Spectral absorption and sensitivity measurements in single ommatidia of the green crab,Carcinus

Summary

Rhabdoms of the green crabCarcinus maenas were examined by microspectrophotometry and found to contain a visual pigment with λ_max at 502–506 nm. Upon irradiation, a stable metarhodopsin formed with unchanged λ_max and molar extinction coefficient. In the presence of 5% glutaraldehyde the rhabdoms were photobleached. Partial bleaching experiments indicate that in the rhabdoms studied, only one visual pigment was present, with an absorption spectrum appropriate for a hypothetical rhodopsin from Dartnall's (1953) nomogram.

Retinular (photoreceptor) cells were studied with microelectrodes. They had negative resting potentials of 30–65 mV and responded to light with depolarizing receptor potentials. All cells had maximum sensitivity at ~493 nm, as did the ERG (electroretinogram). Selective adaptation failed to alter the spectral sensitivity functions of single cells or the ERG. If these spectral sensitivity data are pooled with Wald's (1968), the average sensitivity of the dark-adapted eye is accounted for adequately by the pigment of the rhabdom.

The results of this work do not support the hypothesis of Horridge (1967) that each ommatidium ofCarcinus has two color receptors.