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ETB2 receptor subtype stimulation relaxes the iris sphincter muscle
A Rocha-Sousa1, J Saraiva, M Amaral
1A. Rocha-Sousa, Department of Physiology, Faculty of Medicine, Porto, Portugal. arsousa@med.up.pt
Physiological Research
|December 20, 2008
Summary
Endothelin B (ET(B)) receptor stimulation causes relaxation in rabbit iris sphincter muscles. This effect is mediated by the ET(B2) receptor subtype, involving nitric oxide (NO) and prostaglandin release.
Area of Science:
- Pharmacology
- Physiology
- Ocular Biology
Background:
- Endothelin B (ET(B)) receptors play a role in various physiological processes.
- Their function in the iris sphincter muscle, particularly concerning smooth muscle relaxation, requires further elucidation.
- Understanding these pathways is crucial for potential therapeutic interventions in ocular conditions.
Purpose of the Study:
- To investigate the effects of ET(B) receptor stimulation on carbachol-precontracted rabbit iris sphincter muscles.
- To identify the specific ET(B) receptor subtype (ET(B1) or ET(B2)) involved in mediating these effects.
- To explore the subcellular pathways, including nitric oxide (NO) and prostaglandins, responsible for the observed muscle response.
Main Methods:
- Experiments were conducted on isolated rabbit iris sphincter muscles (n=51).
- Muscle strips were pre-contracted with carbachol and then exposed to various agonists and antagonists, including sarafotoxin (SRTX-c), endothelin-1 (ET-1), IRL-1620, BQ-788 (ET(B2) antagonist), L-NA (NOS inhibitor), and indomethacin (cyclooxygenase inhibitor).
- Electric field stimulation (EFS) was used to assess contractile responses.
Main Results:
- ET(B) receptor stimulation with SRTX-c and ET-1 (in the presence of an ET(A) antagonist) induced concentration-dependent relaxation of the iris sphincter muscle (10.8% and 9.4%, respectively).
- This relaxation effect was significantly inhibited by the ET(B2) receptor antagonist BQ-788, the nitric oxide synthase (NOS) inhibitor L-NA, and the cyclooxygenase inhibitor indomethacin.
- Selective ET(B1) receptor stimulation with IRL-1620 did not produce a significant relaxation response, and SRTX-c did not alter EFS-induced contraction.
Conclusions:
- ET(B) receptor stimulation effectively relaxes the carbachol-precontracted rabbit iris sphincter muscle.
- The relaxation is primarily mediated through the ET(B2) receptor subtype.
- The underlying mechanisms involve the release of nitric oxide (NO) and prostaglandins.
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