Chapter 5 - Resting electric potential and ionic currents in the cell

Abstract

In the living organism, diffusion of ions through ion channels or tissue fibers causes electric potential and ionic currents. In equilibrium at rest, the current of each kind of permeable ion is assumed to be not zero but constant while the total sum of current density associated with all permeable ions is zero, and the resting membrane potential is constant. Along with the continuous actions of Na+-K+ ATPase, the membrane that is impermeable to Na+ and permeable to K+ at a resting state maintains the resting potential. The leak ion channels have their own selective filter. The difference of the membrane permeability among different kinds of ions is explained by the number of each kind of leak channel. The ratio of the number of leak channels for K+, Na+, and Cl− is 1.00:0.04:0.45 at a resting state. The Goldman equation is derived by taking account of the membrane permeability for each kind of ion. The resting membrane potential is calculated based on the concentration differences of potassium, sodium, and chloride ions across the membrane and the membrane permeability for each kind of ion. Besides resting membrane potential, there is a calcium oscillation in the cell. The release of stored Ca2+ from the SR or the ER is thought to be the source of oscillation in both excitable and nonexcitable tissue cells.