On the three visual pigments in the retina of the firefly squid, Watasenia scintillans

Abstract

The deep-sea bioluminescent squid, Watasenia scintillans, has three visual pigments: The major one (A1 pigment) is based on retinal and has λmax = 484 nm, the second one (A2 pigment) is based on 3-dehydroretinal and has λmax = 500 nm, and the third one (A4 pigment) is based on 4-hydroxyretinal and has λmax = 470 nm. The distribution of these 3 visual pigments in the retina was studied by HPLC analysis of the retinals in retina slices obtained by microdissection. It was found that A1 pigment was not located in the specific region of the ventral retina receiving the down-welling light which contains very long photoreceptor cells, forming two strata. A2 and A4 pigment were found exclusively in the proximal pinkish stratum and in the distal yellowish stratum. The role of these pigments in the retina is hypothesized to involve spectral discrimination. The extraction and analysis of retinoids to determine the origin of 3-dehydroretinal and 4-hydroxyretinal in the mature squid showed only a trace amount of 4-hydroxyretinol in the eggs. Similar analysis of other cephalopods collected near Japan showed the absence of A2 or A4 pigment in their eyes.