MEMOT
“MEMPOT”© – Computer Simulation of Membrane Potential Measurements
INTRODUCTION
“MEMPOT”© is an interactive graphical simulation program that is designed to show how cell membrane potentials are measured with microelectrodes in the laboratory situation. The simulation shows how the membrane potential depends on the external potassium, [K+]o and external sodium, [Na+]o concentrations and the relative permeability of the membrane to these ions. The program simulates membrane potential measurements in any excitable cell permeable to K+ and Na+ ions (e.g., nerve or muscle).
The Mempot shortcut is located in the Physiology folder on the desktop.
EXERCISE 1 – RESTING POTENTIAL MEASUREMENTS
1. From the menu, open the “Resting Potential Experiment”. This exercise illustrates the effect of varying the external potassium concentration, [K+]o on the resting membrane potential.
2. Choose “Start Experiment”. You should obtain measurements of the resting membrane potential in at least 6 different potassium concentrations from 0.5 to150 mmol/l. (0.5, 1.0, 5.0, 10.0, 20.0, 40.0, 100.0 and 150.0).
3. To do this, enter the value (eg 0.5) into the box and click “ok”. Use the arrow keys to sample each of the 5 cells. Put the electrode into the cell, but be careful not to rupture the cell. The membrane potential will appear on the left of the screen (Vm). Sample each of the 5 cells to get an average resting potential (Vav) and an estimate of error (SEM) at each [K]o. Enter this data into Table 1, along with the internal and external cation concentrations.
4. Once a reasonable range of [K+]o has been investigated, click “Finish Experiment” and return to the “Menu”
5. Open “Graph Resting Membrane Potential Results”. This part of the prac requires you to re-enter the data into the program (“Enter/Edit Data”), which will then generate a graph of resting membrane potential against [K+]o.
6. Plot a curve of the relationship between resting membrane potential
INTRODUCTION
“MEMPOT”© is an interactive graphical simulation program that is designed to show how cell membrane potentials are measured with microelectrodes in the laboratory situation. The simulation shows how the membrane potential depends on the external potassium, [K+]o and external sodium, [Na+]o concentrations and the relative permeability of the membrane to these ions. The program simulates membrane potential measurements in any excitable cell permeable to K+ and Na+ ions (e.g., nerve or muscle).
The Mempot shortcut is located in the Physiology folder on the desktop.
EXERCISE 1 – RESTING POTENTIAL MEASUREMENTS
1. From the menu, open the “Resting Potential Experiment”. This exercise illustrates the effect of varying the external potassium concentration, [K+]o on the resting membrane potential.
2. Choose “Start Experiment”. You should obtain measurements of the resting membrane potential in at least 6 different potassium concentrations from 0.5 to150 mmol/l. (0.5, 1.0, 5.0, 10.0, 20.0, 40.0, 100.0 and 150.0).
3. To do this, enter the value (eg 0.5) into the box and click “ok”. Use the arrow keys to sample each of the 5 cells. Put the electrode into the cell, but be careful not to rupture the cell. The membrane potential will appear on the left of the screen (Vm). Sample each of the 5 cells to get an average resting potential (Vav) and an estimate of error (SEM) at each [K]o. Enter this data into Table 1, along with the internal and external cation concentrations.
4. Once a reasonable range of [K+]o has been investigated, click “Finish Experiment” and return to the “Menu”
5. Open “Graph Resting Membrane Potential Results”. This part of the prac requires you to re-enter the data into the program (“Enter/Edit Data”), which will then generate a graph of resting membrane potential against [K+]o.
6. Plot a curve of the relationship between resting membrane potential