Gastrointestinal smooth muscle experiments

How to measure changes in ileum contraction

The gastrointestinal smooth muscle performs isotonic contractions, meaning that the muscle's length changes, but the tension remains unchanged. In this practical, the bottom end of the ileum section is fixed, and we measure the changes in length by attaching the upper end of the ileum section to a mobile lever via a string. This lever is attached to a transducer, which converts the lever deflections (due to the changes in length of the ileum section) to changes in mV. (NOTE: we use mV only because it makes calibration easier, but you can think of it as a measure of length instead). A very relaxed and extended ileum will mark a low voltage value, whereas a contracted ileum marks a high voltage. When the ileum is at rest performing its baseline contractions, it is at an intermediate state of relaxation/contraction. This is important, because it allows the flexibility of being able to relax more, or contract more, depending on the requirements.

The main objective of this activity is to understand the effects of autonomic nerve activation on the smooth muscle cells of the ileum. There are many ways to measure changes in length with nerve stimulation or under the effects of different drugs, but for this practical we have focused on the contraction amplitude. Although this does not provide an exact measure of length change, it is a good enough approximation, and relatively simple to obtain.

Let's do a practice calculation with the example trace shown below. Once you've completed the practice calculations (i.e. once you've calculated the percentage changes in contraction amplitude for both noradrenaline [NA] and acetylcholine [ACh]) then two new tabs will appear at the top, next to the gray "Instructions" tab: a "Experiment" tab and an "Analysis" tab. Please complete all activities in these two new tabs (this is the fun part!).

Virtual experiment

Please note that in the Experiment tab we will require more precision in the responses. Click on any part of the graph to display the voltage value at that point.

1. Use the drop-down box to choose the solution to go with nerve stimulation (saline or the addition of noradrenaline or acetylcholine).
2. Click the "Start recording" button for the graph to populate. Click on any part of the graph to display the voltage value at that point (for calculation of amplitudes).
3. Fill all input boxes below the graph to collect all the data you need in order to determine the type of nerves you are primarily stimulating.
4. Once you have calculated the percentage change in the contraction amplitude for all three manipulations in the saline bath, add an antagonist (phentolamine or atropine) to the bath by clicking on the corresponding legend entry (in the box to the right of the preparation). Then calculate the effect of all three manipulations again!
5. Keep track of the conditions you have completed by making sure the corresponding value has been transferred to the table in the "Analysis" tab - If it hasn't, make sure you completed all the calculations for that condition! Then the percentage change value will be transferred.

Analysis of results

The following table will populate as you calculate the percent changes for each condition in the "Experiment" tab:

If you have any questions about the table above, please download it and ask your demonstrator!

Download your data