Calcium- and Voltage-Dependent Dual Gating ANO1 is an Intrinsic Determinant of Repolarization in Rod Bipolar Cells of the Mouse Retina

Abstract

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.