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Which came first, the breath or the lung?
Abstracts / Comparative Biochemistry and Physiology, PartB 126 (2000) S1-S108
WHICH CAME FIRST, THE BREATH OR THE LUNG? S.F.Perry institut fiir Zoologic, Universit~lt Bonn, Poppelsdorfer Scbloss, 53115 Bonn, G e r m a n y Lungs are charaetistic of the Cladistia (Polypterus and Erpetoichthys), of lungfish and of tetrapods. These paired structures are ventral derivatives of the pharynx posterior to the gills. Their respiratory blood supply is from the sixth branchial artery and the venous outflow enters the heart separately from systemic and portal blood. The swimbladder is employed in breathing in the gar, the bowfin and in basal teleosts. The unpaired respiratory swimbladder, arrises dorsally from the posterior pharynx. Its respiratory arterial blood supply is homologous to that of the long, but the vein drains to the cardinal veins, and separate intercardiac channels for oxygenated and deoxygenated blood are lacking. In spite of recent evidence showing similar ventilatory mechanisms in the actinopterygian lineage (including Actinistia), which are distinct from those of lungfish and tetrapods, the separate origin of longs and swimbladder, and of the air-breathing habit have not been demonstrated. On the contrary, recent studies on the isolated brainstem preparation of the gar show a pattern of efferent activity correlated with glottal closure that is remarkably similar to that seen in the isolated brainstem of frogs and tadpoles. Given the complete lack of evidence for gas-filled organs in chondrichthyans and the isolated position of piacoderms, for which buoyancy organs of uncc~in homology have been demonstrated, it is likely that air breathing arose in early bony fish before the differentiation of lung and swimbladder. The primitive air-breathing organ may have been the gill pouches or even the modified gills themselves, served by the sixth branchial artery. Further development of the dorsal part led to the (respiratccy) swimbladder, whereas the paired veotral parts evolved into lungs. Pulmonary surfactant could have evolved from secretions of the gills or ofthebuccal lining to prevent a~esion of surfaces on expiration.
GAS SECRETION IN FISHES: APPARENT PK VALUES FOR ACID-INDUCED 02 AND CO2 RELEASE FROM RED BLOOD CELLS D. Petzhold, N. Heisler, and M. Berenbrink Dept. Animal Physiology, H u m b o l d t Universittit zu Berlin, Berlin, G e r m a n y In vertebrates, gas secretion uecurrs in gas bladder and retina of fishes, owing mainly to the Root effect, £ e. release of 02 from haemoglobin by local acidification. The resulting elevation of Po2 is enhanced by vascular counterctarent exchange systems, the respective retia mirabilia (I). Simultaneous to the release of 02, acidification results in production of C02 from HCO~, which will similarly be concentrated by the countercurrent-exchange rete. The function of the gas bladder depends primarily on the release of 02, hut is little affected by the additional C02. In contrast, in the poorly vascularized fish retina, which relies critically on quantitative release of oxygen (2), the concomitant release of C02 may affect retinal function by resulting in extreme Pco2s (3). This factor may gain particular impurimtce in fish hinging on ocular gas secretion but lacking a gas bladder secretory system, such as the rainbow trout, Oncorhynchus mykiss. Accordingly, this species was adopted in order to investigate the effect of fixed-acid addition on differential 02 and C02 release from erythrocytes. Erythrocytes supended in physiological saline and equilibrated at 15°C at pH 8.10 ± 0.03, Pco2 2.2 ± 0.1 mmHg and Po2 94.9 mmHg were titrated in a closed system to simulate various conditions at the enlrance to the choroid rete mirabile. Decreasing extracellular and inWacellular pH by stepwise addition of hydrochloric acid caused an increase in cellular water content as expected for passive proton distribution across the membrane. In consequence of bicarbonate titration Pco2 gradually increased, with an apparent exWacellular p/~ value of 6.64. Contrasting the production of C02, acidinduced release of 02 v/a Root effect was distinctly sigmoidal with an apparent extracellular pKa value of 7.61. Adding the beta-adrenergic agonist isoproterenol (10.5 mmol r t) reduced the apparent extracellular pK, values for 02 and C02 release by 0.24 and 0.09, respectively. These data indicate that the ratio of oxygen and carbon dioxide release in rainbow trout e~fihrocytes can effectively be modulated by beta-adrenergic agonists and the degree of acidification, a mechanism possibly utilized also in vivo to protect retinal tissues from extensively high Pco2. (1) Pelster, B. and Randall, D. J. (1998). Fish Physiology 17, 113-139. Academic Press, San Diego. (2) Former et al. (1973). Comp. Biochem. Physiol. 46A, 559-567. (3) Wittenberg, J. B. and Haedrich, R. L. (1974). Biol. Bull. 146, 137-156.
$77
WHICH CAME FIRST, THE BREATH OR THE LUNG? S.F.Perry institut fiir Zoologic, Universit~lt Bonn, Poppelsdorfer Scbloss, 53115 Bonn, G e r m a n y Lungs are charaetistic of the Cladistia (Polypterus and Erpetoichthys), of lungfish and of tetrapods. These paired structures are ventral derivatives of the pharynx posterior to the gills. Their respiratory blood supply is from the sixth branchial artery and the venous outflow enters the heart separately from systemic and portal blood. The swimbladder is employed in breathing in the gar, the bowfin and in basal teleosts. The unpaired respiratory swimbladder, arrises dorsally from the posterior pharynx. Its respiratory arterial blood supply is homologous to that of the long, but the vein drains to the cardinal veins, and separate intercardiac channels for oxygenated and deoxygenated blood are lacking. In spite of recent evidence showing similar ventilatory mechanisms in the actinopterygian lineage (including Actinistia), which are distinct from those of lungfish and tetrapods, the separate origin of longs and swimbladder, and of the air-breathing habit have not been demonstrated. On the contrary, recent studies on the isolated brainstem preparation of the gar show a pattern of efferent activity correlated with glottal closure that is remarkably similar to that seen in the isolated brainstem of frogs and tadpoles. Given the complete lack of evidence for gas-filled organs in chondrichthyans and the isolated position of piacoderms, for which buoyancy organs of uncc~in homology have been demonstrated, it is likely that air breathing arose in early bony fish before the differentiation of lung and swimbladder. The primitive air-breathing organ may have been the gill pouches or even the modified gills themselves, served by the sixth branchial artery. Further development of the dorsal part led to the (respiratccy) swimbladder, whereas the paired veotral parts evolved into lungs. Pulmonary surfactant could have evolved from secretions of the gills or ofthebuccal lining to prevent a~esion of surfaces on expiration.
GAS SECRETION IN FISHES: APPARENT PK VALUES FOR ACID-INDUCED 02 AND CO2 RELEASE FROM RED BLOOD CELLS D. Petzhold, N. Heisler, and M. Berenbrink Dept. Animal Physiology, H u m b o l d t Universittit zu Berlin, Berlin, G e r m a n y In vertebrates, gas secretion uecurrs in gas bladder and retina of fishes, owing mainly to the Root effect, £ e. release of 02 from haemoglobin by local acidification. The resulting elevation of Po2 is enhanced by vascular counterctarent exchange systems, the respective retia mirabilia (I). Simultaneous to the release of 02, acidification results in production of C02 from HCO~, which will similarly be concentrated by the countercurrent-exchange rete. The function of the gas bladder depends primarily on the release of 02, hut is little affected by the additional C02. In contrast, in the poorly vascularized fish retina, which relies critically on quantitative release of oxygen (2), the concomitant release of C02 may affect retinal function by resulting in extreme Pco2s (3). This factor may gain particular impurimtce in fish hinging on ocular gas secretion but lacking a gas bladder secretory system, such as the rainbow trout, Oncorhynchus mykiss. Accordingly, this species was adopted in order to investigate the effect of fixed-acid addition on differential 02 and C02 release from erythrocytes. Erythrocytes supended in physiological saline and equilibrated at 15°C at pH 8.10 ± 0.03, Pco2 2.2 ± 0.1 mmHg and Po2 94.9 mmHg were titrated in a closed system to simulate various conditions at the enlrance to the choroid rete mirabile. Decreasing extracellular and inWacellular pH by stepwise addition of hydrochloric acid caused an increase in cellular water content as expected for passive proton distribution across the membrane. In consequence of bicarbonate titration Pco2 gradually increased, with an apparent exWacellular p/~ value of 6.64. Contrasting the production of C02, acidinduced release of 02 v/a Root effect was distinctly sigmoidal with an apparent extracellular pKa value of 7.61. Adding the beta-adrenergic agonist isoproterenol (10.5 mmol r t) reduced the apparent extracellular pK, values for 02 and C02 release by 0.24 and 0.09, respectively. These data indicate that the ratio of oxygen and carbon dioxide release in rainbow trout e~fihrocytes can effectively be modulated by beta-adrenergic agonists and the degree of acidification, a mechanism possibly utilized also in vivo to protect retinal tissues from extensively high Pco2. (1) Pelster, B. and Randall, D. J. (1998). Fish Physiology 17, 113-139. Academic Press, San Diego. (2) Former et al. (1973). Comp. Biochem. Physiol. 46A, 559-567. (3) Wittenberg, J. B. and Haedrich, R. L. (1974). Biol. Bull. 146, 137-156.
$77