Annika Salama

5 - Oxygen Transport in Fish

This chapter discusses the different aspects of oxygen transport in fishes. The oxygen-binding properties of hemoglobin can be described using the oxygen equilibrium curve, which relates the prevailing oxygen tension to the oxygen saturation of hemoglobin. Oxygen transport to tissues can be affected both by changes in the arterial oxygen tension and by changes in the oxygen affinity of hemoglobin. The oxygen affinity of hemoglobin within the erythrocyte is a function of the intrinsic oxygen affinity of hemoglobin, the sensitivity of hemoglobin-oxygen affinity to heterotrophic ligands, the concentration of hemoglobin within the cell, and the concentration of heterotrophic ligands within the erythrocyte. The volume of erythrocytes is influenced by the charge of organic phosphates and hemoglobin. It is found that if the negative charge of hemoglobin and organic phosphates decreases, either permeable cations must leave the cell or permeable anions enter the cell to maintain electroneutrality. It is suggested that a reduction of volume at high oxygen tensions could facilitate the entrance of erythrocytes to capillaries if the surface-to-volume ratio of the erythrocyte is the major determinant of the overall deformability of the erythrocyte.

Species differences in the adrenergic responses of fish red cells: studies on whitefish, pikeperch, trout and carp.

The occurrence and pH dependence (pHe 7–8) of the adrenergic red cell responses of two salmonids, trout and whitefish, and a percinid, pikeperch were studied. These are all species that live in well-oxygenated waters. The responses were compared to those of carp, which tolerates oxygen-deficient waters.The adrenergic responses of trout and whitefish red cells were pronounced. In these species red cell swelling, the accumulation of sodium and chloride in the cell, and the increase in red cell oxygen content at atmospheric oxygen tension were maximal at pH 7.3. In contrast, pikeperch red cells responded to β-adrenergic stimulation only at extracellular pH 7.1. In carp, the adrenergic response, occurring below extracellular pH 7.5, was small as compared to the two salmonids. In each case the onset of the adrenergic response coincided with the onset of the Root effect.The differences in the adrenergic responses between the two salmonids and pikeperch suggest that the occurrence of the adrenergic response is not directly related to the environmental oxygen requirements of the species, but may be linked to the activity pattern.

The role of cAMP in regulating the β-adrenergic response of rainbow trout (Oncorhynchus mykiss) red blood cells

The β-adrenergic response of teleost red blood cells (RBCs) enables the fish to maintain or even enhance the oxygen affinity of haemoglobin during various stress situations. The role of CAMP in the pronounced β-adrenergic response of hypoxic rainbow trout RBCs was studied. Rainbow trout RBCs were incubated with three different β-agonists (noradrenaline, adrenaline and isoproterenol, 10−9 - 10−4 M) at two oxygen tensions (PO2, 155 and 8 mmHg), and thereafter cAMP accumulation and cellular water content were measured.The cAMP concentration of non-stimulated trout RBCs was ca. 1200 nmol/kg dw. Of the three β-agonists used, isoproterenol was the most effective in formation of cAMP, followed by noradrenaline and adrenaline. Oxygen tension affected the accumulation of cAMP in two ways. At physiological catecholamine levels (1–100 nM) there was either no difference between normoxic and hypoxic cells or a slight increase in the normoxic ones. At high catecholamine concentrations the accumulation of cAMP was greater in the hypoxic than in the normoxic cells. Oxygen tension also affected the magnitude of cell swelling but had no effect on the catecholamine concentrations causing half-maximal swelling (EC50-values). The results indicate that, at physiological catecholamine levels, the β-adrenergic response of rainbow trout RBCs is mainly regulated on the level of the Na+/H+ exchange.

Adaptations in the capacity of ionic and osmotic regulation in young Baltic salmon (Salmo Salar L.) in brackish water

Abstract 1. 1. One-year-old Baltic salmon were reared in fresh water (FW) and brackish water (BW, salinity 6 ppt) for their second year of life. 2. 2. After 2.5 months of adaptation, the plasma ionic and osmotic concentrations of FW and BW fish responded similarly to 48 hr exposure to deionized water (DW), FW, BW and artificial sea-water (SW, salinity 17 ppt), but there were some differences in the intracellular ion and erythrocytic haemoglobin and ATP concentrations. 3. 3. After 10 months of adaptation, the ionic and osmotic balance of SW-exposed fish was similar in FW and BW fish, but the BW fish lost more ions in DW exposure than the FW ones. 4. 4. The results indicate that the overall capacity of young salmon to regulate hyper and hypoosmotically is only slightly affected by adaptation to BW. The differences in intracellular ion and ATP concentrations may partly be related to differences in the respiratory metabolism.

β‐Adrenergic Stimulation of Volume‐Sensitive Chloride Transport in Lamprey Erythrocytes

We measured the effects of a &bgr;‐adrenergic agonist, isoproterenol, on chloride transport and volume regulation of lamprey (Lampetra fluviatilis) erythrocytes in isotonic (288 mosm L−1) and hypotonic (192 mosm L−1) medium. Isoproterenol at a high concentration (10−5 M) did not influence chloride transport in isotonic medium but markedly increased chloride fluxes in hypotonic conditions: unidirectional flux increased from 100 mmol kg dcw−1 h−1 in the absence to 350 mmol kg dcw−1 h−1 ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

The linkage between Na+ uptake and ammonia excretion in rainbow trout: kinetic analysis, the effects of (NH4)2SO4 and NH4HCO3 infusion and the influence of gill boundary layer pH

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Respiratory Effects of Environmental Acidification in Perch (Perca fluviatilis) and Rainbow Trout (Salmo gairdneri)

\end{document} cell weight) in the presence of isoproterenol. Simultaneously, the half‐time for volume recovery decreased from 27 to 9 min. Isoproterenol caused an increase in cellular cyclic AMP (cAMP) concentration. The stimulation of chloride transport in hypotonic conditions could be induced by application of the permeable cAMP analogue, 8‐bromo‐cyclicAMP, suggesting that the effect of &bgr;‐adrenergic stimulation on chloride transport occurs downstream of cAMP production. As isoproterenol did not affect unidirectional rubidium fluxes in hypotonic conditions, the transport pathway influenced by &bgr;‐adrenergic stimulation is most likely the swelling‐activated chloride channel. Because the &bgr;‐adrenergic agonist only influenced the transport in hypotonic conditions despite the fact that cAMP concentration also increased in isotonic conditions, the activation may involve a volume‐dependent conformational change in the chloride channel.