Air breathing by the purple shore crab, Hemigrapsus nudus (Dana). 3. Haemocyanin function in respiratory gas transport
The functional properties of the haemolymph and haemocyanin (Hc) of Hemigrapsus nudus were investigated with respect to the amphibious behaviour of this crab. The O sub(2) affinity of the Hc was decreased at higher temperature ( Delta H = -30 to -40 kJ/mol). Haemocyanin-O sub(2) affinity was sensiti...
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| Published in: | Physiological zoology 1996-07, Vol.69 (4), p.839-863 |
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| Main Authors: | , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | The functional properties of the haemolymph and haemocyanin (Hc) of Hemigrapsus nudus were investigated with respect to the amphibious behaviour of this crab. The O sub(2) affinity of the Hc was decreased at higher temperature ( Delta H = -30 to -40 kJ/mol). Haemocyanin-O sub(2) affinity was sensitive to pH (Bohr factor = -0.843 at 15 degree C) but essentially insensitive to L-lactate ( Delta log P sub(50)/ Delta log [lactate] = -0.053). The pH sensitivity of Hemigrapsus Hc was dependent on temperature (Bohr factor = -0.44 at 5 degree C, -0.90 at 25 degree C). Increasing CO sub(2) had no specific effect, nor was Hc-O sub(2) affinity increased by increasing levels of dopamine. Urate markedly increased the O sub(2) affinity of Hemigrapsus Hc ( Delta log P sub(50)/ Delta log [urate] = -0.203), and together with H super(+), it would seem to be the major organic effector of Hc-O sub(2) affinity. Increasing haemolymph Ca both potentiated Hc-O sub(2) affinity and decreased the magnitude of the Bohr shift. The potentiating effect was more pronounced at lower than normal Ca concentration, while Mg had little effect. The CO sub(2) capacitance of the haemolymph was more dependent on temperature than could be accounted for by the reduction in CO sub(2) solubility at higher temperature (CO sub(2) capacitance = 0.44-0.91 mmol/L/mmHg). Consistent with a relatively low haemolymph protein concentration, the nonbicarbonate buffer was low ( Delta [HCO sub(3) super(-)]/ Delta pH = -4.80), and thus changes in H super(+) concentration would promote large changes in pH and Hc-O sub(2) affinity. A Haldane effect was detected at 25 degree C. Relating these data to in vivo measurements showed that acid-base balance in Hemigrapsus emerging from 10 degree C water into 25 degree C air was likely managed separately from CO sub(2) excretion. In crabs breathing 10 degree C water, the Hc transported 50% of the used O sub(2), while in animals breathing 25 degree C air the amount of O sub(2) so transported rose to 85%. Emersion-induced acidosis initially promoted a large decrease in O sub(2) affinity, reduced oxygenation, and promoted a decrease in the arterial-venous O sub(2) content difference. However, a subsequent metabolic alkalosis and an elevation in haemolymph urate reestablished the transport role of the Hc. Thus the pH sensitivity, especially at high temperatures, and the effect of urate seem crucial to the amphibious behaviour of Hemigrapsus, whose modulator systems are quite unl |
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| ISSN: | 0031-935X 1937-4267 |