Microspectrophotometric evidence for two photointerconvertible states of visual pigment in the barnacle lateral eye.

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Abstract
Microspectrophotometrically derived difference spectra from the barnacles Balanus amphitrite and B. eburneus show that a blue illumination after an orange illumination causes a decrease in absorption in the blue region and an increase in absorption in the green-yellow region, with an isosbestic point around 535 nm. Orange-following-blue illumination causes the reverse changes. The dark time between adapting and measuring lights has no influence on the data. Results confirm previously reported ERP [early receptor potential] measurements which indicate that the barnacle visual pigment has 2 photointerconvertible dark-stable states. If a Dartnall nomogram shape is assumed for the 2 absorption spectra, a best fit to the observed difference spectra is obtained with nomograms peaking at 492 nm and 532 nm, with a peak absorbance ratio around 1.6:1. These 2 nomograms fit very well the ERP action spectra of metarhodopsin and rhodopsin, respectivley, indicating that ERP is a reliable measure of visual-pigment changes in the barnacle. The existence of a photostable blue pigment is demonstrated in B. eburneus and in some of B. amphitrite receptors; the possible influence of this photostable pigment on the various action spectra measured in the barnacle is discussed.