Temperature and the oxygen-hemoglobin dissociation curve of the harbor seal, Phoca vitulina

SUMMARYThe management and depletion of O 2 stores underlie the aerobic dive capacities of marine mammals. The California sea lion (Zalophus californianus) presumably optimizes O 2 store management during all dives, but approaches its physiological limits during deep dives to greater than 300m depth. Blood O 2 comprises the largest component of total body O 2 stores in adult sea lions. Therefore, we investigated venous blood O 2 depletion during dives of California sea lions during maternal foraging trips to sea by: (1) recording venous partial pressure of O 2 (P O2 ) profiles during dives, (2) characterizing the O 2 -hemoglobin (Hb) dissociation curve of sea lion Hb and (3) converting the P O2 profiles into percent Hb saturation (S O2 ) profiles using the dissociation curve. The O 2 -Hb dissociation curve was typical of other pinnipeds (P 50 =28±2mmHg at pH7.4). In 43% of dives, initial venous S O2 values were greater than 78% (estimated resting venous S O2 ), indicative of arterialization of venous blood. Blood O 2 was far from depleted during routine shallow dives, with minimum venous S O2 values routinely greater than 50%. However, in deep dives greater than 4min in duration, venous S O2 reached minimum values below 5% prior to the end of the dive, but then increased during the last 30-60s of ascent. These deep dive profiles were consistent with transient venous blood O 2 depletion followed by partial restoration of venous O 2 through pulmonary gas exchange and peripheral blood flow during ascent. These differences in venous O 2 profiles between shallow and deep dives of sea lions reflect distinct strategies of O 2 store management and suggest that underlying cardiovascular responses will also differ. Supplementary material available online at

Section: Discussion O 2 -Hb Dissociation Curvesupporting

confidence: 53%

Insights from venous oxygen profiles: oxygen utilization and management in diving California sea lions

McDonald

Ponganis

2013

“…The magnitude of the Bohr effect was expected to be similar to those in other birds and penguins (-0.4 to -0.6) (Lenfant et al, 1969b). A similar range of Bohr effects, which should favor O 2 unloading to the tissues, has also been observed in a variety of marine mammals (Lenfant et al, 1970;Qvist et al, 1981;Willford et al, 1990). An accurate determination of the Bohr effect in emperor penguin whole blood also allows refinement of the estimation of S O2 from P O2 profiles since P CO2 and pH data are available at various points in dives of this species Ponganis et al, 2007).…”

Section: Introductionsupporting

confidence: 59%

“…This is justified as, with the exception of disease, the structure of hemoglobin varies among species, not individuals of a species. The Bohr coefficient was derived from linear regression of the log P 50 on pH (each point averaged from all data of all birds for pH 7.5, 7.4, 7.3 and 7.2) (Nicol, 1991;Willford et al, 1990). In addition, the fixed acid Bohr effect was determined by titrating with HCl to pH 7.4, 7.3 and 7.2 while P CO2 was maintained at the level required for the standard pH 7.5 curve in that penguin (Willford et al, 1990).…”

Section: O 2 -Hb Dissociation Curve Characterizationmentioning

confidence: 99%

“…The Bohr coefficient was derived from linear regression of the log P 50 on pH (each point averaged from all data of all birds for pH 7.5, 7.4, 7.3 and 7.2) (Nicol, 1991;Willford et al, 1990). In addition, the fixed acid Bohr effect was determined by titrating with HCl to pH 7.4, 7.3 and 7.2 while P CO2 was maintained at the level required for the standard pH 7.5 curve in that penguin (Willford et al, 1990). The effect of lactic acid on the dissociation curve was also evaluated in whole blood by determining additional dissociation curve points after adding lactic acid (L6661, Sigma, St Louis, MO, USA) to the blood to a final concentration of 5 and 10 mmol l -1 (Nicol, 1991).…”

Section: O 2 -Hb Dissociation Curve Characterizationmentioning

confidence: 99%

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High-affinity hemoglobin and blood oxygen saturation in diving emperor penguins

Meir

Ponganis

2009

SUMMARYThe emperor penguin (Aptenodytes forsteri) thrives in the Antarctic underwater environment, diving to depths greater than 500 m and for durations longer than 23 min. To examine mechanisms underlying the exceptional diving ability of this species and further describe blood oxygen (O 2 ) transport and depletion while diving, we characterized the O 2 -hemoglobin (Hb) dissociation curve of the emperor penguin in whole blood. This allowed us to (1) investigate the biochemical adaptation of Hb in this species, and (2) address blood O 2 depletion during diving, by applying the dissociation curve to previously collected partial pressure of O 2 (P O2 ) profiles to estimate in vivo Hb saturation (S O2 ) changes during dives. This investigation revealed enhanced Hb-O 2 affinity (P 50 =28 mmHg, pH 7.5) in the emperor penguin, similar to high-altitude birds and other penguin species. This allows for increased O 2 at low blood P O2 levels during diving and more complete depletion of the respiratory O 2 store. S O2 profiles during diving demonstrated that arterial S O2 levels are maintained near 100% throughout much of the dive, not decreasing significantly until the final ascent phase. End-of-dive venous S O2 values were widely distributed and optimization of the venous blood O 2 store resulted from arterialization and near complete depletion of venous blood O 2 during longer dives. The estimated contribution of the blood O 2 store to diving metabolic rate was low and highly variable. This pattern is due, in part, to the influx of O 2 from the lungs into the blood during diving, and variable rates of tissue O 2 uptake.

“…The temperature coefficient of whole blood from bar-headed geese (0.028) corresponds to a shift of the P 50 of ~1.84mmHg°C -1 and is: (1) ~24-43% greater than that of other birds examined to date (Danzer and Cohn, 1967;Johansen et al, 1987;Maginniss et al, 1997;Pinshow et al, 1985), (2) 18-50% greater than that of mammals (Reeves et al, 1982;Smale and Butler, 1994;Willford et al, 1990), and (3) not dependent on pH (%CO 2 ) (Fig.1). The Bohr effect was slightly lower than previously reported for the barheaded goose (Black and Tenney, 1980), but similar to that of other birds and mammals Danzer and Cohn, 1967;Grispo et al, 2012;Lutz et al, 1973;Weber and Campbell, 2011), and was not temperature dependent.…”

Section: Discussionmentioning

confidence: 90%

High thermal sensitivity of blood enhances oxygen delivery in the high-flying bar-headed goose

Meir

Milsom

2013

SUMMARYThe bar-headed goose (Anser indicus) crosses the Himalaya twice a year at altitudes where oxygen (O 2 ) levels are less than half those at sea level and temperatures are below −20°C. Although it has been known for over three decades that the major hemoglobin (Hb) component of bar-headed geese has an increased affinity for O 2 , enhancing O 2 uptake, the effects of temperature and interactions between temperature and pH on bar-headed goose Hb-O 2 affinity have not previously been determined. An increase in breathing of the hypoxic and extremely cold air experienced by a bar-headed goose at altitude (due to the enhanced hypoxic ventilatory response in this species) could result in both reduced temperature and reduced levels of CO 2 at the blood-gas interface in the lungs, enhancing O 2 loading. In addition, given the strenuous nature of flapping flight, particularly in thin air, blood leaving the exercising muscle should be warm and acidotic, facilitating O 2 unloading. To explore the possibility that features of blood biochemistry in this species could further enhance O 2 delivery, we determined the P 50 (the partial pressure of O 2 at which Hb is 50% saturated) of whole blood from bar-headed geese under conditions of varying temperature and [CO 2 ]. We found that blood-O 2 affinity was highly temperature sensitive in bar-headed geese compared with other birds and mammals. Based on our analysis, temperature and pH effects acting on blood-O 2 affinity (cold alkalotic lungs and warm acidotic muscle) could increase O 2 delivery by twofold during sustained flapping flight at high altitudes compared with what would be delivered by blood at constant temperature and pH.