QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rahaman-Noronha, E. Articles by Wright, P. Search for Related Content PubMed PubMed Citation Articles by Rahaman-Noronha, E. Articles by Wright, P. Social Bookmarking                         What's this?

Journal of Experimental Biology, Vol 199, Issue 12 2713-2723, Copyright © 1996 by Company of Biologists

JOURNAL ARTICLES

Excretion and distribution of ammonia and the influence of boundary layer acidification in embryonic rainbow trout (Oncorhynchus mykiss)

E Rahaman-Noronha, M Donnell, C Pilley and P Wright

This study examined ammonia excretion by embryos of the rainbow trout (Oncorhynchus mykiss). The distribution of ammonia in relation to the H+ distribution and electrical potential was determined. The influence of the pH of the unstirred layer (USL) of water next to the external surface of the embryo was also assessed. Eyed-up embryos (35­40 days post-fertilization) were exposed to various external water conditions [pH 6.0, pH 10.0, 1.6 mmol l-1 NaCl, 0.0 mmol l-1 NaCl, 0.2 mmol l-1 NH4Cl, 2.5 mmol l-1 borax buffer (Na2B4O7.10H2O), 2.5 mmol l-1 Hepes, 0.1 mmol l-1 amiloride] for 30 min and ammonia excretion rates, ammonia concentration in the perivitelline fluid (PVF) and yolk, and the pH of the PVF, yolk and USL were measured. The rate of ammonia excretion was dependent, in part, on the partial pressure gradient of NH3 ( PNH3) from the PVF to the USL. Exposure to water of pH 6 increased, whereas NH4Cl or pH 10 exposure decreased, ammonia excretion rates. Elevated external Na+ levels also influenced the rate of ammonia excretion, but neither Na+-free water nor amiloride had any effect. The distribution of ammonia between the PVF and USL was dependent on the H+ distribution, but ammonia was distributed according to the electrical potential between the PVF and yolk. The USL was 0.32 pH units more acidic than the bulk water. Addition of buffer to the external water eliminated the acid USL and decreased ammonia excretion rates. We conclude that rainbow trout embryos excrete ammonia primarily as NH3, but when external Na+ levels are elevated, ammonia excretion may be independent of the PNH3 gradient. The acidic USL next to the chorion probably facilitates NH3 diffusion by maintaining the PNH3 through the conversion of NH3 to NH4+ upon entry into the USL.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				P. A. Essex-Fraser, S. L. Steele, N. J. Bernier, B. W. Murray, E. D. Stevens, and P. A. Wright Expression of Four Glutamine Synthetase Genes in the Early Stages of Development of Rainbow Trout (Oncorhynchus mykiss) in Relationship to Nitrogen Excretion J. Biol. Chem., May 27, 2005; 280(21): 20268 - 20273. [Abstract] [Full Text] [PDF]

				S. L. Steele, T. D. Chadwick, and P. A. Wright Ammonia detoxification and localization of urea cycle enzyme activity in embryos of the rainbow trout (Oncorhynchus mykiss) in relation to early tolerance to high environmental ammonia levels J. Exp. Biol., March 8, 2002; 204(12): 2145 - 2154. [Abstract] [Full Text] [PDF]

				C. Pilley and P. Wright The mechanisms of urea transport by early life stages of rainbow trout (Oncorhynchus mykiss) J. Exp. Biol., January 10, 2000; 203(20): 3199 - 3207. [Abstract]