|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
First published online September 16, 2005
Journal of Experimental Biology 208, 3805-3815 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01780
An investigation of the role of carbonic anhydrase in aquatic and aerial gas transfer in the African lungfish Protopterus dolloi
1 Department of Biology, University of Ottawa, 150 Louis Pasteur, Ottawa, ON
K1N 6N5, Canada
2 Veterans Affairs Puget Sound Health Care System, 1660 South Columbian Way
Seattle, WA 98108, USA
3 Department of Natural Sciences, National Institute of Education, Nanyang
Technological University, Republic of Singapore
4 Department of Biological Sciences, National University of Singapore,
Republic of Singapore
* Author for correspondence (e-mail: sfperry{at}science.uottawa.ca)
Accepted 30 June 2005
Experiments were performed on bimodally breathing African lungfish Protopterus dolloi to examine the effects of inhibition of extracellular vs total (extracellular and intracellular) carbonic anhydrase (CA) activity on pulmonary and branchial/cutaneous gas transfer. In contrast to previous studies on Protopterus, which showed that the vast majority of CO2 is excreted into the water through the gill and/or skin whereas O2 uptake largely occurs via the lung, P. dolloi appeared to use the lung for the bulk of both O2 uptake (91.0±2.9%) and CO2 excretion (76.0±6.6%). In support of the lung as the more important site of CO2 transfer, aerial hypercapnia (PCO2=40 mmHg) caused a significant rise in partial pressure of arterial blood CO2 (PaCO2) whereas a similar degree of aquatic hypercapnia was without effect on PaCO2. Intravascular injection of low levels (1.2 mg kg-1) of the slowly permanent CA inhibitor, benzolamide, was without effect on red blood cell CA activity after 30 min, thus confirming its suitability as a short-term selective inhibitor of extracellular CA. Benzolamide treatment did not affect CO2 excretion, blood acid–base status or any other measured variable within the 30 min measurement period. Injection of the permeant CA inhibitor acetazolamide (30 mg kg-1) resulted in the complete inhibition of red cell CA activity within 10 min. However, CO2 excretion (measured for 2 h after injection) and arterial blood acid–base status (assessed for 24 h after injection) were unaffected by acetazolamide treatment. Intra-arterial injection of bovine CA (2 mg kg-1) caused a significant increase in overall CO2 excretion (from 0.41±0.03 to 0.58±0.03 mmol kg-1 h-1) and an increase in air breathing frequency (from 19.0±1.3 to 24.7±1.8 breaths min-1) that was accompanied by a slight, but significant, reduction in PaCO2 (from 21.6±1.6 to 19.6±1.8 mmHg).
The findings of this study are significant because they (i) demonstrate that, unlike in other species of African lungfish that have been examined, the gill/skin is not the major route of CO2 excretion in P. dolloi, and (ii) suggest that CO2 excretion in Protopterus may be less reliant on carbonic anhydrase than in most other fish species.
Key words: carbon dioxide excretion, oxygen uptake, gill, lung, acetazolamide, benzolamide, breathing, lungfish, Protopterus dolloi, carbonic anhydrase
This article has been cited by other articles:
|
|
 |
|
  K. M. Gilmour, R. M. Euverman, A. J. Esbaugh, L. Kenney, S. F. Chew, Y. K. Ip, and S. F. Perry Mechanisms of acid-base regulation in the African lungfish Protopterus annectens J. Exp. Biol., June 1, 2007; 210(11): 1944 - 1959. [Abstract] [Full Text] [PDF]
|
|
