Response of equine airway smooth muscle to acetylcholine and electrical stimulation in vitro.

The research examines the reactions of horse airway smooth muscle when exposed to electrical stimulation and acetylcholine in a controlled environment. It found that contractile force in these muscles is dependent on the intensity of electric stimulation and concentration of acetylcholine, being reduced by certain drugs (atropine or tetrodotoxin).

Experiment Setup

• The researchers isolated smooth muscle strips from equine trachea and bronchi, suspending them in specially-prepared tissue baths.
• Through this arrangement, they measured the isometric contractile force, or the muscle contraction force, in response to different simulations.

Electrical Stimulation

• Carefully controlled square-wave electrical stimuli were applied at a range of voltage levels (10, 12, 15, 18, 20, 25 V), frequencies (3, 5, 10, 15, 20, 25, 30 Hz), and pulse durations (0.2, 0.5, 1.0, 1.5, 2.0 ms).
• The results showed a proportional increase in isometric contractile force with increases in these three parameters.
• The peak contractile response was noted at settings of 18 V, 25 Hz, and 0.5 ms.
• Contractile movement was halted by drugs such as atropine and tetrodotoxin, pointing to the role of neurotransmitters from cholinergic nerves in muscle stimulation.

Acetylcholine Stimulation

• A repetition of the experiment, this time with exogenous acetylcholine at concentrations from 10(-9)M to 10(-4)M, yielded similar linkage between its concentration and isometric contractile force.
• The responsive contractile force exhibited a marked difference between tracheal and bronchial smooth muscles.
• The maximum contractile response to the highest electrical stimulus was almost equal to the response to 10(-4)M acetylcholine, 89% of total for tracheal smooth muscle and 68% for bronchial smooth muscle.