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Changes in cholinergic and adrenergic responses of organ-cultured chick smooth muscle
Abstract:
Chick expansor secundariorum muscles were organ-cultured soon after hatching. Various contraction agonists or other agents were added to the nutrient medium to examine their effects on muscle chemosensitivity. The presence of noradrenaline, acetylcholine or barium chloride in the nutrient medium progressively reduced the maximum acetylcholine contraction, while the maximum noradrenaline contraction remained unaltered as compared to the BaCl2 or KCl contraction. The desensitizing effect of acetylcholine was abolished by adding atropine to the nutrient medium; the effect of noradrenaline was abolished by adding phentolamine or verapamil. Although 40 days are required after hatching for the acetylcholine response of this muscle to disappear in situ, the present findings suggest that already upon hatching, the acetylcholine response is susceptible to disappearance. Furthermore, the mechanism which abolishes the acetylcholine response of this smooth muscle may be closely related to muscle contraction.
Insights
Newly hatched chick smooth muscles show a rapid loss of acetylcholine response, suggesting contraction mechanisms influence chemosensitivity. This contrasts with slower in situ changes, highlighting early developmental plasticity in muscle chemosensitivity.
Area of Science:
- Muscle physiology
- Developmental biology
- Pharmacology
Background:
- The expansor secundariorum muscle in chicks is a model for studying smooth muscle development and chemosensitivity.
- Understanding the factors influencing muscle response to neurotransmitters is crucial for developmental studies.
Purpose of the Study:
- To investigate the effects of various agents on the chemosensitivity of chick expansor secundariorum muscles soon after hatching.
- To explore the mechanisms underlying the potential disappearance of acetylcholine response in developing smooth muscle.
Main Methods:
- Organ culture of chick expansor secundariorum muscles post-hatching.
- Exposure to contraction agonists (noradrenaline, acetylcholine) and other agents (barium chloride, KCl).
- Assessment of maximum contraction responses and desensitization effects.
Main Results:
- Noradrenaline, acetylcholine, and barium chloride progressively reduced maximum acetylcholine contraction.
- Maximum noradrenaline contraction remained unaltered compared to barium chloride or potassium chloride contractions.
- Acetylcholine desensitization was blocked by atropine; noradrenaline desensitization was blocked by phentolamine or verapamil.
Conclusions:
- Chick expansor secundariorum muscles exhibit susceptibility to acetylcholine response loss even upon hatching.
- The mechanism for abolishing the acetylcholine response in this smooth muscle appears closely linked to muscle contraction.
- These findings suggest rapid developmental changes in smooth muscle chemosensitivity shortly after hatching.