Retinitis pigmentosa (RP) is a label for a group of diseases caused by a large number of mutations that result in rod photoreceptor cell death followed by gradual death of cones. The mechanism of cone cell death is uncertain. Rods are a major source of oxygen utilization in the retina and, after rods die, the level of oxygen in the outer retina is increased. In this study, we used the rd1 mouse model of RP to test the hypothesis that cones die from oxidative damage. A mixture of antioxidants was selected to try to maximize protection against oxidative damage achievable by exogenous supplements; ␣-tocopherol (200 mg͞kg), ascorbic acid (250 mg͞kg), Mn(III)tetrakis (4-benzoic acid) porphyrin (10 mg͞kg), and ␣-lipoic acid (100 mg͞kg). Mice were treated with daily injections of the mixture or each component alone between postnatal day (P)18 and P35. Between P18 and P35, there was an increase in two biomarkers of oxidative damage, carbonyl adducts measured by ELISA and immunohistochemical staining for acrolein, in the retinas of rd1 mice. The staining for acrolein in remaining cones at P35 was eliminated in antioxidant-treated rd1 mice, confirming that the treatment markedly reduced oxidative damage in cones; this was accompanied by a 2-fold increase in cone cell density and a 50% increase in medium-wavelength cone opsin mRNA. Antioxidants also caused some preservation of cone function based upon photopic electroretinograms. These data support the hypothesis that gradual cone cell death after rod cell death in RP is due to oxidative damage, and that antioxidant therapy may provide benefit. oxidative damage ͉ photoreceptors ͉ retinal degenerations R etinitis pigmentosa (RP) refers to a group of diseases in which a mutation results in death of rod photoreceptors followed by gradual death of cones. The diseases referred to as RP show a similar phenotype consisting of pigmented spots scattered throughout the retina, narrowed retinal vessels, and retinal sheen suggesting atrophy. At one time, it was felt that inflammation was important in the pathogenesis, and hence the term ''retinitis'' was paired with a descriptor for the most prominent feature of the phenotype, the scattered pigment, resulting in the term retinitis pigmentosa. It is now known that this phenotype results whenever there is widespread rod photoreceptor cell death. Although toxins or infections can occasionally cause widespread rod death, it occurs most commonly when there is a mutation in a gene that is selectively expressed in rods and, either through gain or loss of function, the mutation promotes rod cell death. Mutations in 36 different genes have been found to cause RP, and mutations in many more cause widespread rod cell death in association with syndromes that have extraocular manifestations (www.sph.uth.tmc.edu͞RetNet͞ sum-dis.htm).How does diffuse death of rods throughout the retina result in the distinctive phenotype that ophthalmologists recognize as RP? Rods have an intimate relationship, both structurally and functionally, with retinal pigmen...

Type A y-aminobutyric acid (GABAA) receptors are a family of ligand-gated chloride channels that are the major inhibitory neurotransmitter receptors in the nervous system. Molecular cloning has revealed diversity in the subunits that compose this heterooligomeric receptor, but each previously elucidated subunit displays amino acid similarity in conserved structural elements. We have used these highly conserved regions to identify additional members of this family by using the polymerase chain reaction (PCR). One PCR product was used to isolate a full-length cDNA from a human retina cDNA library. The mature protein predicted from this cDNA sequence is 458 amino acids long and displays between 30 and 38% amino acid similarity to the previously identified GABAA subunits. This gene is expressed primarily in the retina but transcripts are also detected in the brain, lung, and thymus. Injection of Xenopus oocytes with RNA transcribed in vitro produces a GABA-responsive chloride conductance and expression of the cDNA in COS cells yields GABA-displaceable muscimol binding. These features are consistent with our identification of a GABA subunit, GABA Pl, with prominent retinal expression that increases the diversity and tissue specificity of this ligand-gated ion-channel receptor family.

An immortalized cell line was created from a primary culture of bronchial epithelia isolated from a patient with cystic fibrosis. The culture was transformed with a hybrid virus, adeno-12-SV40, which has been used successfully on a number of different human epithelial tissues. The transformed bronchial epithelial cells have the following characteristics. (1) Cyclic adenosine monophosphate (cAMP) is stimulated by beta-adrenergic agonists. (2) Outwardly rectifying Cl- channels are present on the apical cell membrane. These channels can be activated by depolarizing voltages but not by protein kinase A or C. (3) Keratin is present by immunofluorescence, and this is consistent with the epithelial origin of the cells. (4) The SV40 large T antigen is present as demonstrated by immunofluorescence. (5) Multiple karyotype analyses show modal chromosome number to be 80 to 90. There are an average of four chromosome 7 per cell. (6) The phenylalanine508 deletion in the gene coding for the cystic fibrosis transmembrane regulator is present on at least one chromosome. The cells can be grown in multiple passages, contain the abnormal regulation of the secretory Cl- channel, and should be an appropriate substrate for studies of the mutant cystic fibrosis transmembrane regulatory protein and its interaction with the Cl- channel.

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