Organic Ions as Modulators of Respiratory Pigment Function during Stress
Various organic ions determine the O₂ affinity of hemoglobin and hemocyanin. In the two pigment systems different ions are involved but both exhibit regulative mechanisms responsive to the severity of hypoxic stress. The depressing effect of 2,3-diphosphoglycerate, adenosine 5′-triphosphate (ATP), a...
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| Published in: | Physiological zoology 1990-03, Vol.63 (2), p.253-287 |
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| Main Author: | |
| Format: | Article |
| Language: | eng |
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| Online Access: | Get full text |
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| Summary: | Various organic ions determine the O₂ affinity of hemoglobin and hemocyanin. In the two pigment systems different ions are involved but both exhibit regulative mechanisms responsive to the severity of hypoxic stress. The depressing effect of 2,3-diphosphoglycerate, adenosine 5′-triphosphate (ATP), and guanosine 5′-triphosphate (GTP) often determines the O₂ affinity of hemoglobin in nonstressed vertebrates and is important during hypoxia, when organic phosphate concentration decreases. In crustaceans, hypoxia promotes increased uric acid and L-lactate blood concentrations, which increase the O₂ affinity of hemocyanin. As with phosphates and hemoglobin, lactate and urate contribute to the O₂ affinity of hemocyanin in nonstressed animals. Membrane receptors of erythrocytes from many vertebrates are stimulated by epinephrine. This stimulation results in a steady intracellular pH despite an extracellular acidosis. A constant intracellular pH prevents a decrease in hemoglobin O₂ affinity and often in O₂ content. The β-adrenergic effect is mediated by membrane transduction mechanisms which may involve the phosphorylation of membrane ion exchangers. Hemoglobin itself may have a direct effect on the activity of the ion exchangers, depending on the oxygenation state of the pigment. Hemocyanin is an extracellular protein, but there is evidence for a direct effect of dopamine that may increase hemocyanin O₂ affinity during severe or sudden shortfalls in O₂ supply, with the same result as epinephrine stimulation of the hemoglobin O₂-transport system. In both hemoglobin and hemocyanin systems different types of hypoxic stress are met by a progressive involvement of organic modulators which, while very different in detail, have the same general effect of optimizing O₂ delivery. |
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| ISSN: | 0031-935X 1937-4267 |