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First published online October 21, 2005
Journal of Experimental Biology 208, 4035-4047 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01874

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Oxygen delivery to the fish eye: Root effect as crucial factor for elevated retinal P_O2

W. Waser^* and N. Heisler

Department of Animal Physiology, Humboldt-Universität zu Berlin, 10115 Berlin, Germany

View larger version (98K): [in a new window]   Fig. 1. Microphotograph of trout retina section (PE+PRL, pigment epithelium and photoreceptor layer; OLM, outer limiting membrane; ONL, outer nuclear layer; OPL, outer plexiform layer; INL, inner nuclear layer; IPL, inner plexiform layer; GCL, ganglion cell layer; NFL, nerve fibre layer; ILM, inner limiting membrane). The trout retina is completely devoid of blood vessels. Numbers denote thickness ± S.D.(N=3) in µm of the respective layers. For GCL and NFL the combined thickness of the two layers is given. Insert: Microphotographs of eel retina as an example of a teleost retina with intraretinal vascularization. Large blood vessels visible on ILM reach into the retina to OLM. Bars, 100 µm, 50 µm (insert).

View larger version (16K): [in a new window]   Fig. 2. Thickness of retina and individual layers. (A) Thickness of the whole retina (Bruch's membrane to ILM). (B,C) Thickness of individual layers (B): PE+PRL, ONL, OPL; (C): INL, IPL, GCL+NFL. Position of measurement (x-axis) is presented as relative; the axis spans the entire semicircular arc formed by the retina (for abbreviations, see Fig. 1).

View larger version (16K): [in a new window]   Fig. 3. Selection of PO2 profiles in the trout retina. Position at 0 µm corresponds to the inner surface of the retina (ILM). Shaded areas depict range of lowest to highest PO2. Electrodes were advanced into (closed symbols) and withdrawn out of (open symbols) the retina, resulting in duplicate recording lines. The red horizontal line indicates arterial PO2 (1 mmHg=133.3 Pa).

View larger version (16K): [in a new window]   Fig. 4. Root-effect of red blood cell (RBC) suspensions. (A) Haemoglobin-bound oxygen concentration vs pH. pH values at `Root on' of 90%, 50% and 10% are indicated. RBC suspensions utilized for in vitro perfusion of isolated eyes: red circles (trout) and blue diamonds (human). Correlation coefficient of fitted line: r=0.962. (B) PO2 vs pH of anaerobically acidified samples of trout (red circles) and human (blue diamonds) RBC suspensions. The pH value at 50% Root-effect is indicated by broken lines. Correlation coefficients of fitted lines: r=0.949 (trout RBC samples) and r=0.055 (human RBC samples). Confidence intervals (95%) to the fitted sigmoidal curves are indicated by broken lines.

View larger version (14K): [in a new window]   Fig. 5. Time course of selected in vitro determination of intraocular PO2. Periods of perfusion with different RBC suspensions (Tr, trout; H, human; R, Ringer solution) are indicated by grey bars above the graph. Initial increase in PO2 was due to the advance of the microelectrode into the retina.