You are given a piece of smooth muscle tissue you stimulate

You are given a piece of smooth muscle tissue, you stimulate it with Norepinephrine and find the muscle responds with contractions. Your hypothesis is that the muscle contraction is caused by the activation of 1 adrenergic receptors. Now you need to design an experiment protocol to test your hypothesis.

Write an experimental protocol to demonstrate your work, for each step in the protocol you write the chemical(s) you add, why you add, what result you are expecting to see e.g. contract, relax, no response. If the step is to wash the tissue with fresh PSS, then you do not need to indicate the responses.

Solution

Answer:

The relaxation and contraction state of the smooth muscle is through ligand gated channels or receptors. This is predominantly modulated by the autonomic nervous system and that is by the neurotransmitter norepinephrine.

Norepinephrine can work on two completely different types of receptors. First, the alpha-1 adrenergic receptors present on the blood vessels and will cause contraction when activated. Second, the beta-2 adrenergic receptors are found in the bronchi of the lungs. The smooth muscle relaxes and does not contract in response to norepinephrine.

The experimental protocol for the above work is as under:

Step 1:

Chemical added: norepinephrine, activates alpha and beta receptors

Response: Blood vessels contract slightly.

Step 2:

Chemical added: PSS

Response: Washing off the norepinephrine brings the blood vessel to its basal state.

Step 3:

Chemical added: Alpha-1 specific antagonist (Doxazosin) and Norepinephrine. It blocks norepinephrine alpha-1 receptors.

Response: The blood vessel should not contract. Instead, it can relax (in lungs) due to the activation of Beta-2 adrenergic receptors.

Step 4:

Chemical added: Wash with PSS. This will remove the antagonist and norepinephrine.

Response: The blood vessel should maintain its basal state.

Step 5:

Chemicals added: Beta-2 specific adrenergic receptor antagonist and norepinephrine. Beta-2 specific adrenergic receptors should be blocked while alpha-1 receptors should respond.

Response: The blood vessel should contract in response to norepinephrine.

Step 6:

Chemicals added: Wash with PSS. The antagonists and norepinephrine should get washed off.

Response: The blood vessel should return to its basal state.

(The agonists, antagonists and PSS can be added through the perfusion system)