Siderophore-iron uptake in saccharomyces cerevisiae. Identification of ferrichrome and fusarinine transporters.

A family of four putative transporters (Arn1p-4p) in Saccharomyces cerevisiae is expressed under conditions of iron deprivation and is regulated by Aft1p, the major iron-dependent transcription factor in yeast. One of these, Arn3p/Sit1p, facilitates the uptake of ferrioxamine B, a siderophore of the hydroxamate class. Here we report that ARN family members facilitated the uptake of iron from the trihydroxamate siderophores ferrichrome, ferrichrome A, and triacetylfusarinine C. Uptake of siderophore-bound iron was dependent on either the high-affinity ferrous iron transport system or the ARN family of transporters. The specificity of each siderophore for individual transporters was determined. Uptake of ferrichrome and ferrichrome A was facilitated by both Arn1p and Arn3p. Uptake of triacetylfusarinine C was facilitated by Arn2p, although small amounts of uptake also occurred through Arn1p and Arn3p. In contrast to the trihydroxamates, uptake of iron from the dihydroxamate rhodotorulic acid occurred only via the high-affinity ferrous iron system. Epitope-tagged Arn1p was expressed in intracellular vesicles in a pattern that was indistinguishable from that of Arn3p, whereas Ftr1p, a component of the high-affinity ferrous system, was expressed on the plasma membrane. These data indicate that S. cerevisiae maintains two systems of siderophore uptake, only one of which is located on the plasma membrane.

Oximetry of retinal vessels by dual-wavelength imaging: calibration and influence of pigmentation.

A method for noninvasive measurement of Hb O2 saturation (SO2) in retinal blood vessels by digital imaging was developed and tested. Images of vessels were recorded at O2-sensitive and O2-insensitive wavelengths (600 and 569 nm, respectively) by using a modified fundus camera with an image splitter coupled to an 18-bit digital camera. Retinal arterial SO2 was varied experimentally by having subjects breathe mixtures of O2 and N2 while systemic arterial SO2 was monitored with a pulse oximeter. Optical densities (ODs) of vascular segments were determined using a computer algorithm to track the path of reflected light intensity along vessels. During graded hypoxia the OD ratio (ODR = OD600/OD569) bore an inverse linear relationship to systemic SO2. Compensation for the influence of choroidal pigmentation significantly reduced variation in the arterial SO2 measurements among subjects. An O2 sensitivity of 0.00504 +/- 0.00029 (SE) ODR units/%SO2 was determined. Retinal venous SO2 at normoxia was 55 +/- 3.38% (SE). Breathing 100% O2 increased venous SO2 by 19.2 +/- 2.9%. This technique, when combined with blood flow studies in human subjects, will enable the study of retinal O2 utilization under experimental and various disease conditions.

Retinal oxygen consumption during hyperglycemia in patients with diabetes without retinopathy.

OBJECTIVE: This study aimed to determine whether retinal oxygen consumption in patients with diabetes without retinopathy is affected by acute changes in blood glucose. DESIGN: The study design was a nonrandomized, interventional clinical study. PARTICIPANTS: The study consisted of 12 patients with diabetes without ophthalmoscopically visible diabetic retinopathy whose ages were 20 to 59 years (mean, 33.7 years). INTERVENTION: Retinal vessel oximetry was performed on subjects during normoglycemia and during acutely induced hyperglycemia. Hyperglycemia was achieved with the ingestion of an oral glucose load. MAIN OUTCOME MEASURES: Changes in retinal arterial and venous blood oxygen saturation resulting from systemic blood glucose changes were measured. Measurements were made using a noninvasive, two-wavelength digital imaging retinal vessel oximeter. RESULTS: In each subject, the measured retinal venous blood oxygen saturation decreased significantly during hyperglycemia. The amount of decrease in venous oxygen saturation associated with hyperglycemia was positively correlated with the duration of diabetes. The measured retinal arterial oxygen saturation did not change significantly during hyperglycemia. CONCLUSIONS: These results, taken with the observations of numerous other investigators that show increased blood flow during acute hyperglycemia, provide evidence of substantially increased retinal oxygen consumption during hyperglycemia. The results also complement previous observations of the effect of diabetes on retinal autoregulation.

Alterations in viscosity and filterability of whole blood and blood cell subpopulations in diabetic cats.

Capillary closure and venous dilatation occur early in diabetic retinopathy, and altered blood rheology may play a role. For example previous studies have shown leukocytes are less deformable, are more activated, and occlude retinal capillaries more often in diabetic subjects. The purpose of this study was to determine if rheologic changes developed in diabetic cats, a model in which we have documented retinal capillary basement membrane thickening, microaneurysms, and intraretinal hemorrhage characteristics of early diabetic retinopathy. Viscosity of blood, plasma and purified erythrocyte suspensions was measured by rotational viscometry and plasma fibrinogen content was determined by heat precipitation. Filterability of blood and purified erythrocyte, mononuclear leukocyte, and granulocyte suspensions was determined at constant flow, measuring the increase in pressure over 2 min relative to the pressure generated by buffer alone. Viscosity of whole blood and plasma, but not erythrocytes, was significantly elevated (P < 0.005) in the diabetic cats over normals at all shear rates studied (450, 225 and 90 sec-1). Furthermore, fibrinogen levels were significantly elevated in diabetic cats compared to normals (P < 0.004), and were positively correlated with the viscosity of whole blood and plasma. The filterability of mononuclear leukocytes and whole blood in diabetic cats was decreased 56% and 74% when compared to normals, P < 0.0006 and P < 0.025, respectively. In contrast, the filterability of granulocytes and erythrocytes was not significantly different between the two groups. These results suggest that the rheologic alterations in diabetes are numerous, and involve both cellular and plasma protein changes.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple method for practicing unimanual pars plana vitrectomy with the binocular indirect ophthalmoscope.

Bimanual vitrectomy has become the method of choice for performing closed vitrectomy. In certain situations, visualization is improved by using indirect ophthalmoscopy to see the vitrectomy instrument. A simple method using a +20.00-diopter condensing lens is described as a means of practicing the initially difficult unimanual technique, which requires working in an inverted operative field.

A physical analysis of the factors that determine the contour of the iris.

By solving equations that result from the application of basic newtonian physical principles, I developed a model that can predict the profile of the iris by using only the pupil radius, the iris root radius, and the anterior displacement of the pupil from the iris root. The model requires some theoretically and clinically reasonable assumptions regarding the relative importance of forces acting on the iris. Former analyses made false assumptions about contact between the lens and the iris, as well as inappropriate substitution of the physical concept of force for tension. The validity of the new model and its inherent assumptions can now be tested with biometric measurements made in normal eyes and eyes with shallow anterior chambers.

Exudative retinal detachment after photodynamic injury.

Exudative retinal detachments occur in a variety of retinal and choroidal diseases. We created serous retinal detachment in the cat eye by means of photodynamic injury produced by activation of intravascular rose bengal using filtered, focused light (550 nm). Fluorescein angiography later revealed focal retinal and choroidal vascular occlusion surrounded by a larger area of leakage through the pigment epithelium. Serous retinal detachments occurred rapidly, gradually enlarged over the next 3 days, and resolved in all eyes after 14 to 21 days. Histopathologic and ultrastructural features of early lesions included the accumulation of proteinaceous fluid in the subretinal space, pigment epithelial cell damage, and localized occlusion of retinal vessels and the choriocapillaris. Later changes consisted of limited regeneration of the retina and portions of the tapetum. In several respects, these experimental detachments resemble the serous retinal detachments associated with choroidal ischemia in humans, and may serve as a useful model in the study of choroidal microvascular hypoperfusion.

Accuracy of topographic measurements with the Optic Nerve Head Analyzer.

We used a plastic model of the human eye to study the accuracy with which the Optic Nerve Head Analyzer estimates the surface contour and two-dimensional size of the optic nerve head. Computer-generated contour lines were similar to the actual cross-sectional contour of plastic cups as photographed by scanning electron microscopy. The magnification error of computer-measured cup diameters was inversely related to the axial length of the model. The slope of this relationship was reduced with the use of either refraction or axial length as a correction factor for magnification error. Of the two correction factors, the former provided the closest estimation of the known diameters in the phakic model, while the latter performed better in the aphakic model.

Photochemical initiation of thrombosis. Fluorescein angiographic, histologic, and ultrastructural alterations in the choroid, retinal pigment epithelium, and retina.

A new method of producing vascular occlusion, photochemical activation of intravenously injected rose bengal, was used to produce experimental thrombosis of the preretinal and choroidal blood vessels in rabbit eyes. Fluorescein angiography and light and electron microscopy were used to describe the resultant pathologic alterations over time. As early as one hour after treatment, the endothelium of both preretinal and choroidal blood vessels was severely damaged or completely obliterated, and platelet aggregates occluded the vascular lumina. Occlusion of the preretinal and choroidal blood vessels persisted for up to three days; however, endothelial regeneration and reperfusion had occurred in both vascular beds by seven days. In addition, the retinal pigment epithelium and myelin wings suffered ischemic damage. The retinal pigment epithelium began to recover by seven days, but the myelin wings appeared to be irreversibly damaged.

Refractive changes from use of silicone oil in vitreous surgery.

When silicone oil fills the vitreous cavity of the phakic eye or the entire aphakic eye, the refractive correction can be expected to change by 5-9 diopters and sometimes as much as 14 diopters. Aphakic eyes become less hyperopic when filled with silicone oil, whereas phakic eyes become more hyperopic when the vitreous cavity is filled with silicone oil. Previously emmetropic aphakic eyes that are filled with silicone oil have only 4-6 diopters of hyperopia, whereas the same eyes have 10-12 diopters of hyperopia before insertion or after removal of silicone oil. Phakic eyes develop 5-7 diopters of hyperopia when the vitreous cavity is filled with silicone oil, and this puts them in the same range as the silicone oil filled aphakic eyes. High myopia, incomplete silicone oil filling, and several other factors influence the final optical outcome. The vitreoretinal surgeon must anticipate significant changes in refractive error when silicone is introduced into an eye or removed from the eye. Careful retinoscopy and refraction is essential for obtaining optimal vision in these patients.

A new method for vascular occlusion. Photochemical initiation of thrombosis.

A new photochemical method has been used to produce focal thrombosis and occlusion of the blood vessels on the surface of the myelin wings of rabbit retinas. Following intravenous injection of rose bengal, the vessels next to the disc on the nasal wing were exposed to filtered light (550 nm, the absorption maximum of rose bengal) for four minutes. As a control, the vessels on the temporal wing of each rabbit eye were exposed to filtered light for four minutes before the injection of rose bengal. Complete vascular occlusion was produced on the nasal wing in all eyes, with no visible alterations on the temporal wing. Progressive reopening of the arteries on the nasal wing was observed at three days, with reopening of the veins visible by seven days. Reperfusion of capillaries had occurred by 21 days. Light and electron microscopic examination of blood vessels on the nasal wing after light exposure with rose bengal showed disrupted endothelial cells in all exposed blood vessels and platelet aggregates in the arteries and arterioles. No morphologic abnormalities were observed in the temporal wings. This method should be useful in studying the effects of vascular occlusion in the retina and could lead to a new treatment modality for subretinal, iris, or corneal neovascularization.

Epstein-Barr viral antibodies in multifocal choroiditis and panuveitis.

A syndrome of multifocal choroiditis, pigment epithelial disturbance, and inflammatory vitreous cells was found to be associated with Epstein-Barr virus specific antibodies. The ten patients in this series had positive viral capsid antigen IgM or Epstein-Barr early antigen antibody titers. Patients with this syndrome were generally healthy and had no history of a clinical episode of infectious mononucleosis. No patient from the control group with other ocular diseases had positive viral capsid antigen IgM or early antibody titers. All patients in the study group and most of the control patients had viral capsid antigen IgG and Epstein-Barr nuclear antigen antibodies, indicating a previous exposure to the virus as expected in an adult population.

The test light affects quantitation of the afferent pupillary defect.

Nineteen patients with afferent pupillary defects (APDs) from a variety of lesions were examined using a brighter and dimmer test light. A denser neutral density filter was required to balance the afferent defect using the brighter test light in every case. For quantitation of an afferent defect to have meaning, the test light used must be specified. An indirect ophthalmoscope set to 6 V and held 1 foot from the eyes will allow easier detection of subtle relative APDs than it will if set to 3 V.

Computerized scoring and graphing of the Farnsworth-Munsell 100-hue color vision test.

The Farnsworth-Munsell 100-hue test is a sensitive and accurate test of color discrimination. A major disadvantage of the test is the laborious and time-consuming calculation needed to score the results and plot them on a chart for interpretation. We present a computer program, written in Microsoft's BASIC language, that performs the calculation and reports both the individual color cap error scores (from which the graph is plotted) and the total error score. If used with an IBM personal computer (or compatible) capable of graphics, the program plots a graph in a modified polar coordinate format that can be printed on a dot-matrix printer.

Computer-assisted composition and reproduction of ophthalmic documentation.

We use computer software graphics (MacPaint) to create individualized drawings that can be reproduced as high-resolution printouts, kept in disk storage, or transmitted via telephone lines.