Figure 1.

General features of isolated photoreceptors. A) Isolated ommatidia of Periplaneta americana. Single photoreceptors cluster with their fused rhabdom concentrically around the longitudinal axis of the ommatidium. The rhabdom can be recognized as a dark central structure. Lenses at the distal end (top) and axons at the proximal end (bottom) are ripped off during isolation. Note the pigmentation of the ommatidia. B) Whole-cell capacitances of green-sensitive photoreceptor cells (n = 45). C) Current responses to 1 ms dim light flash stimuli containing less than 1 photon on average showed both single photon absorptions (+) and failures (-). The variability of response latency and amplitude reflects the random properties of phototransduction. The holding potential in voltage clamp mode was -77 mV. D) Voltage responses (top) and corresponding light-induced-currents (middle) to a 10 s long naturalistic light intensity series (bottom) recorded in whole-cell patch clamp. Relative intensities were 1 (gray traces) and 10 (black trace). E) In whole-cell current clamp recordings, voltage responses (top) to current injections (bottom) exhibited both inward- and outward rectification, indicating the presence of voltage-dependent conductances. The small-amplitude depolarizations are single photon responses to ambient light.