The disruption of Daphnia magna sodium metabolism by humic substances: Mechanism of action and effect of humic substance source

Chris N. Glover, Chris M. Wood

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

Abstract

Humic substances have important functions in aquatic systems. While these roles are primarily indirect, influencing the physicochemical environment, recent evidence suggests these materials may also have direct biological actions. This study investigated the mechanism by which humic substances perturb sodium metabolism in a freshwater invertebrate, the water flea Daphnia magna. Aldrich humic acid (AHA) stimulated the maximal rate of whole-body sodium influx (Jmax) when experimental pH was 6 and water calcium content was 0.5 mM. This effect persisted at pH 8 and 1 mM calcium but not at pH 8 in the absence of calcium. An indirect action of AHA on apical transporter activity was proposed to explain this effect. At pH 4 AHA promoted a linear sodium uptake kinetic relationship, attributed to altered membrane permeability due to enhanced membrane binding of humic substances at low pH. In contrast, a real-world natural organic matter sample had no consistent action on sodium influx, suggesting that impacts on sodium metabolism may be limited to commercially available humic materials. These findings question the applicability of commercially available humic substances for laboratory investigations and have significant implications for the study of environmental metal toxicity.

Original languageEnglish (US)
Pages (from-to)1005-1016
Number of pages12
JournalPhysiological and Biochemical Zoology
Volume78
Issue number6
DOIs
StatePublished - Nov 1 2005

ASJC Scopus subject areas

  • Physiology
  • Biochemistry
  • Animal Science and Zoology

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