L-DOPA produced nitric oxide in the vitreous and caused greater vasodilation in the choroid and the ciliary body of melanotic rats than in those of amelanotic rats.

The nitrogen cycle initiates direct reduction of N2 to NH3 by enzymatic reactions. We hypothesize that L-dihydroxyphenylalanine (L-DOPA), a catecholamine, could be a source of nitric oxide (NO). In order to determine whether L-DOPA generates NO and induces any biological change in the eye, we measured the generation of NO in vitro and in vivo, and investigated the histopathological changes caused by injection of L-DOPA into the vitreous of rats. We also hypothesized that melanin granules may affect the generation of NO during the metabolism of L-DOPA, since L-DOPA is a precursor of melanin in the brain and the eye. Therefore, we compared the effects of L-DOPA on the generation of NO between amelanotic and melanotic rats. NO was measured as diffusion currents by NO electrodes. In vitro, various concentrations of L-DOPA (5, 29.9, 79.4, 152.7, and 249 microM) were added to the medium. The inhibition of NO generation by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO) was tested. In vivo, NO generation in the vitreous of rats was measured and the eyes were enucleated under anesthesia after L-DOPA injection. The ocular tissues were subjected to histological examination. NO was produced from L-DOPA in a dose-dependent manner and was scavenged by carboxy-PTIO in vitro. NO in the vitreous of melanotic rats was generated from L-DOPA. Histological examination with hematoxylin-eosin staining revealed vasodilation in the ciliary vessels and the choroid after L-DOPA injection. Both effects were greater in melanotic rats than in amelanotic rats. The vasodilation may be attributable to NO as well as to superoxides, which can be regulated by the existence of melanin.

Phenotype associated with an R120X nonsense mutation in the RP2 gene in a Japanese family with X-linked retinitis pigmentosa.

We examined a Japanese family with X-linked retinitis pigmentosa (RP) associated with a nonsense mutation, R120X, in the RP2 gene. The 26-year-old proband presented at the age of seven years with a two-year history of night blindness. Visual disability worsened with increasing age. At age 24, visual acuity was 0.08 in both eyes. Testing for refractive error indicated mild myopia. Visual fields showed bilateral-constriction to 10 degrees. He had central macular areolar sclerosis in both eyes. Two maternal uncles had vision of light perception to hand movement in their early forties together with dense bilateral cataracts. The ocular phenotype of this family with R120X was considered severe; reported phenotypes associated with this mutation have not been uniform.

Melanin granules prevent the cytotoxic effects of L-DOPA on retinal pigment epithelial cells in vitro by regulation of NO and superoxide radicals.

Inasmuch as the nitrogen cycle elicits the direct reduction of N2 to NH3 through enzymatic reactions, and inasmuch as L-DOPA (L-dihydroxyphentlalamine), a catecholamine, can be a source of nitric oxide (NO), it is possible that melanin granules in the eye affect the generation of NO, which causes damage to the retinal pigment epithelial (RPE) cells during the oxidation of L-DOPA. In order to confirm this possibility, we analyzed the correlations of NO generation, cell growth, and superoxide dismutase (SOD) activities in two types (melanotic and amelanotic) of bovine RPE cells following exposure to L-DOPA. NO generation from L-DOPA was determined using an NO detector that is reliant on redox currents. The concentration of NO was measured in terms of diffusion currents run between a working electrode and a counter electrode, both being set in culture medium placed in a Petri dish. For the assays, L-DOPA was added to the medium at various concentrations (5, 29.9, 79.4, 152.7 or 249 microM), and 6 min after addition, an NO-trapping agent 2,4-carboxyphenyl-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO) was also added. The melanotic and amelanotic types of RPE cells were cultured separately in medium with L-DOPA under an atmosphere containing 20, 10 or 5% oxygen. Cell numbers were counted using a Coulter counter, and SOD activities were determined following incubation for 24, 48 or 72 hr using a modification of the luminol assay. The results obtained indicated that: (a) NO was produced from L-DOPA in a concentration-dependent manner and was trapped quantitatively by carboxy-PTIO; (b) the generation of NO was inhibited more markedly in the melanotic cell line than in the amelanotic one, suggesting an increased tolerance to L-DOPA-derived cytotoxicity in the former; and (c) the SOD activities were more affected by oxygen concentration in the melanotic cells than in the amelanotic ones. From these results, it is concluded that melanin granules in RPE cells have a role in preventing the cytotoxicity derived from L-DOPA and in regulating the generation of NO and superoxide radicals.

Effects of fluorescent light on growth of bovine retinal pigment epithelial cells in vitro incubated with linoleic acid or linoleic acid hydroperoxide.

Light-induced peroxidation of polyunsaturated fatty acids (PUFA) may generate lipid hydroperoxides, which may have toxic effects on retinal pigment epithelial (RPE) cells in vitro. We investigated the effects of cool-white fluorescent light on the RPE cells incubated with linoleic acids (LA) or linoleic acid hydroperoxides (LHP) and the influence of antioxidative enzymes. We measured the bovine RPE cell number after exposure to fluorescent light (610 and 1,200 lux) in the presence of LA or LHP. Furthermore, the effects of superoxide dismutase (SOD) and catalase on LA- or LHP-treated RPE cells were also examined. Both LA and LHP treatment increased RPE cell number under weak illumination (610 lux), but dose-dependently decreased the number of cells exposed to strong illumination (1,200 lux). With exposure to strong illumination, LA caused a greater reduction in RPE cell number than LHP. Multiple linear regression analysis showed that the number of RPE cells was significantly decreased in a manner dependent on the interactions of the illuminance of light and the concentrations of LA or LHP. The antioxidative enzymes significantly ameliorated the damage to RPE cells from LA or LHP and exposure to light. Therefore, the exposure to fluorescent light augmented the cytotoxic effects of LA and LHP on RPE cells, and this effect is likely to be mediated by reactive oxygen species.

The localization of glutathione peroxidase in the photoreceptor cells and the retinal pigment epithelial cells of Wistar and Royal College of Surgeons dystrophic rats.

INTRODUCTION: If degenerating photoreceptor outer segments not phagocytized by RPE cells in the retina of Royal College Surgeons (RCS) rats were to undergo peroxidation, the distribution of glutathione peroxidase (GSH-PO) in the mitochondria or cytoplasm of the retina might be altered. We evaluated the immunocytochemical localization of GSH-PO to identify subcellular organelles in sections of the retinas of RCS rats. METHODS: Immunoblot analysis confirmed the presence of GSH-PO molecules in the retinas of RCS and Wistar rats aged 3 weeks. Sections were reacted with the F(ab) fragment of anti-rat alphaGSH-PO and then examined by laser scanning microscopy (LSM) and transmission electron microscopy (TEM). RESULTS: The size of the GSH-PO molecule in the retina was about 21 KD in the mitochondria and 23 KD in the cytosol in both strains of rats. LSM revealed fluorescent granules in the photoreceptor inner segments of the Wistar rats, and immunohistochemical TEM revealed GSH-PO in the mitochondria of their photoreceptor inner segments and retinal pigment epithelial (RPE) cells. In the RCS rats, the degenerating photoreceptor outer segments were clearly seen to be positive for anti-GSH-PO by conventional light microscopy (CLM). However, the photoreceptor inner segments of the RCS rats were negative for staining with anti-GSH-PO by LSM, and no GSH-PO could be detected in the mitochondria of the photoreceptor inner segments or RPE cells by immuno-TEM. CONCLUSION: Degeneration of the photoreceptor outer segments induced mitochondrial damage in the photoreceptor inner segments, and as a result GSH-PO shifted from the photoreceptor inner segments to the degenerating outer segments.

Visual function and gene analysis in a family with Oguchi's disease.

A family with 1 case of retinitis pigmentosa (III-1) and 2 cases of Oguchi's disease (III-2, 3) was examined in terms of electrophysiology as well as molecular biology. The proband (III-3), a 42-year-old female, and 2 older brothers (III-1, 2, aged 52 and 45 years) and 2 unaffected members in the same family participated in this study. Corrected visual acuities of the individuals with Oguchi's disease (III-2, 3) were 1.2. On funduscopy, blood vessels stood out in relief against a metallic-appearing background and a Mizuo-Nakamura phenomenon was evident. Full-field electroretinograms (ERGs) recorded from the proband were indicative of rod dystrophy, but results of other electrophysiological examinations (multifocal ERG, pattern ERG and visual-evoked cortical potential recordings) were within normal limits. Patient III-1 had corrected visual acuities of RE 20 cm/m.m. and LE 30 cm/n.d., severe chorioretinal atrophy in both fundi, and full-field ERG revealed rod-cone dystrophy. Mutation of the arrestin gene (1147de1A) was detected in all 3 patients. Visual function in each patient coincides with that of retinitis pigmentosa or Oguchi's disease, respectively.

A novel homozygous Ile535Asn mutation in the rod cGMP phosphodiesterase beta-subunit gene in two brothers of a Japanese family with autosomal recessive retinitis pigmentosa.

PURPOSE: Recently, mutations in several genes have been identified as being responsible for the pathogenesis of autosomal recessive retinitis pigmentosa (arRP). These genes include rhodopsin, beta-subunit of rod cGMP phosphodiesterase (PDEB), alpha-subunit of rod cGMP phosphodiesterase (PDEA), and alpha-subunit of rod cGMP-gated channel. We here attempted to identify a novel mutation in the PDEB gene in Japanese arRP patients. METHODS: Using the PCR-SSCP method, sequencing analysis, and restriction endonuclease digestion assay, we analyzed the PDEB gene in 17 Japanese families with non-dominant retinitis pigmentosa. RESULTS: A novel Ile535Asn mutation was identified in two patients in a single family and the mutation cosegregated with RP in this family. Among 90 unrelated healthy individuals, no one was identified as homozygous for this mutation, except for one individual who was found to be heterozygous. CONCLUSIONS: Isoleucine at codon 535 in the PDEB gene is conserved among various mammals. Missense mutations of the PDEB gene causing arRP have been reported in a limited region (codon 527-codon 699) in which codon 535 is located. Thus, the Ile535Asn mutation is an additional missense mutation which is responsible for the pathogenesis of arRP.

Visual function in retinitis pigmentosa related to a codon 15 rhodopsin gene mutation.

To determine the phenotype of a Japanese family in which retinitis pigmentosa cosegregates with a rhodopsin gene mutation, i.e. an asparagine-to-serine change at codon 15 (Asn-15-Ser), 5 affected and 5 unaffected members of one pedigree underwent several ophthalmic examinations as well as Ganzfeld electroretinography (ERG) and multifocal ERG. Genomic DNA samples were analyzed by PCR amplification, sequencing and restriction enzyme digestion. A codon 15 rhodopsin gene mutation (Asn-15-Ser) was found in all affected members. The region of pigmentary degeneration was localized in the lower hemiretina, and visual field defects corresponded to the retinal pigmentary changes. Scotopic ERG amplitudes, rather than photopic ERG amplitudes, were reduced. Multifocal ERG revealed a low magnitude of response density, even for the upper hemiretina, which showed no bony corpuscle pigmentation. Visual function in sectorial retinitis pigmentosa associated with rhodopsin gene codon 15 mutation is on the basis of the rod-cone dystrophy, regardless of differences in phenotypic expression.

Progression of visual field loss in patients with retinitis pigmentosa of sporadic and autosomal recessive types.

PURPOSE: We examined the natural course of patients with retinitis pigmentosa of the eight sporadic and five autosomal recessive forms over 5 years. METHODS: We measured the areas of the visual fields by Goldmann perimetry using a digitizer and a computer software. RESULTS: The visual field of V-4 isopters in 4 sporadic cases was approximately 200 cm2 during 30 years after the initial examination, but decreased down to 40 cm2 in the next 10 years. The visual field was reduced to half the normal field in 3 autosomal recessive cases early below the age of 25 years. In 4 sporadic and 2 autosomal recessive cases, the inferior temporal visual field was the widest at the onset of the disease, but exhibited the most severe loss. The superior nasal area was the narrowest initially, and showed the mildest progression. CONCLUSIONS: The visual field in retinitis pigmentosa is constricted age-dependently with severe loss of the inferior temporal visual area and mild damage to the superior nasal area.

Changes in lipid peroxide level in retinal pigment epithelial cells in vitro upon addition of linoleic acids or linoleic acid hydroperoxides under varying concentrations of oxygen.

We previously observed the presence of autofluorescent lipofuscin or its like in retinal pigment epithelial (RPE) cells, which were incubated with linoleic acid hydroperoxides (LHP). We studied the effect of oxygen on the level of lipid peroxides in RPE cells in the presence of linoleic acids (LA) or LHP. The level of lipid peroxides in these cells was determined by use of the thiobarbituric acid-reactive substance (TBARS), which responded to oxygen concentrations qualitatively, and a linear regression analysis. Multiple linear regression analysis disclosed that treatment with LA for 24 hr resulted in detectable increase in the level of TBARS in the cells, whereas treatment with LA or LHP for 48 hr caused detectable decrease. Stepwise linear regression analysis showed that the level of TBARS decreased in an oxygen-tension dependent manner in the cells incubated with LA for 48 hr. Thus, it was shown that short-term incubation with LA increased the level of TBARS in the cells and that LA decreased its level in an oxygen-tension dependent manner. For these results, the postulation was made that the prolonged auto-oxidation of LA caused production of lipofuscin-like materials, a complex of lipid peroxides and proteins that were insoluble in SDS and acetic acid solution.

X-ray microanalysis and phagocytotic activity of cultured retinal pigment epithelial cells in hypoxia.

PURPOSE: To investigate the influence of the functional and morphological changes induced in retinal pigment epithelial (RPE) cells by retinal ischemia, we evaluated the phagocytotic activity, the concentration of various elements, and ultrastructure in cultured RPE cells in hypoxia. METHODS: The concentrations of oxygen in incubators were adjusted to 20, 10, and 1% by the addition of nitrogen for 72 hr. To observe phagocytotic activity and its relationship to actin filaments, the filaments of RPE cells incubated with fluoresbrite carboxylate YG microspheres were stained with rhodamine phalloidin. Some of the specimens were subjected to X-ray microanalysis by scanning electron microscope after being fixed, freeze-dried, and coated with carbon to investigate the cytoplasmic concentration of elements. A part of the latter specimens was also observed by transmission electron microscope after being embedded in epon and cut into ultrathin sections to see the ultrastructural changes inside cell. RESULTS: Lowering oxygen concentrations from 20% to 1% swelled RPE cells and decreased the number of fluoresbrite carboxylate YG microspheres phagocytized by RPE cells. Phagocytosis of a large amount of latex beads (30 microl) for 24 hr in 1% oxygen caused a disruption of RPE cells. Na, S, and P were detected in RPE cells cultured in 20% oxygen. Reducing the oxygen concentration from 20 to 10 or 1% significantly decreased Na and increased S. Mitochondria were observed in RPE cells in 20 and 10% oxygen, but many vacuoles were observed in the cytoplasm in 1% oxygen. CONCLUSION: Hypoxia as low as 1% oxygen induced malfunction of phagocytosis and the fragility of RPE cells. We could speculate the imbalance of the electrolytes such as Na or a decrease of antioxidants such as glutathione containing S as a reason of disturbance of cell viability.

Multicenter genetic study of retinitis pigmentosa in Japan: I. Genetic heterogeneity in typical retinitis pigmentosa.

A nationwide, multicenter study of typical retinitis pigmentosa (RP) was carried out in collaboration with 18 hospitals throughout Japan to obtain current information for genetic counseling. We analyzed the genetic heterogeneity of RP based on the parental consanguinity of 434 probands registered during a 6-month period in 1990. A gradual decline in the frequency of consanguineous marriage was recognized among the normal parents of RP patients. The relative frequencies of inheritance patterns were estimated as: autosomal recessive, 25.2%; autosomal dominant, 16.9%; X-linked, 1.6%; and simplex, 56.3%. A comparison of these results with previous reports in Japan revealed a decline in the relative frequency of autosomal recessive cases and an increase in simplex cases. This suggests a decrease in the incidence of autosomal recessive retinitis pigmentosa in Japan, as well as the necessity for exhaustive investigations aimed at identifying inheritance patterns for RP patients seeking genetic counseling.

Multicenter genetic study of retinitis pigmentosa in Japan: II. Prevalence of autosomal recessive retinitis pigmentosa.

Retinitis pigmentosa (RP) is a group of genetically heterogeneous diseases with autosomal recessive (AR), autosomal dominant, and X-linked modes of inheritance. Autosomal recessive retinitis pigmentosa (ARRP) is the most common form in Japan. A genetic analysis was done to determine the prevalence of ARRP indirectly, to provide an estimation of changing trends in the overall prevalence of RP. Data on the frequency of consanguinity and marriage year of normal parents of 59 ARRP patients were obtained from a nationwide multicenter survey of typical retinitis pigmentosa conducted in 1990. The gene frequency of ARRP was 0.01145 (Dahlberg's formula). In 1990, the number of young symptomatic ARRP patients decreased, while the number of patients aged 40 years and older increased. The total number of symptomatic ARRP patients in 1990 was nearly 21% higher than in 1970. Despite a dramatic decline in consanguinity in recent decades in Japan, the number of ARRP patients has increased. This increase is attributed to greater longevity and overall population growth. Our results suggest that the total number of RP patients has not decreased, and may even have increased.

Histology of fetal eyes with oculocutaneous albinism.

The diagnosis of tyrosinase-negative oculocutaneous albinism (OCA) was made in a 19-week-old fetus by skin biopsy. Because the parents had an 11-year-old son with tyrosinase-negative OCA, they requested that the fetus be aborted at the 20th week of gestation. A histological analysis of the eyes was performed. Throughout the retina, the ganglion cell layer was separated from the inner neuroblastic layer by the inner plexiform layer. However, the number of ganglion cells was decreased and the nerve fiber layer was immature. Bipolar and horizontal cells had begun to segregate into the inner nuclear layer. Rods and cones were identifiable in the posterior, but not peripheral, retina. Cones were more numerous in the center of the retina, and no rod-free area was identifiable. In addition, the ciliary body (epithelial folds, blood vessels in the mesodermal connective tissue core, and ciliary muscle) was less developed than in a normal fetus. Melanosomes in the retinal pigment epithelium only contained filaments without melanization and were therefore classified as stage I or II melanosomes. However, the ciliary epithelium also contained some stage III melanosomes with melanin adherent to the filaments.

Comparative effects of linoleic acid and linoleic acid hydroperoxide on growth and morphology of bovine retinal pigment epithelial cells in vitro.

PURPOSE: Outer segments of the photoreceptor rods that are phagocytized by the retinal pigment epithelial (RPE) cells contain a high proportion of polyunsaturated fatty acids (PUFA). PUFA are susceptible to lipid peroxidation. We hypothesized that the resulting peroxides could injure RPE cells leading to retinal degeneration. Accordingly, we compared the effects of linoleic acid (LA) and its hydroperoxide (LHP) on the growth and morphology of RPE cells using laser scanning microscopy and transmission microscopy. METHODS: We counted the number of RPE cells after incubation for 24 and 48 hrs with concentrations of LA or LHP of 0.035, 0.175, and 0.35 mM. To observe the actin filaments, cultured RPE cells were stained with rhodamine phalloidin. The cells were prefixed with 2% glutaraldehyde and postfixed in 1% osmium tetroxide. Specimens were embedded in Epon 812 after dehydration, and the ultrathin sections were doubly stained with 2% uranyl acetate and 2% lead acetate for examination by transmission electron microscopy. RESULTS: Exposure to LA or LHP produced dose-dependent damage to RPE cells with a significantly greater effects of LHP than LA. After incubation for 24 hrs with 0.35 mM LA, the number of vacuoles in RPE cells exceeded that observed in control RPE cells by 365 nm laser microscopy. Exposure to 0.35 mM LHP for 24 hrs produced a pycnotic nucleus, with diffuse and granular autofluorescences observed in and around it. Exposure of RPE cells to 0.35 mM LA for 24 hrs showed that the LA incorporated into the lysosomes was digested and released extracellularly from lysosomes via exocytotic vesicles. However, such exposure to LHP damaged the RPE cells, including the membranes in the pinocytotic vesicles. The packed membranes resembled myelin. CONCLUSIONS: While the LA incorporated into the lysosomes was released extracellularly, LHP persisted in the RPE cells, being observed as autofluorescent lipofuscin-like materials. LHP was cytotoxic, and caused damage to the membranes of pinocytotic vesicles and lysosomes.

[Aging changes in conjunctiva visualized by fluorescein angiography and histopathology].

In order to investigate the aging changes of the conjunctiva, we examined fluorescein-positive areas by fluorescein angiography. The deposition of melanin in basal cells, the degranulation of mast cells, and the lumens of capillaries were examined by light microscopy in 35 cataractous eyes without diabetes or hypertension. The fluorescein leakage increased with aging. The number of basal cells with deposition of melanin granules and mast cells with degranulation correlated significantly with aging. On the other hand, the narrowing of capillary lumens in conjunctival stroma was not observed with aging. Based on the above results, we conclude that the weakness of the conjunctival vessels without the narrowing of capillary lumens might be caused by functional disorder of the endothelium and pericytes. The increase of deposition of melanin granules in basal cells may be caused by the breakdown of the metabolic pathway of melanin. Long-time mechanical stimuli and metabolic disorders of active substances may increase the degranulation of mast cells.

Effects of superoxide dismutase and catalase on growth of retinal pigment epithelial cells in vitro following addition of linoleic acid or linoleic acid hydroperoxide.

The rod outer segments of the retina that are phagocytized by retinal pigment epithelial (RPE) cells are susceptible to lipid peroxidation because of their high content of polyunsaturated fatty acids. Linoleic hydroperoxides (LHP), synthesized by peroxidation of linoleic acids (LA), produce greater damage to retinal function than does LA. We compared the effects of LHP and LA on the growth of cultured chick embryonic RPE cells and analyzed a model of data sets using multiple linear regression for the number of cells as a function of time. The spectrum of LA had a sharp peak at 205 nm and a broad spectrum at 235 nm, while LHP had only a broad spectrum at 235 nm. Exposure to LA and LHP caused dose-dependent damage of chick embryonic RPE cells: they were significantly more affected by the addition of LHP than LA. The antioxidative enzymes catalase and superoxide dismutase minimized damage to the RPE cells caused by LHP in proportion to the enzyme concentration. However, RPE cells incubated with LA were more affected by the enzymes than when no enzymes were added.

[Electron microscopic studies of retinal pigment epithelial cells incubated with L-dopa in 10% and 20% oxygen].

In order to make clear how the ultrastructure of the bovine second-passage retinal pigment epithelium (RPE) was affected by exposure to L-dopa and oxygen, we compared the toxic effects of melanotic and amelanotic RPE. The oxygen levels in the incubators and the L-dopa concentrations in the media were adjusted to 10% or 20% oxygen by adding nitrogen gas and 100 microM or 250 microM L-dopa, respectively. After 24 hours, melanotic and amelanotic RPE were fixed and embedded in epon. Ultrathin sections were examined by transmission electron microscopy. Rough endoplasmic reticula were found to be dilated and ribosomes were extinguished in both melanotic and amelanotic RPE. The damage by L-dopa in melanotic RPE was less than that in amelanotic RPE and less in 10% oxygen than in 20% oxygen.

Nucleotide sequence and regulation of a new putative cell wall hydrolase gene, cwlD, which affects germination in Bacillus subtilis. .

DNA sequencing of a region upstream of the mms223 gene of Bacillus subtilis showed the presence of two open reading frames, orf1 and orf2, which may encode 18- and 27-kDa polypeptides, respectively. The predicted amino acid sequence of the latter shows high similarity to a major autolysin of B. subtilis, CwlB, with 35% identity over 191 residues, as well as to other autolysins (CwlC, CwlM, and AmiB). The gene was tentatively named cwlD. Bright spores produced by a B. subtilis mutant with an insertionally inactivated cwlD gene were committed to germination by the addition of L-alanine, and spore darkening, a slow and partial decrease in A580, and 72% dipicolinic acid release compared with that of the wild-type strain were observed. However, degradation of the cortex was completely blocked. Spore germination of the cwlD mutant measured by colony formation after heat treatment was less than 3.7 x 10(-8). The germination deficiency of the cwlD mutant was only partially removed when the spores were treated with lysozyme. Analysis of the chromosomal transcription of cwlD demonstrated that a transcript (RNA2) appearing 3 h after initiation of sporulation may have originated from an internal sigma E-dependent promoter of the cwlD operon, and a longer transcript (RNA1) appearing 4.5 h after sporulation may have originated from a sigma G-dependent promoter upstream of the orf1 gene. The cwlD mutant harboring a B. subtilis vector plasmid containing the intact cwlD gene recovered germination at a frequency 26% of the wild-type level.

[The effects of dopa and oxygen on RNA concentrations in cultured chick embryonal retinal pigment epithelial cells].

We measured RNA and DNA concentrations in cultured chick embryonal retinal pigment epithelial cells to investigate the effects of dopa and oxygen on DNA and RNA synthesis. RNA/DNA ratios were decreased by addition of 250 microM dopa. Decrease of RNA/DNA ratios was suppressed when the oxygen concentrations were reduced from 20% to 10%. Incubation with medium containing 100 microM dopa increased RNA/DNA ratios in 10% oxygen. Exposure of retinal pigment epithelial cells to 250 microM dopa caused the decrease of RNA concentrations in the retinal pigment epithelial cells, which was ameliorated by lowering oxygen concentrations. However, the addition of 100 microM dopa in 10% oxygen stimulated retinal pigment epithelial cells and seemed to increase RNA concentrations.