Calcium-and voltage-dependent dual gating ANO1 is an intrinsic determinant of repolarization in rod bipolar cells of the mouse retina

TMEM16A/anoctamin1 (ANO1), a calcium (Ca²⁺)-activated chloride (Cl⁻) channel, has many functions in various excitable cells and modulates excitability in both Ca²⁺-and voltage-gating modes. However, its gating characteristics and role in primary neural cells remain unclear. Here, we characterized its Ca²⁺-and voltage-dependent components in rod bipolar cells using dissociated and slice preparations of the mouse retina. The I-V curves of Ca²⁺-dependent ANO1 tail current and voltage-gated Ca²⁺ channel (VGCC) are similar; as ANO1 is blocked by VGCC inhibitors, ANO1 may be gated by Ca²⁺ influx through VGCC. The voltage-dependent component of ANO1 has outward rectifying and sustained characteristics and is clearly isolated by the inhibitory effect of Cl-reduction and T16Ainh-A01, a selective ANO1 inhibitor, in high EGTA, a Ca²⁺ chelator. The voltage-dependent component disappears due to VGCC inhibition, suggesting that Ca²⁺ is the essential trigger for ANO1. In perforated current-clamping method, the application of T16Ainh-A01 and reduction of Cl⁻ extended excitation periods in rod bipolar cells, revealing that ANO1 induces repolarization during excitation. Overall, ANO1 opens by VGCC activation during physiological excitation of the rod bipolar cell and has a voltage-dependent component. These two gating-modes concurrently provide the intrinsic characteristics of the membrane potential in rod bipolar cells.