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S E Ostroy

Publications and source records attributed to S E Ostroy.

At least 19 recordsLinked to original sources
PubMed1998

Altered rhodopsin regeneration in diabetic mice caused by acid conditions within the rod photoreceptors.

PURPOSE: The experiments were designed to provide details on the characteristics of rhodopsin regeneration in the rod photoreceptors of diabetic mice and to evaluate their mechanistic basis. METHODS: A genetically-derived diabetic albino mouse was developed. An excised albino mouse eye preparation was used. The preparation allows for direct measurements of rhodopsin concentration and other spectrally distinct intermediates, and maintains the structural integrity of the compartments involved in rhodopsin regeneration. The experiments were conducted at moderate bleaching levels, averaging 13-14%, with mice that exhibited moderate levels of blood glucose concentration. RESULTS: Rhodopsin regeneration was delayed in both genetically-derived and streptozotocin-injected diabetic mice when compared to non-diabetic mice. During the delay an intermediate of rhodopsin, N-Retinylidene Opsin (NRO440), that precedes the hydrolysis of the bleached chromophore from the opsin and that is associated with acidic conditions was observed. This intermediate was not observed in non-diabetic mice. The delay in rhodopsin regeneration of the diabetic mice was partially eliminated, and the relative concentration of NRO440 was decreased, when the internal pH of the rod photoreceptor was raised by modifying the perfusate composition. CONCLUSIONS: Following a bleach, both genetic and streptozotocin diabetic mice exhibited abnormalities in rhodopsin regeneration. When studied at moderate bleaching levels with animals that were moderately diabetic, both groups of diabetic mice exhibited a delay in the start of the rhodopsin regeneration. The delay appears to be caused by the formation of an acid intermediate of the bleached rhodopsin resulting from acid conditions within the rod photoreceptors.

Acids↗
PubMed1994

Decreased rhodopsin regeneration in diabetic mouse eyes.

PURPOSE: To evaluate the effect of diabetes on rhodopsin regeneration in the excised mouse eye. METHODS: A superfused excised mouse eye preparation that exhibits rhodopsin regeneration after moderate bleaches and that is responsive to the composition of the perfusate was used. Diabetes was induced in albino mice (BALB/c) with the diabetogenic agent streptozotocin. Absorption spectrophotometry of the excised eye was used to monitor rhodopsin concentrations. RESULTS: Significant reductions in rhodopsin regeneration were observed in diabetic mice. Severely diabetic mice exhibited only 64% and 55% regeneration (at perfusate glucose levels of 5.1 mM and 10 mM, respectively), and moderately diabetic mice exhibited 74% and 73% regeneration, compared to the greater than 100% regeneration observed in nondiabetic mice. Glucose perfusate concentration has a major effect on rhodopsin regeneration. Lower concentrations of perfusate glucose (3 mM) reduced the amount of rhodopsin regeneration in both nondiabetic mice and diabetic mice. The diabetic mice seemed to tolerate higher concentrations of perfusate glucose (20 mM) better than the nondiabetic mice. Neither correction for osmolarity nor substitution with a nonglycolytic substrate increased the amount of rhodopsin regeneration in the diabetic mice. CONCLUSIONS: Diabetes reduced the amount of rhodopsin regeneration that followed moderate bleaches in excised mouse eyes. The data suggest that some process or processes associated with rhodopsin regeneration have been affected in the diabetic.

Animals↗
PubMed1993

Hypoxia inhibits rhodopsin regeneration in the excised mouse eye.

PURPOSE: The goal of this study was to evaluate the effect of oxygen deprivation on rhodopsin regeneration in the excised mouse eye. METHODS: A new preparation for studying rhodopsin regeneration with a superfused excised albino mouse eye was developed. The preparation exhibits multiple regenerations after moderate bleaches (15%-20%) and is sensitive to the composition of the perfusate, allowing reversible testing of conditions. A variety of protocols were used to evaluate the effect of hypoxia. The major experiments varied the timing of the decreased oxygen relative to the illumination: Decreasing the oxygen (1) before the illumination, (2) immediately after the illumination, or (3) some time after the illumination, after half of the rhodopsin had regenerated. Elevated concentrations of extracellular glucose also were used for certain experiments. RESULTS: Regardless of protocol, at low levels of oxygen no rhodopsin regeneration was observed. The effects were reversible, however, and decreased oxygen for up to 3 hr did not diminish the ability of the eye to regenerate rhodopsin after restoration of the oxygen and a subsequent bleach. CONCLUSIONS: Low levels of oxygen eliminated rhodopsin regeneration in the excised eye. The effect could not be offset by high levels of glucose, illumination, or other conditions known to reduce the dependence of photoreceptors on aerobic respiration.

Animals↗
PubMed1992

Extracellular glucose dependence of rhodopsin regeneration in the excised mouse eye.

To study the process of rhodopsin regeneration a superfused excised whole eye preparation of the albino mouse was developed. With this preparation, complete regeneration could be observed after each of the first two illuminations (bleaching 15-20%), and incomplete regeneration after a third illumination. Regeneration was minimal at extracellular glucose concentrations of 0 or 1 mM with improved regenerations at higher concentrations. Maximum regenerations were observed at glucose concentrations of 4-10 mM. First-bleach regenerations were as follows: 0 mM glucose, 20%; 1 mM, 8%; 2 mM, 45%; 3 mM, 82%; 4 mM, 115%; 5.1 mM, 121%; 7 mM, 120%; and 10 mM, 126%. The effects of reduced glucose were reversible. After an initial bleach with 0 or 1 mM extracellular glucose that exhibited minimal regeneration, the re-addition of glucose (5.1 mM) restored the ability of the eye to regenerate rhodopsin following a second bleach, but only to the level prior to that bleach. Mitochondrial substrates fumarate (10 mM) or pyruvate (10 mM) partly substituted for glucose, exhibiting first-bleach regenerations of 56 and 85%, respectively.

Animals↗
PubMed1990

A stage in glycolysis controls the metabolic adjustments of vertebrate rod photoreceptors upon illumination.

The factors affecting the metabolic adjustments of toad rod photoreceptors were studied by monitoring the oxygen utilization of excised retinas and by measuring rod outer segment ATP and GTP concentrations. Respiratory adjustments upon illumination were observed when glucose or fructose was provided in the perfusate, but not when a glycolytic inhibitor was added to the perfusate containing glucose and pyruvate, or when a substrate beyond glycolysis or from a later stage of glycolysis was substituted for glucose. The amplitudes of the respiratory adjustments to illumination were dependent on the concentration of glucose in the perfusate. The ATP and GTP concentration changes were dependent on respiratory adjustments, including glycolytic effects, and on the levels of illumination. The data suggest a control point within glycolysis for light-induced adjustments of respiration, possibly at phosphofructokinase.

Adenosine Triphosphate↗
PubMed1987

Studies of the Drosophila norpA phototransduction mutant. I. Electrophysiological changes and the offsetting effect of light.

The electrophysiological characteristics of norpAH52, a temperature sensitive phototransduction mutant of Drosophila melanogaster, were studied in vivo. Upon raising the environmental temperature to 33-37 degrees C, mutant flies exhibited time-dependent changes in photoresponses. Initial observations were losses in responsiveness at low light intensities and prolonged receptor potential waveforms. Next, reductions in response amplitudes at higher light intensities occurred, until no responses were obtained. On return to lower temperature the electrophysiological properties recovered in reverse order. Based on these observations we conclude that the primary defect of norpA affects the efficiency of the phototransduction process. Enhanced light exposure could offset the receptor potential changes in norpA. With the temperature sensitive mutant: (1) additional light exposure prolonged the time that responses could be observed at the higher temperature, (2) when 1-s illuminations no longer elicited responses at the higher temperature, 1-min illuminations at the same intensity temporarily restored the ability to obtain 1-s-responses, and (3) light accelerated the restoration of responses on return to lower temperature. Illumination also had an effect on non-temperature sensitive norpA mutants, enabling the production of small photoresponses in norpAH44, a mutant that normally does not exhibit any responses, and improving the low-light-intensity responses of norpAP16. Our study indicates that the PI cycle, which is inhibited in norpA mutants (Yoshioka et al. 1985), is an important light-sensitive positive step or effector in the production of receptor potential responses.

Animals↗
PubMed1987

Studies of the Drosophila norpA phototransduction mutant. II. Photoreceptor degeneration and rhodopsin maintenance.

The norpAH44 phototransduction mutant of Drosophila melanogaster, an allele that, on eclosion, does not exhibit a receptor potential was found, at later ages, to undergo light and temperature dependent degeneration of its photoreceptors as well as decreases in rhodopsin concentration. Pseudopupil measurements and light and electron microscopy were used to monitor the structure of the photoreceptors. When norpAH44 flies were maintained exclusively in the dark, no changes in structure or rhodopsin concentration were observed. When maintained on a 12 h light-12 h dark cycle, structural changes were first observed at 6 days of age for flies maintained at 24 degrees C or at 12 days of age for flies maintained at 19 degrees C. When the light-dark cycle was initiated after 10 days in the dark there was a more rapid loss of rhodopsin concentration and pseudopupil. The data suggest that even in the dark, although no obvious changes in structure or rhodopsin concentration were observed, certain processes that support these components had been affected. NorpAP12, an allele that exhibits small receptor potential amplitudes, also displayed age- and light-dependent photoreceptor degeneration and decreases in rhodopsin concentration, whereas no degeneration or decreases in rhodopsin were observed in norpAP16, an allele that exhibits receptor potential amplitudes similar to those of wild-type. The data suggest that the processes that affect phototransduction, such as the phosphatidylinositol cycle, have a long-term role in the maintenance of rhodopsin concentration and photoreceptor integrity.

Alleles↗
PubMed1987

Factors affecting the regeneration of rhodopsin in the isolated amphibian retina.

The capacity of isolated perfused frog and toad retinas to regenerate rhodopsin after a series of low level bleaches was investigated. For bleaches of less than 2% complete regeneration was observed after the first bleach with less or no regeneration after subsequent bleaches. Total regeneration from all bleaches was approximately 3%, an amount consistent with stores of 11-cis retinol in amphibian rod outer segments. Total regeneration was increased by incubation with membrane impermeable reagents that oxidize retinol to retinal and was reduced by higher levels of bleaching or added cGMP. It was eliminated by the substitution of 2-deoxy-D-glucose and pyruvate for glucose.

Animals↗
PubMed1986

The effects of hepes, bicarbonate and calcium on the cGMP content of vertebrate rod photoreceptors and the isolated electrophysiological effects of cGMP and calcium.

To evaluate the role of cGMP in vertebrate rod photoreceptors, two extracellular effectors of cGMP were used (calcium and buffer), and both cGMP content and electrophysiological responses were measured. In the dark when the cGMP content was reduced by 80%, electrophysiological effects mimicking a weak background light were observed. Continuous illumination, sufficient to suppress all electrophysiological responses, had only minor effects on cGMP. The data seem inconsistent with suggestions that steady-state levels of cGMP alone control the light responses of rod photoreceptors. The electrophysiological effects of extracellular calcium (under conditions of unaltered cGMP) were distinguishable from those of cGMP.

Action Potentials↗
PubMed1984

Pathways in the hydrolysis of vertebrate rhodopsin.

A direct method for measuring the amount of retinal 387 was used along with spectral techniques to measure each of the intermediates in the photolysis of rhodopsin and to unequivocally determine the pathways in solution extracts of bovine rhodopsin and excised toad and skate retinas. Metarhodopsin II 380 was the earliest intermediate which hydrolyzed to retinal 387 plus opsin. In excised toad retinas three approaches were used to show that Meta III 465 decayed directly to retinal 387 plus opsin. The only pathway consistent with the data was: (Formula: See text). In solution extracts the formation and hydrolysis of N-Retinylidene-Opsin was also observed.

Animals↗
PubMed1979

Renewal of opsin in the photoreceptor cells of the mosquito.

Mosquito rhodopsin is a digitonin-soluble membrane protein of molecular weight 39,000 daltons, as determined by sodium dodecyl sulfate gel electrophoresis. The rhodopsin undergoes a spectral transition from R515-520 to M480 after orange illumination. The visual pigment apoprotein, opsin, is the major membrane protein in the eye. Protein synthesis in the photoreceptor cells occurs in the perinuclear cytoplasm and the newly made protein is transported to the rhabdom. Light adaptation increases the rate of turnover of this rhabdomal protein. The turnover of electrophoretically isolated opsin is also stimulated by light adaptation. The changes observed in protein metabolism biochemically, are consistent with previous morphological observations of photoreceptor membrane turnover. The results agree with the hypothesis that the newly synthesized rhabdomal protein is opsin.

Adaptation, Physiological↗