Photosensitivity of retinular cells in white-eyed crayfish (Procambarus clarkii)

A B S T R A C T The eyes of crayfish were exposed to lights of known spectral composition, and the course of regeneration was followed in the dark by measuring the content of rhodopsin and metarhodopsin in single rhabdoms isolated at various times after the adaptation, using an assay that is based on the fluorescence of metarhodopsin . Complete recovery requires several days in the dark after intense adaptation to orange light, but requires <2 d after blue light exposure . Following an orange light exposure with blue produces recovery kinetics characteristic of the blue light exposure alone . This quickening of recovery occurs whether the receptors are exposed to blue light either immediately or many hours after the original exposure to orange . Conversely, following blue light adaptation with orange leads to slow recovery, which is characteristic of orange alone . Recovery from long-wavelength adaptation is slower principally because many rhabdoms seem to delay the onset of regeneration . We suggest that the regeneration system is itself photosensitive, and after orange light adaptation the supply of active chromophore (presumably 11-cis retinal) limits the rate of recovery. Once started, recovery proceeds slowly and continuously, and the total pigment concentration (rhodopsin plus metarhodopsin) in the rhabdomeric membrane remains approximately constant . Within hours after intense adapting exposures, the rhabdoms become altered in appearance, the surfaces become coated with accessory pigment, and the bands of microvilli are less distinct . These changes persist until recovery of rhodopsin proceeds, which suggests that visual pigment regeneration results from addition of newly synthesized rhodopsin associated with membrane turnover.

Section: Rhabdom Morphology and Regenerationsupporting

confidence: 91%

Section: Rhabdom Morphology and Regenerationmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Dark regeneration of rhodopsin in crayfish photoreceptors.

Cronin¹,

Goldsmith²

1984

“…The simplest interpretation of these MSP data is that the visual 314 THE JOURNAL OF GENERAL PHYSIOLOGY " VOLUME 79 " 1982 pigment absorbs maximally at 530 nm , and that the 565nm maximum in the spectral sensitivity function is a result of screening of short wavelengths by the nonmigratory accessory pigments of the eye (Goldsmith, 1978 b) . Studies of a white-eyed mutant of the crayfish Procambarus provide additional support for this interpretation (Kong and Goldsmith, 1977) .…”

Section: Introductionmentioning

confidence: 94%

Photosensitivity spectrum of crayfish rhodopsin measured using fluorescence of metarhodopsin.

Cronin¹,

Goldsmith²

1982

Discrepancies exist among spectral measurements of sensitivity of crayfish photoreceptors, their absorption in situ, and the number and absorption spectra of crayfish photopigments that are extracted by digitonin solutions. We have determined the photosensitivity spectrum of crayfish rhodopsin in isolated rhabdoms using long wavelength fluorescence emission from crayfish metarhodopsin as an intrinsic probe. There is no measurable metarhodopsin in the darkadapted receptor, so changes in the emission level are directly proportional to metarhodopsin concentration. We therefore used changes in metarhodopsin fluorescence to construct relaxation and saturation ("photoequilibrium") spectra, from which the photosensitivity spectrum of crayfish rhodopsin was calculated. This spectrum peaks at -530 nm and closely resembles the previously measured difference spectrum for total bleaches of dark-adapted rhabdoms . Measurements of the kinetics of changes in rhabdom fluorescence and in transmittance at 580 nm were compared with predictions derived from several model systems containing one or two photopigments . The comparison shows that only a single rhodopsin and its metarhodopsin are present in the main rhabdom of crayfish, and that other explanations must be sought for the multiple pigments seen in digitonin solution . The same analysis shows that there is no detectable formation of isorhodopsin in the rhabdom.

“…The rhodopsin of E. superba forms a stable metarhodopsin and is therefore similar to the rhodopsins of several other crustaceans (Goldsmith et al ., 1968 ;Kong and Goldsmith, 1977 ;Wald and Hubbard, 1957) . However, E. superba rhodopsin is unusual in having a spectrum that varies with the pH of the extract.…”

mentioning

confidence: 99%

Euphausiid visual pigments. The rhodopsins of Euphausia superba and Meganyctiphanes norvegica (Crustacea, Euphausiacea).

Denys¹,

Brown²

1982

The rhabdoms of Euphausia superba contain one digitonin-extractable rhodopsin, /Xmax 485 nm . The rhodopsin undergoes unusual pH-dependent spectral changes : above neutrality, the absorbance decreases progressively at 485 nm and rises near 370 nm . This change is reversible and appears to reflect an equilibrium between a protonated and an unprotonated form of the rhodopsin Schiff-base linkage . Near neutral pH and at 10°C, the rhodopsin is partially converted by 420-nm light to a stable 493-nm metarhodopsin . The metarhodopsin is partially photoconverted to rhodopsin by long-wavelength light in the absence of NH20H ; in the presence of NH20H, it is slowly converted to retinal oxime and opsin . The rhodopsin of Meganyctiphanes norvegica measured in fresh rhabdoms by microspectrophotometry has properties very similar to those of the extracted rhodopsin of E. superba. Its Jtn,. . is 488 nm and it is partially photoconverted by short wavelength irradiation to a stable photoconvertible metarhodopsin similar to that of E. superba. In the presence of light and NH20H, the M. ncmegica metarhodopsin is converted to retinal oxime and opsin . Our results indicate that previous determinations of euphausiid rhodopsin absorbance spectra were incorrect because of accessory pigment contamination .