Membrane Potential

voltage difference measurable at the membrane of living cells between inside and outside the cell, the rest potential is 50 - 100 mV (negative inside) depending on cell type. The M. is based on the unequal distribution of electrolyte ions and proteins on both sides of the membrane. It is caused by the low permeability of the predominantly extracellular sodium ions under resting conditions, by the constant outward transport of Na+ and inward transport of K+, as well as by the very low permeability of the cell membrane for the intracellular proteins and organic phosphate compounds. In total, the intracellular K+ concentration is 35 times higher and the Na+ concentration 20 times lower than in the extracellular space.