Respiratory and renal roles of carbonic anhydrase in gas exchange and acid-base regulation

Cytoplasmic carbonic anhydrase isozymes in rainbow troutOncorhynchus mykiss: comparative physiology and molecular evolution

“…Unlike TCAb, however, TCAc exhibits a widespread distribution among different tissues, with greatest expression occurring in the brain and gills, and lower expression in the liver, gut, white muscle and the anterior and posterior kidney. Presumably, TCAc has numerous physiological roles (Henry, 1996), similar to mammalian CA I and II (Chegwidden and Carter, 2000;Parkkila, 2000;Swenson, 2000). The finding that TCAc is present with TCAb in the rbcs of trout is in contrast to the prevailing belief that teleost rbcs express only one CA isozyme (Maren et al, 1980;Sanyal et al, 1982;Kim et al, 1983; reviewed by Henry and Heming, 1998), but is in accordance with a few studies that presented evidence for two isozymes (Girard and Istin, 1975;Carter et al, 1976).…”

“…In mammals, CA I A. J. Esbaugh and others Carbonic anhydrase in the gills of trout and CA II are found in the cytoplasm of the rbcs as well as many other tissues throughout the body (Chegwidden and Carter, 2000;Parkkila, 2000;Swenson, 2000). In contrast, the major trout rbc CA isozyme, TCAb, appears to be found only in the rbc (Figs·4 and 5).…”

Carbonic anhydrase and acid–base regulation in fish

“…The I, II, III, XIII gene cluster emerged in mammals (or in the tetrapod line -our present knowledge of nonmammalian CA isoforms is insufficient to pinpoint the divergence more accurately than fish versus mammals). CA II is the workhorse of this cluster, being a high activity isoform of near ubiquitous distribution (Chegwidden and Carter, 2000) that contributes to systemic acid-base regulation both as the main red blood cell (RBC) isoform underlying CO 2 excretion (reviewed by Geers and Gros, 2000;Henry and Swenson, 2000;Swenson, 2000) and as a key player in HCO 3 -reabsorption in the mammalian kidney, where it accounts for 95% of renal total CA activity (reviewed by Swenson, 2000;Schwartz, 2002;Purkerson and Schwartz, 2007). By contrast, and keeping in mind that the data on which to base phylogenetic analyses are very limited, fish seem to have retained the ancestral state of a single, high activity CA isoform until the appearance of the teleosts, where a whole genome duplication of the teleost common ancestor gave rise to two closely related cytosolic isoforms differing in tissue distribution and kinetic properties (Figs 2 and 3).…”

Mechanisms of acid–base regulation in the African lungfishProtopterus annectens

“…Increased pulmonary ventilation during a metabolic acidosis reduces arterial P CO 2, thereby raising arterial pH, while CO 2 retained via hypoventilation can compensate for a metabolic alkalosis. Such respiratory compensation is a mainstay of the strategy used by tetrapods to regulate acid-base disturbances (Heisler, 1986;Swenson, 2000;McNamara and Worthley, 2001). In water-breathing fish, on the other hand, respiratory compensation is of negligible importance and acid-base balance is restored metabolically (for reviews, see Goss et al, 1998;Claiborne et al, 2002;Hirose et al, 2003;Perry et al, 2003b;Evans et al, 2005;Perry and Gilmour, 2006).…”

“…Adjustment of renal acid secretion plays an important complementary role to the gills (Wood et al, 1999;Georgalis et al, 2006a) (for reviews, see Perry and Fryer, 1997;Perry et al, 2003b;Perry and Gilmour, 2006). Tetrapods also employ metabolic mechanisms to compensate for acid-base disturbances, with the kidney being the main regulatory site (Heisler, 1986;Swenson, 2000;McNamara and African lungfish Protopterus annectens utilized both respiratory and metabolic compensation to restore arterial pH to control levels following the imposition of a metabolic acidosis or alkalosis. Acid infusion (3·mmol·kg -1 NH 4 Cl) to lower arterial pH by 0.24 units increased both pulmonary (by 1.8-fold) and branchial (by 1.7-fold) ventilation frequencies significantly, contributing to 4.8-fold and 1.9-fold increases in, respectively, aerial and aquatic CO 2 excretion.…”