TMEM16A Contributes to Calcium-Activated Chloride Currents and Membrane Potential Changes in the Mouse Oocyte

Oscillations in intracellular Ca²⁺ [Ca²⁺]_i are essential for mouse oocyte activation following fertilization. These [Ca²⁺]_i oscillations also induce repetitive hyperpolarizations in the membrane potential (Em). The present study aimed to identify the channels underlying the Em hyperpolarizations. Sulfhydryl reagents such as thimerosal, that oxidize the IP3-R channel, mimic the physiological changes at fertilization by eliciting simultaneous Em changes and [Ca²⁺]_i oscillations. Thimerosal-induced Em and [Ca²⁺]_i changes were prevented by the non-specific Ca²⁺-activated Cl^- channel (CaCC) inhibitors DIDS and NFA, as well as the TMEM16A/Anoctamin 1 CaCC specific inhibitor, T16Ainh-01. The K⁺ channel blocker TEA, and voltage-gated Cl^- channel blocker 9AC failed to inhibit the Em or [Ca²⁺]_i changes. TMEM16A protein was expressed in all stages of mouse preimplantation development, being localized at the plasma membrane in oocytes. Culture of zygotes in the TMEM16A inhibitor prevented development to the blastocyst stage. In summary, we present the first evidence for CaCC channels, namely TMEM16A, being critical for the initiation of Em hyperpolarisations in mouse oocytes.