Figure 3.

T-type voltage-gated Ca²⁺ currents in OffT RGCs are not necessary for light-evoked bursts of APs. A₁, Currents elicited by hyperpolarizing voltage steps (to values between −70 and −100 mV) in OffT RGCs from WT mice. Inset, Voltage dependence and Ni²⁺ sensitivity of inward current following voltage steps in OffT RGCs. The inward current was reversibly inhibited by low concentrations of Ni²⁺ (50 μm; n = 3 cells with >50% recovery after wash). A₂, Flash-evoked change in membrane potential of OffT RGCs under control conditions (solid line) and in the presence of mibefradil (dashed line); the flash strength in both cases was ∼0.1 Rh*/rod. Mibefradil did not significantly effect the light-evoked hyperpolarization (inset, left columns) but abolished the subsequent depolarization (inset, right columns); the Na⁺ channel antagonist QX-314 (1 mm) was present in the internal solution under both conditions. B₁, Currents elicited by hyperpolarizing voltage steps in OffT RGCs from mice lacking Ca_V3.1. B₂, Light-evoked changes in the rate of AP generation, and subthreshold membrane potential trajectory (inset), of an OffT RGC from a Ca_V3.1^−/− mouse. Flash time in panels A₂ and B₂ indicated by arrow.