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!).
