Carbonic anhydrase (CA) is absent in the plasma of vertebrates. In vitro, CA in fish
plasma will short-circuit the effect of catecholamines on the increase in red blood cell
(RBC) pH and volume, both of which increase the hemoglobin affinity for O₂. CA was
infused into trout for a period of 6h during which the animal was submitted to deep
hypoxia (PO₂= 30-35 torr) and during recovery after exhaustive exercise. During hypoxia,
O₂ content, lactate, catecholamines, hematocrit, hemoglobin and pHi were similar to the
saline infused control group. On the other hand, cell volume was significantly higher and
PHe, total CO₂ and organic phosphates were significantly lower than the control group.
The concentration of CA was not high enough to completely short-circuit the increase in
pHi and RBC volume caused by catecholamines. The lower pH in the CA infused animals
could enhance the activity of the Na+/H+ pump which would keep the NTP low. CA in
plasma, during hypoxia, did not cause the expected reduction in blood oxygen content but
did have a marked effect on plasma total CO₂. During the recovery period of exhaustive
exercise, lactate, catecholamines, hematocrit, hemoglobin, MCHC, PO₂, HbO₂, and pHi were
similar to the saline infused animals. Total CO₂ and PHe were significantly higher in the
CA infused fish than in the saline infused ones. CA infusion, in this case, probably caused
acid retention in the muscle. Acid efflux from the muscle would decrease pH or if the acid
was excreted at the gills, bicarbonate would be titrated and the stores would be lower than
in control animals. CA activity available to plasma would mean greater fluctuation of
plasma pH, at least in hypoxic conditions, and red blood cell pH in general. pH is a balance between acid loading at the muscle and acid excretion at the gills or the kidneys,
we cannot distinguish between a decrease and an increase of one of the two which resulted
in a decrease of plasma pH. Fish have a large Haldane effect and HCO₃ flux through the
red cell ensures that the protons are excreted as CO₂ and cannot bind again to hemoglobin.
The absence of CA in the plasma ensures that HCO₃ flux through the red cell is
maintained.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/4934 |
| Date | 05 1900 |
| Creators | Lessard, Joanne |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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