Nomograms of the Goldman equation.

Solutions of the Goldman equations for sodium and potassium ions are displayed in nomograms which allow one to determine which values of the variables in the equation (including the activity of the Na/K pump) are compatible with possible steady states of a cell. The nomograms are particularly suited for the study of relative changes of the cell parameters when one or more of them are altered and the cell undergoes a transition from one steady state to another. Special diagrams are presented for finding the changes of the slope conductance (determined at a clamp potential of -80 mV) associated with such transitions. Separate diagrams are given for the cationic component conductance, (gNa + gK), and the anionic component conductance, gCl. The application of the nomograms is illustrated by the exemplary solution of a problem taken from muscle physiology. Further applications of the nomograms are indicated and the limitations of the method are described. The effects of differing activity coefficients in the intra- and extracellular spaces, as well as the contribution of the electrogenic Na/K pump current to the resting potential are discussed.