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Thrombin-induced membrane currents in native Xenopus follicles
Q T Nguyen1, J Stinnakre, R Miledi
1Department of Psychobiology, U.C.I. 92715, USA.
Abstract:
The presence and properties of thrombin receptors have been investigated in Xenopus Laevis follicles. In follicles, voltage-clamped at -60 mV or -80 mV, sub-micromolar concentrations of thrombin (Thr) induce smooth inward currents carried by chloride ions, which desensitize over tens of minutes. This desensitization is prevented by PKC inhibitors (staurosporine and H7). Responses are inhibited by hirudin. Inconsistent responses can be observed in defolliculated oocytes. Thr responses, readily recorded in hypo-osmotic solution are abolished by perfusion of normal frog "Ringer" or by the addition of 50 mM sucrose. Thus Thr acts on receptors present in the follicular cells triggering the opening of chloride channels by acting on receptors, likely to be located on follicular cells, via a PKC-regulated pathway.
Insights
Thrombin receptors in Xenopus Laevis follicles trigger chloride channel opening via a PKC-regulated pathway. These receptors, located on follicular cells, mediate thrombin-induced currents that desensitize over time.
Area of Science:
- Reproductive Biology
- Cellular Physiology
- Molecular Pharmacology
Background:
- Thrombin plays a role in various physiological processes, including oocyte maturation.
- The specific mechanisms and cellular localization of thrombin receptors in Xenopus Laevis follicles remain incompletely understood.
Purpose of the Study:
- To investigate the presence and functional properties of thrombin receptors in Xenopus Laevis follicles.
- To elucidate the signaling pathway involved in thrombin-induced responses in these cells.
Main Methods:
- Electrophysiological recordings (voltage-clamp) were performed on Xenopus Laevis follicles.
- Sub-micromolar concentrations of thrombin were applied to induce currents.
- Protein kinase C (PKC) inhibitors (staurosporine, H7) and hirudin were used to probe the signaling pathway.
- Responses were examined under varying osmotic conditions and in defolliculated oocytes.
Main Results:
- Thrombin induced inward chloride currents in Xenopus Laevis follicles voltage-clamped at -60 mV or -80 mV.
- These currents exhibited desensitization over tens of minutes.
- Desensitization was blocked by PKC inhibitors.
- Thrombin responses were inhibited by hirudin, suggesting a specific interaction.
- Responses were observed in intact follicles but were inconsistent in defolliculated oocytes, indicating the involvement of follicular cells.
- Thrombin-induced currents were dependent on osmotic conditions and abolished in normal Ringer solution or with sucrose addition.
Conclusions:
- Thrombin acts on receptors located on Xenopus Laevis follicular cells.
- These receptors trigger chloride channel opening via a pathway regulated by Protein Kinase C (PKC).
- The findings highlight the role of follicular cells in mediating thrombin signaling during oocyte development.