Gastrointestinal smooth muscle experiments

MONASH University 

 Medicine, Nursing and Health Sciences
BackgroundExperimental setupSimulationInterpretation
Instructions Experiment Analysis

How to measure changes in ileum contraction

Mobile Support Warning

This simulation was designed with a desktop interface in mind, and may not function correctly on smaller screens or mobile devices.

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!).

Practice calculation of percent change

5mV - 20mV


20mV

 × 100%

Therefore, NA led to a 75% decrease in contraction amplitude.

30mV - 20mV


20mV

 × 100%

Therefore, ACh led to a 50% increase in contraction amplitude.

Virtual experiment

Mobile Support Warning

This simulation was designed with a desktop interface in mind, and may not function correctly on smaller screens or mobile devices.

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 manipulation you wish to perform (nerve stimulation or addition of noradrenaline or acetylcholine to the saline bath).
  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.

Changes in contraction amplitude:  bath + .

Percent change = 

mV − spontAmp


 x 100% = %

Analysis of results

Mobile Support Warning

This simulation was designed with a desktop interface in mind, and may not function correctly on smaller screens or mobile devices.

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

Saline Phentolamine Atropine
Nerve stimulation
Noradrenaline
Acetylcholine

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

Download your data

Quiz: respond based on the table above

Which agonist had the same effect on the contraction amplitude (i.e. increase or decrease) as nerve stimulation?

Which antagonist was more effective in blocking the effect of nerve stimulation on the contraction amplitude?

What kind of nerves were most likely activated by the nerve stimulation?

© 2023 Faculty of Medicine, Nursing and Health Sciences, Monash University
Developed by Glitch Taylor and Dr. Maria del Mar Quiroga, under the direction of Prof. Ramesh Rajan
All queries should be directed to physiol-sim@monash.edu