Fig. 2. Voltage-clamped responses from dissociated Drosophila melanogaster photoreceptors. (A) Quantum bumps in a vertebrate [top, toad rod, courtesy of Professor T. Lamb; data from (Whitlock and Lamb, 1999)] compared with Drosophila melanogaster (below). Note the different scales; the kinetics of the toad bump is approximately 100 times slower than that of Drosophila melanogaster. (B) Drosophila melanogaster quantum bumps recorded in normal (1.5 mmol l^-1), intermediate (0.1 mmol l^-1) and ‘0’ (<100 nmol l^-1) Ca²⁺. The amplitude is reduced and the kinetics greatly slowed in low external [Ca²⁺]. In intermediate concentrations, a slow rising phase appears to trigger a full-sized bump after a brief delay [adapted from (Henderson et al., 2000)]. (C) Responses to 1 s steps of light of increasing intensity (maximum approximately 50 000 effectively absorbed photons per second); the rapid peak-to-plateau transitions are a direct manifestation of Ca²⁺-dependent light adaptation [adapted from (Raghu et al., 2000a)].

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