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Relaxation of smooth muscle
1Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Canadian Journal of Physiology and Pharmacology
|November 1, 1994
Summary
Antigen sensitization in dogs alters bronchial smooth muscle contraction and relaxation, potentially explaining asthma hyperresponsiveness. Impaired muscle relaxation, particularly after short stimulation, is a key finding.
Area of Science:
- Physiology
- Respiratory Medicine
- Smooth Muscle Biology
Background:
- Asthma is characterized by airway hyperresponsiveness.
- Antigen sensitization in dogs alters bronchial smooth muscle contractile properties.
- Impaired muscle relaxation may contribute to high airway resistance in asthma.
Purpose of the Study:
- To evaluate the relaxation process in sensitized bronchial smooth muscle.
- To investigate the role of altered contractile properties in asthma.
- To develop an index of isotonic relaxation (t1/2,CE) for assessing muscle relaxation.
Main Methods:
- Induction of antigen sensitization in dogs.
- Measurement of bronchial smooth muscle contractile properties.
- Evaluation of isotonic relaxation using t1/2,CE after 1s and 10s stimulation.
- Analysis of cross-bridge cycling rate during relaxation.
Main Results:
- Sensitized bronchial smooth muscle showed prolonged relaxation (t1/2,CE) after 1s stimulation compared to controls.
- No significant difference in relaxation time was observed after 10s stimulation.
- Maximum shortening velocity was greater in sensitized muscle at 2s but not 10s.
- An unexpected spontaneous increase in cross-bridge cycling rate occurred during late-phase relaxation in both groups.
Conclusions:
- Sensitization alters both contraction and relaxation of cross-bridges, potentially explaining asthma hyperresponsiveness.
- The cross-bridge cycling rate spontaneously increases during isotonic relaxation, likely due to contractile mechanism reactivation.