P1.51 Wednesday, Jan. 4 Mechanisms of H+ and Ammonia Excretion in Exercising Blue Crabs, Callinectes sapidus BOOTH, C.E.*; HENRY, R.P.; Eastern Conn. State Univ.; Auburn Univ. email@example.com
David Towle made seminal contributions to our understanding of ion transport across the crustacean gill epithelium, including the discovery of an apical electrogenic 2Na+/H+ exchanger (2NHE). Gill ion transport (Na+/H+; Cl-/HCO3-) and ammonia excretion are thought to play key roles in the regulation of internal acid-base balance in crustaceans. However, our understanding of these processes is based largely on animals ionoregulating in FW or dilute SW. Little is known about gill mechanisms of acid-base regulation in SW-acclimated animals in which active Na+ and Cl- uptake are not required. We examined the mechanisms by which SW-acclimated blue crabs excrete H+ and ammonia during exercise. Net H+ excretion during exercise was reduced by 54% in Na+-free ASW and by 27% in HCO3--free ASW, and was abolished in ASW lacking both ions. Ammonia excretion during exercise was independent of ambient Na+, increased in HC03- -free ASW, and was depressed in alkaline ASW. These results implicate branchial Na+/H+ and Cl-/HCO3- exchange in the excretion of H ions, and NH3 diffusion as the major route for ammonia excretion during exercise. However, we are unable to determine if H+ excretion occurs by electroneutral Na+/H+ exchange, or via Towle's electrogenic 2NHE and parallel electrogenic H+ excretion.