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

Description

 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.

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.

Equations

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.