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CARDIAC, RENAL, AND RESPIRATORY INTEGRATION

Branchial membrane-associated carbonic anhydrase activity maintains CO₂ excretion in severely anemic dogfish

Bamfield Marine Station, Bamfield, British Columbia, Canada, V0R 1BO

Submitted 25 April 2003 ; accepted in final form 20 February 2004

Plasma CO₂ reactions in Pacific spiny dogfish (Squalus acanthias) have access to plasma and gill membrane-associated carbonic anhydrase (CA). Acute severe experimental anemia and selective CA inhibitors were used to investigate the role of extracellular CA in CO₂ excretion. Anemia was induced by blood withdrawal coupled to volume replacement with saline. Lowering hematocrit from 14.2 ± 0.4% (mean ± SE; N = 31) to 5.2 ± 0.1% (N = 31) had no significant impact on arterial or venous CO₂ tensions (Pa_CO2 and Pv_CO2, respectively) over the subsequent 2 h. PCO₂ was maintained despite the reduction in red cell number and a significant 32% increase in cardiac output (_b), both of which have been found to cause Pa_CO2 increases in teleost fish. By contrast, treatment of anemic dogfish with the CA inhibitors benzolamide (1.3 mg/kg) or F3500 (50 mg/kg), to selectively inhibit extracellular CA, elicited rapid and significant increases in Pa_CO2 of 0.68 ± 0.17 Torr (N = 6) and 0.53 ± 0.11 Torr (N = 7), respectively, by 30 min after treatment. These findings provide a functional context in which extracellular CA in dogfish contributes substantially to CO₂ excretion. Additionally, the apparent lack of effect of _b changes on PCO₂ suggests that, in contrast to teleost fish, CO₂ excretion in dogfish does not behave as a diffusion-limited system.

carbonic anhydrase; membrane-associated; benzolamide; acetazolamide; F3500; 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid

This article has been cited by other articles:

				K. M. Gilmour, M. Bayaa, L. Kenney, B. McNeill, and S. F. Perry Type IV carbonic anhydrase is present in the gills of spiny dogfish (Squalus acanthias) Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2007; 292(1): R556 - R567. [Abstract] [Full Text] [PDF]

				T. Georgalis, K. M. Gilmour, J. Yorston, and S. F. Perry Roles of cytosolic and membrane-bound carbonic anhydrase in renal control of acid-base balance in rainbow trout, Oncorhynchus mykiss Am J Physiol Renal Physiol, August 1, 2006; 291(2): F407 - F421. [Abstract] [Full Text] [PDF]