Sided effects of bicarbonate on rabbit corneal endothelium in vitro

Effect of bicarbonate-free balanced salt solutions on fluid pump and endothelial morphology of rabbit corneas in-vitro

Corneas from young adult albino rabbits were exposed, in-vitro, to various bicarbonate-free balanced salt solutions under an applied hydrostatic pressure of 20 cmH2O at 35 degrees C for up to 4.5 h. The solutions were buffered with a HEPES-MOPS mixture, phosphate salts or acetate-citrate salts (pH 7.1-7.4). All of these solutions support a net fluid pump activity attributed to the corneal endothelium although the net fluid pump rates were less than those measurable with a bicarbonate-buffered, CO2-equilibrated Ringer solution. Evaluation of the endothelia by scanning electron microscopy revealed no evidence of any acute toxic effect of the balanced salt solutions. Morphometric analyses of cell size and shape revealed a normal mosaic for endothelia exposed to commercial balanced salt solution for 5 h. The results further indicate that exogenous bicarbonate is not required for the net fluid pump function of the mammalian corneal endothelium.

Analyses of areas and shapes of cells on the corneal surface of the albino rabbit by scanning electron microscopy

The surface of 8 different corneal quadrants was assessed by scanning electron microscopy. Cells were identified by their electron reflex (light, medium, dark) and their areas, longest and shortest dimensions measured using a manual digitizer tablet/computer-interfaced system. Analyses of over 8200 cells show that while light cells are predominantly small (uncorrected mean area of 39.7 microns2), there can be light cells ten times larger than this. Medium reflex cells show a very wide range of area (uncorrected values ranging from 16 to 1257 microns2) while dark reflex cells show an even wider range (24 to 2218 microns2). Analysis of the longest to shortest dimensions (LS ratio) reveals light cells to be more elongate than medium cells while dark cells tend to be rounder.

Long-term effects of a single dose of ultraviolet-B on albino rabbit cornea--II. Deturgescence and fluid pump assessed in vitro

Both eyes of female albino rabbits (1.9 kg: 9-10 wk old) were exposed to a single dose of UV-B (300 +/- 9 nm; 0.125 J/cm2 total dose) between 13.30 and 15.00 h. At various time periods thereafter (every 12 h for 3 days, 6, 7, 14, 28, 42, 56, 112, 224 and 336 days post-irradiation), animals were sacrificed, samples of aqueous humor taken for analysis and stroma-endothelium preparations obtained from the corneas. Following such threshold irradiation, small increases in aqueous humor tonicity and protein levels were observed. The preparations were mounted in a specular microscope assembly (for measuring the rate and magnitude of corneal deturgescence) or between two half chambers (for measuring fluid pump) and equilibrated for 2 h with a CO2-equilibrated glucose-adenosine-glutathione-supplemented Ringer solution at 37 degrees C and a hydrostatic pressure of 20 cm H2O. After equilibration the stromal thickness showed large variation with large reductions in both the rate and amplitude of deturgescence function observed by 36 h. Large reductions in fluid pump activity were also observed by 36 h. The magnitude of the effects on fluid pump were somewhat greater than the effects on deturgescence. Both functions recovered to pre-irradiation levels by 112 days post-irradiation.

Physiological state of the rabbit cornea following 4 degrees C moist chamber storage

Eyes from female albino rabbits (1.9-2.3 kg) were enucleated immediately following euthanasia along with the lids and conjunctiva. The globes were moist chamber-stored (in a 4 degrees C refrigerator with the lids closed and the cornea facing downwards) for 12-500 hr. Central corneal thickness (by ultrasound) increased from 350 to approximately 650 microns within 72 hr but changed little thereafter. In the latter period, the relative fluid pressure of the globe (pneumatonography) dropped to less than 10 mmHg, aqueous bicarbonate (tCO2) levels fell to less than 5 mM and anterior chamber fluid tonicity decreased progressively (especially after 24 hr storage) to reach values of around 200 mosmol l-1 by 7 days. Storma-endothelium preparations of the corneas, after 2 hr of in vitro equilibration with a bicarbonate-Ringer solution (supplemented with glucose, adenosine and glutathione) were evaluated for their ability to undergo deturgescence under silicone oil or to pump fluid against a hydrostatic pressure of 20 cmH2O. Corneal preparations from up to 7 days storage showed rapid (60 to 135 microns hr-1) and complete deturgescence (net change in thickness of 140-180 microns) that was maintained. Thereafter, the ability to show deturgescence declined to zero by 10 days. In marked contrast, endothelial fluid pump activity (of approximately 5 microliters hr-1) was manifest for only 36 hr after which time this function rapidly declined. Most corneas stored for periods longer than 48 hr exhibited a continuous leak (of -1 to -5 microliters hr-1). The results indicate that corneal deturgescence and endothelial fluid pump function are not necessarily coupled in vitro.