This is a Montecarlo simulation program with a plasma membrane that has an embedded channel separating two compartments named OUTSIDE and INSIDE.
Each compartment contains a solute represented as open circles (O= neutral or O=cation and O=anion ), that may be at different concentrations on each side. Concentration values may be changed by the user by typing values in the Cout= and Cin= windows, when the simulation is NOT running.
The simulation is done by random walk of the molecules or ions in the compartments. The solute may be allowed to cross the channel when it is open. The channel state (open channel or close channel) is controlled by the user.
The solute can be neutral (Click for Neutral) or charged (Click for ions). This is also controlled by the user. When the solute is charged (monovalent ions), the channel is selective to cations (depicted as O, blue), thus excluding anions (depicted as O, red).
The channel crossing produces solute fluxes that are named influx (from outside to inside) and outflux (from inside to outside). The fluxes are proportional to the hits of the molecules to the channel mouth. Because the ions are charged in the ionic case, the crossing is also affected by the electric field induced by the charge separation (depicted as filled circles), as a cation moves from one side to the other. In the steady state, the net flux becomes zero and a membrane potential (Vm=Voltage inside - Voltage outside) is automatically generated, which corresponds to the Nernst Potential. (For a fast view of how that occurs, look at the animation "Origin of the Nernst Potential").
The fluxes only affect concentrations when the volume of the compartments is finite. Finite volume can be selected by the user for the case with neutral molecules (Restore Container). Infinite volume is selected by Remove Container.
Simulation is initiated by START and terminated by STOP. The simulation may be interrupted by freeze and continued by resume. Results are plotted during the simulation on "Plot of fluxes, Voltage and Concentrations", a draggable window (to the right of the container) and they are stored in a "TABLE OF RESULTS", another draggable window, below the containers, after STOP is hit.
ORIGIN OF NERNST POTENTIAL is an animation that depicts the charge separation that originates the membrane potential in a membrane with a cation selective channel.