quantities. Anions cannot penetrate the membrane. They remain in the cage. Anions are located on the inner side of the membrane.
Due to the fact that the charge is negative for anions and positive for cations, the outer surface of the membrane has a positive charge, and the inner one is negative.
There are eight to ten times more sodium ions in the extracellular fluid than in the cell. Their permeability is negligible. However, due to the penetration of sodium ions, the membrane potential decreases to some extent. In this case, diffusion of chlorine ions into the cell also takes place. The content of these ions is fifteen to thirty times higher in extracellular fluids. Due to their penetration, the membrane potential increases slightly. In addition, a special molecular mechanism exists in the membrane. It provides active promotion of potassium and sodium ions in the direction of increased concentration. Thus, ionic asymmetry is maintained.
The active movement of ions is the result of the functioning of the potassium-sodium "pump" (pump). Active movement of sodium ions from the cell is due to the penetration of potassium ions into the cell. In a coupled pump, transport is carried by carriers, which, in turn, are transported by metabolic energy during the decay of ATP. Due to the energy of hydrolysis of ATP molecules, 2 potassium ions penetrate into the cell, and 3 sodium ions are transported out.
At rest, up to twenty percent of cellular energy resources are expended in the muscle fibers to ensure the functioning of ion pumps .
Under the influence of the enzyme adenosine triphosphatase, ATP is cleaved. Poisoning of nerve fibers with cyanides, monoiodoacetate, dinitrophenol and other substances, including those that stop the synthesis and glycolysis of ATP, provokes its (ATP) decrease in the cytoplasm and the cessation of the functioning of the "pump".
The membrane is also permeable to chlorine ions (especially in muscle fibers). In cells with high permeability, potassium and chlorine ions equally form a membrane rest. Moreover, in other cells, the contribution of the latter to the indicated process is insignificant.