Figure 6.

I_SOC arises from activation of the light-sensitive channels. Increasing external [Ca²⁺] inactivated I_SOC in WT photoreceptors. The I–V curves were measured 2–8 min after I_SOC was induced by ryanodine plus caffeine (4 μM ryanodine and 10 mM caffeine), and examples of curves from a single cell are presented. The pipette solution included ions that blocked K⁺ channels. Increasing external Ca²⁺ inactivated the inward current. Current traces were elicited by 500-ms voltage steps (−80 to +100 mV in intervals of 20 mV) in a cell bathed in Ca²⁺-free medium (at a holding potential of −20 mV; 0 Ca²⁺, ○) and 2 min after 1.5 mM Ca²⁺ was added to the bathing solution (1.5 Ca²⁺, •, recorded from the same cell). The graphs are the current–voltage relationships (I–V curves) measured from the peak amplitudes of the presented currents (right traces, n = 4).