Influences of External and Internal Ionic Concentrations on the Action Potential

(contributed by Dr. James. Bassingthwaighte)

These may be explored by the user. The file CaoIncr.par is set up to show three situations, namely the shape of the first action potential in a series with Ca_o =2 mM, then 3 mM, and 4 mM. To see how the APs change with time the program should be run to include more beats. For example, under the menu "Parameters" click on "t", and then change the ending time to 5000 ms instead of 1000 ms, (The program is set up to repeat the exciting stimulus once per second.)

Users can change external potassium concentration, K_o, by clicking on the "Ionic Concentrations" button on the model window. To change initial internal ionic levels (K_i, Na_i, or Ca_i), clicking on the "initial Conditions" button. Change values by typing in a new value followed by a carriage return and then hit "Run".

To observe that there is an influence of the Na/Ca exchanger on the action potential change, change the input parameter kNaCa, and Run again. You can set this up in the loops too. To do that, click on the "Model" menu in the control panel, click on "Run config" to open the menu for loop control. There you will see the setup for changing Ca_o with the three levels, 2, 3, and 4 mM with the loops (right upper) set to 3. You may deactivate the Ca_o changes by hitting the "deactivate" button just immediately above "parameter", and then write an analogous command in the empty line below, For example type in under "Parameter" kNaCa, which will cause the value to show up, 0.3 as currently set. Under "Expression" write a list of values you would like to explore, separated by commas. Set the number of Loops (right upper) to match the number of values in your list. Alternatively, type in an expression: e.g. @*0.5, which means take the current value and multiply it by 0.5 in subsequent loops. When you become impatient for a solution to end, hit "Next loop" or "Cancel".