Investigating a potential mechanism of Cd resistance in Chironomus riparius larvae using kinetic analysis of calcium and cadmium uptake

Patricia L. Gillis, Chris M. Wood

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The uptake kinetics of waterborne Ca and Cd, both independently and in combination, were examined in C. riparius larvae, which are extremely Cd tolerant. Larvae exposed to Ca (100-2500 μmol L-1), exhibited classic Michaelis-Menten saturation kinetics for Ca influx, measured using 45Ca as a radio-tracer. The maximum rate of Ca influx (JmaxCa) was 0.39 μmol g-1 h-1, and the Ca concentration where the carrier reached half saturation (KMCa) was 289 μmol L-1. Cd influx was measured using 109Cd as a radio-tracer in larvae exposed to Cd (0-1400 μmol L-1) while the Ca concentration was set to the KMCa. This revealed a JmaxCd (2.26 μmol g-1 h-1) which was nearly 6-fold higher that of Ca. This unusually high capacity for Cd uptake is in accordance with the huge tissue Cd burdens that chironomid larvae are able to accumulate during high level exposures. The apparent KMCd (1133 μmol Cd L-1), when recalculated to account for the background Ca level, was still high (567 μmol Cd L-1), suggesting that this organism has a low affinity for Cd relative to most aquatic animals, indeed lower or comparable to its affinity for Ca. In consequence, even well above environmentally relevant Cd exposures, C. riparius does not accumulate Cd at the expense of Ca, thereby avoiding internal hypocalcaemia, in contrast to most other organisms which are much more sensitive to Cd. However, Ca influx was significantly reduced when 1200 μmol Cd L-1 was added to Ca exposures (96-2410 μmol L-1). Michaelis-Menten analysis revealed a similar JmaxCa in Cd-exposed and control larvae (i.e. exposed only to Ca), but that the apparent KMCa was many-fold higher in larvae which were simultaneously exposed to Ca and Cd. Conversely, increasing Ca concentrations (96-2410 μmol L-1) progressively inhibited Cd uptake from a Cd exposure concentration (1200 μmol L-1), providing additional support for a common transport system. These results suggest that the interaction of Cd and Ca in C. riparius is one of simple competitive interaction, and that the unusual Cd transport kinetics (low affinity, high capacity) relative to fairly standard Ca transport kinetics help explain the unusual tolerance that this organism has to acute Cd exposure.

Original languageEnglish
Pages (from-to)180-187
Number of pages8
JournalAquatic Toxicology
Volume89
Issue number3
DOIs
StatePublished - Sep 17 2008

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Chironomus riparius
Chironomidae
resistance mechanisms
Cadmium
Larva
cadmium
calcium
Calcium
larva
uptake mechanisms
kinetics
larvae
Radio
radio
tracer techniques
organisms
tracer
saturation
fold
hypocalcemia

Keywords

  • Cadmium
  • Calcium
  • Chironomid
  • Chironomus riparius
  • Metal accumulation
  • Metal tolerance
  • Michaelis-Menten
  • Uptake inhibition
  • Uptake kinetics

ASJC Scopus subject areas

  • Aquatic Science

Cite this

Investigating a potential mechanism of Cd resistance in Chironomus riparius larvae using kinetic analysis of calcium and cadmium uptake. / Gillis, Patricia L.; Wood, Chris M.

In: Aquatic Toxicology, Vol. 89, No. 3, 17.09.2008, p. 180-187.

Research output: Contribution to journalArticle

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N2 - The uptake kinetics of waterborne Ca and Cd, both independently and in combination, were examined in C. riparius larvae, which are extremely Cd tolerant. Larvae exposed to Ca (100-2500 μmol L-1), exhibited classic Michaelis-Menten saturation kinetics for Ca influx, measured using 45Ca as a radio-tracer. The maximum rate of Ca influx (JmaxCa) was 0.39 μmol g-1 h-1, and the Ca concentration where the carrier reached half saturation (KMCa) was 289 μmol L-1. Cd influx was measured using 109Cd as a radio-tracer in larvae exposed to Cd (0-1400 μmol L-1) while the Ca concentration was set to the KMCa. This revealed a JmaxCd (2.26 μmol g-1 h-1) which was nearly 6-fold higher that of Ca. This unusually high capacity for Cd uptake is in accordance with the huge tissue Cd burdens that chironomid larvae are able to accumulate during high level exposures. The apparent KMCd (1133 μmol Cd L-1), when recalculated to account for the background Ca level, was still high (567 μmol Cd L-1), suggesting that this organism has a low affinity for Cd relative to most aquatic animals, indeed lower or comparable to its affinity for Ca. In consequence, even well above environmentally relevant Cd exposures, C. riparius does not accumulate Cd at the expense of Ca, thereby avoiding internal hypocalcaemia, in contrast to most other organisms which are much more sensitive to Cd. However, Ca influx was significantly reduced when 1200 μmol Cd L-1 was added to Ca exposures (96-2410 μmol L-1). Michaelis-Menten analysis revealed a similar JmaxCa in Cd-exposed and control larvae (i.e. exposed only to Ca), but that the apparent KMCa was many-fold higher in larvae which were simultaneously exposed to Ca and Cd. Conversely, increasing Ca concentrations (96-2410 μmol L-1) progressively inhibited Cd uptake from a Cd exposure concentration (1200 μmol L-1), providing additional support for a common transport system. These results suggest that the interaction of Cd and Ca in C. riparius is one of simple competitive interaction, and that the unusual Cd transport kinetics (low affinity, high capacity) relative to fairly standard Ca transport kinetics help explain the unusual tolerance that this organism has to acute Cd exposure.

AB - The uptake kinetics of waterborne Ca and Cd, both independently and in combination, were examined in C. riparius larvae, which are extremely Cd tolerant. Larvae exposed to Ca (100-2500 μmol L-1), exhibited classic Michaelis-Menten saturation kinetics for Ca influx, measured using 45Ca as a radio-tracer. The maximum rate of Ca influx (JmaxCa) was 0.39 μmol g-1 h-1, and the Ca concentration where the carrier reached half saturation (KMCa) was 289 μmol L-1. Cd influx was measured using 109Cd as a radio-tracer in larvae exposed to Cd (0-1400 μmol L-1) while the Ca concentration was set to the KMCa. This revealed a JmaxCd (2.26 μmol g-1 h-1) which was nearly 6-fold higher that of Ca. This unusually high capacity for Cd uptake is in accordance with the huge tissue Cd burdens that chironomid larvae are able to accumulate during high level exposures. The apparent KMCd (1133 μmol Cd L-1), when recalculated to account for the background Ca level, was still high (567 μmol Cd L-1), suggesting that this organism has a low affinity for Cd relative to most aquatic animals, indeed lower or comparable to its affinity for Ca. In consequence, even well above environmentally relevant Cd exposures, C. riparius does not accumulate Cd at the expense of Ca, thereby avoiding internal hypocalcaemia, in contrast to most other organisms which are much more sensitive to Cd. However, Ca influx was significantly reduced when 1200 μmol Cd L-1 was added to Ca exposures (96-2410 μmol L-1). Michaelis-Menten analysis revealed a similar JmaxCa in Cd-exposed and control larvae (i.e. exposed only to Ca), but that the apparent KMCa was many-fold higher in larvae which were simultaneously exposed to Ca and Cd. Conversely, increasing Ca concentrations (96-2410 μmol L-1) progressively inhibited Cd uptake from a Cd exposure concentration (1200 μmol L-1), providing additional support for a common transport system. These results suggest that the interaction of Cd and Ca in C. riparius is one of simple competitive interaction, and that the unusual Cd transport kinetics (low affinity, high capacity) relative to fairly standard Ca transport kinetics help explain the unusual tolerance that this organism has to acute Cd exposure.

KW - Cadmium

KW - Calcium

KW - Chironomid

KW - Chironomus riparius

KW - Metal accumulation

KW - Metal tolerance

KW - Michaelis-Menten

KW - Uptake inhibition

KW - Uptake kinetics

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