E-Vector and wavelength discrimination by retinular cells of the crayfish Procambarus
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- Waterman, T.H. & Fernández, H.R. Z. Vergl. Physiol. (1970) 68: 154. doi:10.1007/BF00297692
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Receptor potentials have been recorded intracellularly from single retinular cells in the anterior and dorsal quadrants of the compound eye of the crayfish Procambarus (Fig. 1) stimulated with equal quantum flashes of linearly polarized monochromatic light. Comparisons between two orthogonal stimulus e-vectors respectively parallel and perpendicular to the microvilli of each receptor cell's rhabdomere were made sequentially in about one minute's running time at 20 nm intervals between 400 and 740 nm (Fig. 2).
Of the 91 cells studied 17 responded maximally in the violet (av. λmax= 440 nm) whereas the other 74 cells were most responsive in the yellow-orange (av.λmax=594 nm) (Table 1). For the latter group the λmax of individual cells ranged widely from 538 to 634 nm (Fig. 4). Violet sensitive cells were found only in the anterior quadrant of the eye.
For 29 cells spectral sensitivity curves were plotted from the spectral efficiency curves using response-energy functions determined at λmax or spectral efficiency curves taken at two or more stimulus energy levels (Figs. 5B, 6B, 7). When the sensitivity curves are normalized the vertical and horizontal e-vector responses are closely similar indicating that dichroism of the visual pigment is undoubtedly responsible for the observed differential sensitivity (Figs. 5C, 6C).
For 51 yellow-orange cells where e-vector comparisons can be made more than half (57%) were more responsive to vertical e-vector (Table 2) corresponding very closely with the estimated percentage of retinular cells with microvilli parallel to the body's dorso-ventral axis (57.2%). In contrast five of the seven violet cells available for this comparison gave stronger responses to horizontal e-vector suggesting they may predominantly be the one asymmetrical cell in each ommatidium. Nevertheless both color discriminating types were found to be present in both e-vector channels.
For the 29 cells for which spectral sensitivity curves can be plotted the average sensitivity ratio for the two polarization planes is 3.1 with a range from 1.2 to 11.9 at λmax. Since dichroic absorption ratios directly measured in crayfish have previously been shown to be about 2, the origin of greater spectral sensitivity ratios in individual retinular cells most likely must depend on other functions than photon absorption by a single rhabdomere.