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Endogenous angiotensin II receptors in Xenopus oocytes and eggs
H Sakuta1, M Sekiguchi, K Okamoto
1Department of Pharmacology, National Defense Medical College, Saitama, Japan.
Abstract:
Angiotensin II (AII) induced strongly desensitizing oscillatory Cl- inward currents in both follicle-enclosed and collagenase-treated Xenopus oocytes. The AII response was abolished by EGTA and attenuated by pertussis toxin. Treatment of oocytes with collagenase transiently reduced both the ratio of oocytes responsive to AII and the amplitude of AII responses, followed by restoration to original levels in 3-4 days. The response to adrenaline, which is mediated by endogenous beta-adrenoceptors in follicle cells, however, was irreversibly abolished by collagenase treatment. These results suggest that endogenous current-mediating AII receptors in oocytes are coupled with phosphatidylinositol hydrolysis and localized in the oocyte or in a cellular structure distinct from that for endogenous beta-adrenoceptors. Progesterone-matured Xenopus eggs also responded to AII, and this AII-induced depolarization resembled the fertilization potential in the eggs, suggesting a possible role of AII receptors in processes of fertilization or growth of the eggs.
Insights
Angiotensin II (AII) induced oscillatory currents in Xenopus oocytes, suggesting a role for AII receptors in fertilization. These receptors are distinct from beta-adrenoceptors and linked to phosphatidylinositol hydrolysis.
Area of Science:
- Cellular and Molecular Biology
- Reproductive Biology
- Physiology
Background:
- Angiotensin II (AII) is a key regulator of physiological processes.
- Xenopus oocytes are a valuable model for studying ion channel function and signaling pathways.
Purpose of the Study:
- To investigate the effects of Angiotensin II (AII) on Xenopus oocytes.
- To characterize the signaling pathways and localization of AII receptors in oocytes.
- To explore the potential role of AII in oocyte fertilization and development.
Main Methods:
- Xenopus oocytes were treated with Angiotensin II (AII).
- Ionic currents were measured using electrophysiology.
- Oocytes were treated with collagenase, EGTA, and pertussis toxin to probe receptor function and localization.
- Responses to adrenaline were also assessed.
Main Results:
- AII induced oscillatory chloride inward currents in Xenopus oocytes.
- The AII response was dependent on extracellular calcium and pertussis toxin-sensitive G-proteins.
- Collagenase treatment transiently affected AII responses but irreversibly abolished adrenaline responses, indicating distinct receptor localizations.
- AII-induced depolarization in progesterone-matured eggs resembled fertilization potentials.
Conclusions:
- Endogenous AII receptors in Xenopus oocytes are coupled to phosphatidylinositol hydrolysis.
- AII receptors are localized distinctly from beta-adrenoceptors in oocytes.
- AII signaling may play a role in Xenopus egg fertilization and growth.