Performance of blue- and green-sensitive photoreceptors of the cricket Gryllus bimaculatus
The compound eye of the cricket Gryllus bimaculatus contains a specialized dorsal rim area (DRA) populated by distinct blue-sensitive photoreceptors responsible for perception of polarized light. The rest of the eye is dominated by green-sensitive photoreceptors. Using patch clamp we studied dissociated ommatidia of nocturnal adults and diurnal eight-instar nymphs with the goals (1) of characterizing the biophysical properties of cricket photoreceptors in general and (2) describing the functionally dissimilar blue- and green-sensitive photoreceptors in terms of voltage-gated channel composition and signal coding. Despite different lifestyles, adult and nymph photoreceptors were indistinguishable. No significant circadian changes were observed in K+ currents. In contrast, prominent differences were seen between blue- and green-sensitive photoreceptors. The former were characterized by relatively low absolute sensitivity, high input resistance, slow quantum bumps with long latencies, small light-induced and K+ currents and low steady-state depolarization. Information rate, a measure of photoreceptor performance calculated from voltage responses to bandwidth-limited white noise-modulated light contrast, was 87 ± 8 bits s−1 in green-sensitive photoreceptors vs. 59 ± 14 bits s−1 in blue-sensitive photoreceptors, implying a limited role of DRA in the perception of visual contrasts. In addition, evidence of electrical coupling between photoreceptors is presented.