Biological impacts of deep-sea carbon dioxide injection inferred from indices of physiological performance
Brad A. Seibel1,* and
Patrick J. Walsh2
1 Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss
Landing, CA 95039, USA
2 Marine Biology and Fisheries, National Institute of Environmental Health
Sciences, Marine and Freshwater Biomedical Science Center, Rosenstiel School
of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, University of
Miami, Miami, FL 33149, USA
View larger version (37K):
[in a new window]
|
Fig. 1. Schematic representation of an animal cell with the potential means of
regulating intracellular pH. (1), metabolic interconversion of acids and
bases. (2), buffering; HA represents a weak acid or base with a dissociation
constant in the physiological pH range. (3), transport of acids and bases
across cell membranes; carbonic anhydrase (CA) catalyzes the hydration of
CO2 to yield H2CO3, which then dissociates to
H+, HCO3-, and CO32-
(an abbreviated reaction is shown).
|
|
View larger version (13K):
[in a new window]
|
Fig. 2. A Davenport diagram, a graphical representation of the Henderson
Hasselbalch equation
(pH=pK+log[HCO3-]/[CO2]), demonstrating a
typical time course for compensation of extracellular (blood) acidosis.
Numbers between points represent time (h). Within 1 h of acidotic stress
(A—B), extracellular pH generally drops according to the buffering
capacity of the plasma. Over the next 12-24 h (B—C), bicarbonate
(y-axis; mmol l-1) is transported into the cell (or
protons out) in order to shift the equilibrium towards higher pH values. Upon
return to normal seawater CO2 tensions, there is a rapid increase
in pH (C—D), due again to passive reactions, followed by a slower
decompensation phase (D—A) leading to restoration of the original
acid—base status. Intracellular pH and bicarbonate concentrations
generally follow those in the extracellular fluid. See Cameron
(1989 ) for additional details
on acid—base balance.
|
|
View larger version (23K):
[in a new window]
|
Fig. 3. Metabolic rates (open blue circles) of fishes, cephalopods and crustaceans
as a function of minimum depth of occurrence (the depth below which 90% of the
individuals in a population are captured). Also shown is the capacity for
buffering of intracellular fluids in cephalopods (green circles) and the pH
sensitivity of respiratory proteins (red circles) in crustaceans, fishes and
cephalopods. Buffering capacity is measured in `slykes', here equal to the
quantity of base that must be added to a homogenate made from a 1 g sample of
muscle to titrate the pH from approximately 6 to 7. The Bohr coefficient is
the change in the log of respiratory oxygen affinity (P50;
defined as the oxygen partial pressure at which the respiratory protein is
half-saturated) over the change in pH. Bohr coefficients in these animal
groups are negative but are presented here as absolute values. The metabolic
rates are normalized to a common body mass of 10 g and measurement temperature
of 5°C using measured scaling coefficients and Q10
values where available or assuming a scaling coefficient of -0.25 and a
Q10 of 2. Data are from Childress and Seibel
(1998) and references therein.
Note that the y-axis is a log scale.
|
|
View larger version (15K):
[in a new window]
|
Fig. 4. Davenport diagram depicting passive buffering of intracellular pH (black
lines) in two cephalopod species. Similar increases in CO2 partial
pressure (in mmHg; 1 mmHg=133.3 Pa; represented by the blue isopleths and
numbers) will result in dramatically different changes in intracellular pH in
shallow-(Stenoteuthis oualaniensis) and deep-living (Japetella
heathi) cephalopods. Buffering data are from Seibel et al.
(1997).
|
|
View larger version (11K):
[in a new window]
|
Fig. 5. Percentage hemocyanin-oxygen saturation as a function of oxygen partial
pressure PO2 (mmHg; 1 mmHg=133.3 Pa) at pH 7.61
and 7.36 for Benthoctopus sp. (B. A. Seibel, unpublished data).
Ambient PO2 at capture depth (51 mmHg) is
indicated by an arrow. At ambient PO2, a drop
in blood pH of 0.3 units results in a 40% decrease in hemocyanin saturation.
All measurements were on dialyzed hemolymph at 5°C. Changes in pH were
achieved by varying CO2 concentrations, thus we cannot distinguish
between pH and CO2 effects on oxygen binding.
|
|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
© The Company of Biologists Ltd 2003
