E1 Resting membrane potential (Nernst/Goldman-Hodgkin-Katz)

Title

The resting membrane potential arises from the unequal partitioning of ions (mainly K+, Na+ and Cl-) between the intracellular and extracellular milieu, sustained by concentration gradients, selective membrane permeabilities and the active transport of the Na+/K+-ATPase pump. For a single ion in electrochemical equilibrium, the potential at which the electric force exactly offsets the diffusive force is given by the Nernst equation, which depends on the valence of the ion, the temperature, and the ratio of concentrations on both sides of the membrane. However, the actual membrane is simultaneously permeable to several ions with different relative permeability, so the observed membrane potential does not coincide with the Nernst potential of any individual ion, but rather results from the Goldman-Hodgkin-Katz (GHK) equation, a permeability-weighted average of the equilibrium potentials of each ionic species. Each individual ionic current can be described ohmicly as the product of the channel conductance times the electrochemical driving force (difference between the membrane potential and the Nernst potential of that ion). At steady state, the sum of all net ionic currents through the membrane is zero, which defines the equilibrium point of the resting potential. The membrane capacitance, together with its total conductance, further determines the time constant with which the membrane potential responds to perturbations. This model constitutes the basis (series E) on which the models of generation and propagation of the action potential (E02, E03) and their associated anomalies (series A) are built.

ID:4259