Model number

Model of transmembrane voltage as concentration changes across a membrane with a single channel having a constant conductance.


 Provides current voltage relationships for potassium currents
 through an inflow ion-selective channel conductance. Allows changing of
 concentrations and temperature in order to explore the Nernst relationships.

 Display is set up using log scaling on bottom two panels. Set 'rateo' 
 to a negative rate such as -1 mv/ms to show that Nernst changes at a slow rate.
 Model for monovalent cation in water driven by electrochem gradient.
 Membrane separates 2 regions of fixed concentrations, Iono and Ioni.
 Solute activities are unity. Currents reach S.S. instantaneously.

 The Nernst potential is independent of the conductance. Given a
 single channel conductance about 300 pSiemens; 10^6 chan -> 300 uS.
 What would be the current flow at the starting concentrations 5 and 150 mM?
 Insert suitable concentrations for Ca, e.g. 1e-4 and 2 mM, and for Va, 12 and 144 mM
 and determine the slopes. Adjust valence for each.
 See Notes within this .proj file for guidance.


fig 1

Figure: Transmembrane potential (VIon) calculated using the Nernst equation as a function of inside ion concentration. Inside ion concentration is falling at a constant rate of 1 mM/sec while the outside ion conc remains constant.


The equations for this model may be viewed by running the JSim model applet and clicking on the Source tab at the bottom left of JSim's Run Time graphical user interface. The equations are written in JSim's Mathematical Modeling Language (MML). See the Introduction to MML and the MML Reference Manual. Additional documentation for MML can be found by using the search option at the Physiome home page.

Download JSim model project file

Help running a JSim model.

 Hille B., Ion Channels of Excitable Membranes, Third Edition.
 Sunderland, Massachusetts: Sinauer Associates, 2001, 814 pp. page 19, Figure 1.6

  Vboltzmann, VboltzmannLagged, Goldman, Goldman+pump, HodgkinHuxley
Key terms
Nernst potential
ionic current
gating current
conformational state

Please cite in any publication for which this software is used and send one reprint to the address given below:
The National Simulation Resource, Director J. B. Bassingthwaighte, Department of Bioengineering, University of Washington, Seattle WA 98195-5061.

Model development and archiving support at provided by the following grants: NIH U01HL122199 Analyzing the Cardiac Power Grid, 09/15/2015 - 05/31/2020, NIH/NIBIB BE08407 Software Integration, JSim and SBW 6/1/09-5/31/13; NIH/NHLBI T15 HL88516-01 Modeling for Heart, Lung and Blood: From Cell to Organ, 4/1/07-3/31/11; NSF BES-0506477 Adaptive Multi-Scale Model Simulation, 8/15/05-7/31/08; NIH/NHLBI R01 HL073598 Core 3: 3D Imaging and Computer Modeling of the Respiratory Tract, 9/1/04-8/31/09; as well as prior support from NIH/NCRR P41 RR01243 Simulation Resource in Circulatory Mass Transport and Exchange, 12/1/1980-11/30/01 and NIH/NIBIB R01 EB001973 JSim: A Simulation Analysis Platform, 3/1/02-2/28/07.