Short-term treatments (3h) designed to change the relative NH3 (ΔPNHNH3) and NH4+ (ΔNH4+) gradients and sodium transport (JNa) across the gills were employed to analyse the normal mechanism(s) of branchial ammonia excretion (JAmmnet) in trout acclimated to fresh water of pH ≃ 8.0. Control JAmmnet occurred in the absence of, or against, an apparent ΔPNH3 gradient, while ΔNH4+ was positive. Severe acid exposure (pH = 4.06) raised ΔPNH3 and ΔNH4+, abolished JNain, and reduced JAmmnet by 28%, while moderate acidity (pH = 6.64), which also elevated ΔPNH3 had no significant influence on JNain and JAmmnet. Severe alkaline exposure (pH = 9.54) raised ΔNH4+, reduced ΔPNH3 to a very negative value, and decreased JNain and JAmmnet by equimolar amounts, representing 55% and 80% of control levels respectively. Moderate alkalinity (pH = 8.69) had similar effects on ΔPNH3 and ΔNH4+, but reduced JNain and JAmmnet by only 25%. The sodium transport inhibitor amiloride (10−4moll−1 in the external water, pH ≃ 8.0) had very similar effects to pH = 4.06 on both JNain and JAmmnet but did not alter ΔPNH3 or ΔNH4+. The results discount the quantitative importance of NH4+ diffusion and favour a flexible combination of NH3 diffusion and Na+/NH4+ exchange as the major mechanisms of (JAmmnet). with the latter dominating under the particular control conditions of the present study.
An Analysis of Branchial Ammonia Excretion in the Freshwater Rainbow Trout: Effects of Environmental pH change and Sodium Uptake Blockade
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P. A. Wright, C. M. Wood; An Analysis of Branchial Ammonia Excretion in the Freshwater Rainbow Trout: Effects of Environmental pH change and Sodium Uptake Blockade. J Exp Biol 1 January 1985; 114 (1): 329–353. doi: https://doi.org/10.1242/jeb.114.1.329
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