Advances in Photoreception Proceedings of a Symposium on Frontiers of Visual Science (1990) / Chapter Skim
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Optical and Molecular Design of Rods
Optical and Molecular Design of Rods
Pages 2-16
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showed that the green rod is the short-wavelength receptor for a color opponent process at photopic and mesopic light intensities. In contrast to the thin rods with pooled responses of many species, Jagger (1988)
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Figure 1 is a black and white reproduction of part of Boll's 1877 color plate showing the frog rod mosaic with its pink and green rods after illumination with short-wavelength light. The dark spots are green in the original color plate, and the light spots representing the bleached pink rods are colorless.
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NOTE: Arrow indicates the external limiting membrane been bleached, as shown in Boll's figure. This was confirmed by Liebman and Entine (1968~: It is of some interest that our green rods show no light absorption in the redorange region that would explain results of Denton and Willie who found such absorption in end-on measurements using photographic densitometty (Demon and Wyllie, 1955~.
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The green rod's aperture is its myoid near the external limiting membrane. Light that reaches the outer segment must first pass through the myoid.
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An even smaller diameter myoid, as illustrated in curse d, would tend to cut off much of the light in the visible spectrum. Green Rod Function Green Rods May be Color Receptors If we accept that the green myoid in combination with the outersegment 433-nm pigment can explain the rod's end-on color, that still leaves the problem of its function.
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Using a 5-mm posterior nodal distance (PND) eye as a sample eye size, the green rods by themselves would not be useful for spatial resolution because they could support only a Nyquist frequency of 2 cycles per degree.
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Rods and cones might be expected to have small diameters not only because separate optical channels should be as small as possible, consistent with the diffraction limited image, to maximize resolution but also to facilitate temporal resolution by limiting diffusion transit times. Rod outer segments of many animals ranging from fish to mammals are about 2 Em in diameter.
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1985~. On the other hand, though cyclic GMP increases channel conductance, whether that is because it binds the channel directly is not known, since the patch contains substances other than the ROS plasma membrane (Kolesnikov et al., 1987~.
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The recovery rate of the cyclic GMP responses was more nearly matched to that of the receptor potential. Finally in Figure 4C, in which the light flash was a log unit dimmer than that of Figure 4B, the recovery rate of the receptor potential matches the recovery rate of the cyclic GMP response (and presumably PDE activity)
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(1986) found that cyclic GMP metabolic flux increased about 4.5-fold for a 3-log unit increase in light intensity with little change in measurable cyclic GMP levels.
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We obtained additional support for this hypothesis by testing whether the response to a light flash can recover when PDE activated by the flash is inhibited from deactivation by the introduction of the nonhydrolyzable analog of GTP, guanyl-5'-yl imidodiphosphate, p[NH] ppG, into the outer segment using the whole-cell patch clamp technique (Kondo and Miller, 1988~.
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Light revs up PDE~dase cycle, causing it to race. Light adaptation reduces the ROS inward calcium current and [Caii, which activates g-pyclase to rapidly increase cyclic GMP levels, which truncates response.
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Science 180:1178-1180. Fesenko, E.E., S.S., Kolesnikov, and A.L Lyubarsky 1985 Induction by cyclic GMP of cationic conductance in plasma membrane of retinal rod outer segment.
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Cugnoli 1986 Guanylate cyclase in rod outer segments of the toad retina. FEBS Letters 203:73-76.
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Detwiler 1987 Intracellular biochemical manipulation of phototransduction in detached rod outer segments. Proceedings of the National Academy of Sciences, USA 84:9290-9294.
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