Figure 1.

Light-induced tail currents in Drosophila photoreceptors. (A) Whole-cell voltage-clamped recording from WT photoreceptor at −70 mV to bright flashes (5 ms, ∼17,500 effective photons; arrow) in the presence (gray trace) and absence (black trace) of 100 μM ouabain in normal bath (1.5 mM Ca²⁺). A small, slow, outward aftercurrent (maximally ∼30 pA) due to electrogenic Na⁺/K⁺ ATPase, was eliminated by ouabain. Inset: scaled to show entire response. (B) Measurement of the Na⁺/Ca²⁺ exchange tail current in presence of ouabain (recording from the trpl mutant). The onset of the tail current is masked by the much larger LIC; this hidden component was estimated by extrapolating an exponential back to the time of the peak response and the charge integral measured (shaded area). (C) Responses to flashes containing ∼17,500 photons in WT and calx mutants in the presence of ouabain. The conspicuous tail current was absent in calx mutants.