Cutaneous ion exchange, and renal and extrarenal partitioning of acid and ammonia excretion in the larval tiger salamander, Ambystoma tigrinum, following ingestion of ammonium salts

Mechanisms of acid–base regulation in the African lungfishProtopterus annectens

“…In P. annectens, partitioning of the peak excretion of a base load into branchial/ cutaneous versus renal contributions revealed that 62% was eliminated into the water, and 38% into urine. Urine is similarly a minor route of net acid efflux during acid-base disturbances in fish (Kobayashi and Wood, 1980;Wood and Jackson, 1980;Cameron and Kormanik, 1982;Wood, 1991;Curtis and Wood, 1992) and aquatic amphibians (Stiffler and Bachoura, 1991;Stiffler, 1991;Talbot and Stiffler, 1992), with extra-renal excretion of acid-base equivalents playing a dominant role. In fish, up to 90% or more of acid-base movements occur across the branchial epithelium (Claiborne et al, 2002;Evans et al, 2005), whereas cutaneous acid-base excretion appears to predominate in aquatic amphibians (Stiffler, 1989).…”

“…Metabolic compensation consisting of negative net acid excretion (net base excretion) accompanied this respiratory compensation, with J net H + decreasing from 88.5±75.6 to -337.9±199.4·mol·H Worthley, 2001). Aquatic amphibians, however, parallel fish in utilizing extra-renal transfer of acid-base equivalents, in their case, via the skin (Stiffler and Bachoura, 1991;Stiffler, 1991;Talbot and Stiffler, 1992). Regardless of the tissue site, work on a variety of organisms suggests that similar cellular and molecular mechanisms of acid-base equivalent transfer are employed (for reviews, see Claiborne et al, 2002;Kirschner, 2004;Wall, 2005;Perry and Gilmour, 2006).…”