Geoscience Reference
In-Depth Information
Blood P CO 2 in kPa (μatm)
(A)
2.40
(23,690)
2.00
(19,740)
1.60
(15,790)
1.33
(13,130)
1.07
(10,560)
18
0.80
(7,900)
high P CO 2
fully compensated
15
12
0.53
(5,230)
high P CO 2
uncompensated
high CO 2 (in vivo)
9
0.27
(2,670)
6
control P CO 2
( in vivo )
NB
3
0.13
(1,280)
0
7.3
7.4
7.5
7.6
7.7
7.8
Blood pH NBS
(B)
control P CO 2 ( in vivo )
100
high P CO 2 ( in vivo )
13.3 kPa
~ arterial P O 2
1.7 kPa
~ venous P O 2
80
high P CO 2 uncompensated
60
40
control P CO 2 ( in vivo )
20
high P CO 2 ( in vivo )
high P CO 2 uncompensated
0
6.5
6.9
7.3
7.7
8.1
8.5
Blood pH NBS
Figure 8.4 Regulation of blood pH in the cephalopod Sepia offi cinalis. (A) pH-bicarbonate diagram, displaying blood bicarbonate (HCO 3 - ) concentration,
pH, and P CO 2 isobars (modii ed from Gutowska et al. 2010a). Under control conditions blood P CO 2 in cephalopods is typically 0.2 to 0.3 kPa (about 2000 to
3000 μatm) higher than ambient in order to maintain a diffusive l ux of respiratory CO 2 out of the organism. When seawater p CO 2 increases to ~0.6 kPa
(about 5900 μatm), blood P CO 2 increases to ~1 kPa (about 9900 μatm, thick black isobar). Such an increase to a high blood P CO 2 would lead to a blood pH
of ~7.3 if no active compensation occurred, such that blood pH follows the buffering capacity of the blood proteins (dashed buffering line). However,
S. offi cinalis actively modii es the carbonate system of its blood to stabilize pH at a higher value in vivo (~7.5) by means of HCO 3 - accumulation (equivalent
to net proton excretion, see Melzner et al. 2009a for further discussion). For full pH compensation, S. offi cinalis would have to increase blood HCO 3 - to more
than 15 mmol l -1 (top right). Blood pH regulation has large implications for the function of the extracellular respiratory pigment haemocyanin. (B) In vitro
blood haemocyanin oxygen-binding curves for S. offi cinalis at two different oxygen partial pressures that correspond to arterial and venous values recorded
in vivo (modii ed from Johansen et al . 1982 ; Zielinski et al. 2001 ; Gutowska et al. 2010a). Lines indicate saturation of the pigment under arterial and venous
conditions under control and high P CO 2 conditions (uncompensated and partially compensated as in vivo). On the arterial side, it appears that the partial pH
compensation observed in vivo is crucial for maintaining full oxygen saturation of haemocyanin in the gills. Uncompensated blood pH would lead to <80%
oxygen saturation under arterial conditions. As cephalopods are chronically oxygen limited (e.g. O'Dor and Webber 1991; Hochachka 1994 ; Pörtner 1994 ;
Finke et al. 1996), such a decrease in arterial haemocyanin saturation could signii cantly decrease i tness.
 
 
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