Biological Sciences 300/301, Smith College | Neurophysiology
Checklist for Lab 3: The Effect of Potassium
Concentration on the Resting Potential
http://www.science.smith.edu/departments/NeuroSci/courses/bio330/labs/labcheck3.html
UPDATED: February 2, 2005
1.
Background
for this lab
A. Review the concept of equilibrium potentials, as given by the Nernst equation:
The concept is discussed on the lab Web site and in your textbook.
B. Look at the pop-up photo and diagram to understand the location of the median (inner) deep extensor muscles.
C. Review the function of the voltage follower amplifier and preview the video and still photos of the dissection before coming to lab.
2. Procedures
A. One person from each team should help make crayfish saline mixtures containing different amounts of K+. Three intermediate mixtures are needed in addition to the two stock solutions (high-K 60 mM and normal-K 5.4 mM K+). Each group will use the same five solutions so we can pool data.
B. The other person is responsible for arranging the equipment.
C. When solutions and equipment are ready, snip off a crayfish tail and do the simple dissection.
D. For each solution, starting with the lowest K+ concentration, record the resting potential from four or five different muscle cells by impaling the cells with a microelectrode and writing down the resting potential..
E. Plot the invidual points as you go along, using the graph paper on the back of this page.
3.
Plotting
data
A. Draw a single straight line through your data points. Post your graph on the bulletin board.
B. Answer the question about how to estimate the internal concentration of K+.
C. In a table on the blackboard, write the mean (average) value of your resting potential data for each solution. Consider volunteering to plot the class data using a spreadsheet if you can work out how to have a logarithmic x-axis.