The Dependence of the Oxygen-Concentrating Mechanism of the Teleost Eye (Salmo gairdneri) on the Enzyme Carbonic Anhydrase

Microoxygen polarographic electrodes were constructed and used to measure oxygen tension (POO2) in the eyes of rainbow trout (Salmo gairdneri). The values obtained are compared with arterial blood and environmental water POO2 and indicate that there is an oxygen-concentrating mechanism in the eye supplying oxygen to the avascular retina. Anatomically similar retes suggest that the mechanism is similar to the one which exists in the swim bladder. Elimination of the arterial blood supply to the choroidal gland rete mirabile of the eye (through pseudobranchectomy) and the consequent lowering of ocular oxygen tensions implicate the choroidal gland as one of the major components of the oxygen-concentrating mechanism. After pseudobranchectomy the presence of ocular POO2 above that of arterial blood is indicative of a secondary structure in the eye capable of concentrating oxygen. Inhibition of carbonic anhydrase, using acetazolamide, is shown to result in complete suppression of the oxygen-concentrating mechanism. A hypothesis is advanced for the participation of retinal-choroidal and erythrocyte carbonic anhydrase in the oxygen-concentrating mechanism.

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Acid-Base Regulation Following Exhaustive Exercise: A Comparison Between Freshwaterand Sea Water-Adapted Rainbow Trout (Salmo Gairdneri)

Journal of Experimental Biology ◽

10.1242/jeb.141.1.407 ◽

1989 ◽

Vol 141 (1) ◽

pp. 407-418 ◽

Cited By ~ 2

Author(s):

Y. TANG ◽

D. G. McDONALD ◽

R. G. BOUTILIER

Keyword(s):

Rainbow Trout ◽

Sea Water ◽

Environmental Water ◽

Exhaustive Exercise ◽

Salmo Gairdneri ◽

Acid Base ◽

Genetic Stock ◽

Arterial Blood ◽

Blood Ph ◽

Counter Ions

Blood acid-base regulation following exhaustive exercise was investigated in freshwater- (FW) and seawater- (SW) adapted rainbow trout (Salmo gairdneri) of the same genetic stock. Following exhaustive exercise at 10°C, both FW and SW trout displayed a mixed respiratory and metabolic blood acidosis. However, in FW trout the acidosis was about double that of SW trout and arterial blood pH took twice as long to correct. These SW/FW differences were related to the relative amounts of net H+ equivalent excretion to the environmental water, SW trout excreting five times as much as FW trout. The greater H+ equivalent excretion in SW trout may be secondary to changes in the gills that accompany the adaptation from FW to SW. It may also be related to the higher concentrations of HCO3− as well as other exchangeable counter-ions (Na+ and Cl−) in the external medium in SW compared to FW.

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CO2 excretion and postcapillary pH equilibration in blood-perfused turtle lungs

Journal of Experimental Biology ◽

10.1242/jeb.202.8.965 ◽

1999 ◽

Vol 202 (8) ◽

pp. 965-975

Author(s):

E.K. Stabenau ◽

T.A. Heming

Keyword(s):

Carbonic Anhydrase ◽

Anion Exchange ◽

Cell Suspensions ◽

Red Cell ◽

Co2 Partial Pressure ◽

Arterial Blood ◽

Pass Perfusion ◽

Erythrocyte Carbonic Anhydrase ◽

Co2 Excretion

Turtles possess a significant postcapillary CO2 partial pressure (PCO2) disequilibrium between arterial blood and alveolar gas. There are several possible explanations for this blood disequilibrium including a slow rate of erythrocyte physiological anion shift (Cl-/HCO3- exchange) or inaccessibility of plasma HCO3- to red blood cell or pulmonary carbonic anhydrase. The present study characterized the contribution of erythrocyte anion exchange and pulmonary and erythrocyte carbonic anhydrase to CO2 excretion and, hence, to postcapillary CO2-HCO3--H+ equilibration in blood-perfused turtle (Pseudemys scripta) lungs. Turtle lungs perfused in situ with red cell suspensions containing inhibitors of erythrocyte anion exchange and/or pulmonary and red cell carbonic anhydrase produced significant postcapillary blood PCO2 and pH disequilibria, while no disequilibria were measured when lungs were perfused with control red cell suspensions. Erythrocyte anion exchange and pulmonary intravascular carbonic anhydrase contributed 11 % and 9 %, respectively, to CO2 excretion during single-pass perfusion, whereas red cell and pulmonary carbonic anhydrase contributed 32 % to the measured CO2 excretion. The lack of a measurable PCO2 disequilibrium during perfusion with control erythrocyte suspensions in this study suggests that alternative mechanisms may be responsible for the arterial-lung PCO2 disequilibrium measured during breathing or diving episodes in turtles.

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Short Circuiting of the Ocular Oxygen Concentrating Mechanism in the Teleost Salmo gairdneri Using Carbonic Anhydrase Inhibitors

The Journal of General Physiology ◽

10.1085/jgp.64.3.263 ◽

1974 ◽

Vol 64 (3) ◽

pp. 263-273 ◽

Cited By ~ 15

Author(s):

Michael B. Fairbanks ◽

J. Russell Hoffert ◽

Paul O. Fromm

Keyword(s):

Rainbow Trout ◽

Carbonic Anhydrase ◽

Red Blood Cells ◽

Oxygen Concentration ◽

Blood Cells ◽

Salmo Gairdneri ◽

Retinal Tissue ◽

Rete Mirabile ◽

Counter Current

Ocular oxygen concentration by the process of counter current multiplication in rainbow trout (Salmo gairdneri) was rapidly suppressed after intraperitoneal injections of the carbonic anhydrase inhibitor CL-11,366. The rapidity with which this drug acted suggested a short circuiting of the choroidal rete mirabile. A comparison was made between the time after injection of inhibitor at which oxygen concentrating ability was lost to the time after injection of inhibitor at which its presence in red blood cells, choroidal rete, pseudobranch, and retinal tissue was first noted. A scheme for the possible role of carbonic anhydrase from each of these tissues in the process of ocular oxygen concentration is given.

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