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Volume-Regulated Anion and Organic Osmolyte Channels in Mouse Zygotes¹

^a Loeb Research Institute and Departments of Obstetrics and Gynecology (Division of Reproductive Medicine), and ^b Cellular and Molecular Medicine, University of Ottawa, and ^c Human IVF Program, Ottawa Hospital, Ottawa, Ontario, Canada K1Y 4E9

Whole-cell currents in mouse zygotes were measured using the patch-clamp technique in whole-cell mode. Upon exposure to hypotonic medium, patch-clamped zygotes increased in volume and developed a large swelling-activated current. The swelling-activated current was blocked by Cl^- channel blockers, and the magnitude of the current and reversal potential were dependent on the Cl^- gradient. Thus, the swelling-activated current had the properties of a current mediated by anion channels. However, in addition to being permeable to Cl^- and I^- (with I^- having the greater permeability), there was also a significant swelling-activated conductance to aspartate and taurine, indicating that the swelling-activated channels in zygotes conduct not only inorganic anions but organic osmolytes as well. This swelling-activated anion and organic osmolyte pathway likely underlies the ability of zygotes to recover from an increase in volume, and it may function to regulate intracellular amino acid concentrations.

¹ This work was supported by a Whitaker Foundation Biomedical Engineering Grant and a Medical Research Council of Canada Operating Grant (MT12040).

² Correspondence: Jay M. Baltz, Loeb Research Institute, 725 Parkdale Ave., Ottawa, ON, Canada K1Y 4E9. FAX: 613 761 5327; jbaltz{at}lri.ca

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