In this experiment, contractions of the earthworm gut are measured in an organ bath with a force transducer. The effect of neurotransmitters and ionic concentrations on contraction strength and rate will be investigated.
Written by staff of ADInstruments
With acknowledgement to: Dr. Stuart I. Cromarty, Department of Natural Sciences, Assumption College, Worcester, MA, USA. [pic]
Smooth muscle is one of three muscle fiber types found in animals. Unlike skeletal and cardiac muscle cells, smooth muscle cells are not striated, and have single nuclei. Smooth muscles are typically under control of the autonomic nervous system, and do not contract voluntarily. Smooth muscle contracts slowly, and does not exhibit the characteristic “twitch” seen in skeletal muscle. In addition, smooth muscle is not prone to muscle fatigue, making it an ideal component of sphincter muscles. Smooth muscle is found in the gastrointestinal tract of many animals, and is responsible for peristaltic movements. Smooth muscle is also present in the walls of arteries and arterioles, where it helps to regulate blood pressure and flow.
Smooth muscle contractions are affected by calcium and potassium ions. Calcium ion influx into the smooth muscle cell initiates a contraction. Potassium ion concentration in the extracellular medium affects the resting membrane potential of the cell, bringing it closer to or farther away from its threshold voltage. Neurotransmitters affect different types of smooth muscle differently, depending on the association of the smooth muscle with excitable cells. In general, acetylcholine increases the muscle cell’s permeability to calcium, while epinephrine decreases the cell’s permeability to calcium.
The earthworm (Lumbricus spp.) gut can be dissected and examined in vitro using an organ bath and force transducer. This preparation is robust; it can remain active for several hours. In this experiment, you will measure the rate and force of contractions in the in vitro earthworm gut, and examine its response to changes in extracellular ion concentration and to the presence of neurotransmitters.
A computer system
Chart 5.0 or later
Ring stand with micropositioner and clamps
250 ml beaker
Glass finger bowl
Dissection tray with wax or pad
Earthworm saline solution of the following types:
“Normal” saline (room temperature)
Cold saline (5-10°C)
Warm saline (37°C)
A. Set up and calibration of equipment
1. Securely mount the organ bath, micropositioner, and force transducer to the ring stand. The force transducer should be mounted so that it is over the opening of the organ chamber. Close the drain valve on the bottom of the organ bath.
2. Turn on the PowerLab and make sure the USB cable is connected to your computer.
3. Make sure the Bridge Pod is connected to the Pod Port on Input 1 of the PowerLab.
4. Connect the force transducer cable to the back of the Bridge Pod.
5. Launch Chart and open the settings file for this experiment “EW Gut Settings”.
6. A new blank data file will open after a few moments. This file should have one channel, labeled “Force”.
7. Click the Force channel function pop-up menu and select “Bridge Pod”. The Bridge Pod dialog box will open.
8. Observe the signal in the dialog box. Zero this signal by turning the knob on the front of the Bridge Pod (figure). If you cannot zero the Bridge Pod, contact your instructor for assistance.
B. Earthworm dissection
Refer to the diagrams in your earthworm dissection guide for assistance.
1. Fill a fingerbowl halfway with 15% ethanol.
2. Obtain a large...