Olfactory sensitivity to changes in environmental [Ca(2+)] in the freshwater teleost Carassius auratus: an olfactory role for the Ca(2+)-sensing receptor?
2002
SUMMARY Olfactory sensitivity to changes in environmental Ca 2+ has been
demonstrated in two teleost species; a salmonid ( Oncorhynchus nerka )
and a marine/estuarine perciform ( Sparus aurata ). To assess whether
this phenomenon is restricted to species that normally experience large
fluctuations in external ion concentrations (e.g. moving from sea water to
fresh water) or is present in a much wider range of species, we investigated
olfactory Ca 2+ sensitivity in the goldfish ( Carassius
auratus ), which is a stenohaline, non-migratory freshwater cyprinid.
Extracellular recording from the olfactory bulb in vivo by
electroencephalogram (EEG) demonstrated that the olfactory system is acutely
sensitive to changes in external Ca 2+ within the range that this
species is likely to encounter in the wild (0.05-3 mmol l -1 ). The
olfactory system responded to increases in external calcium with increasing
bulbar activity in a manner that fitted a conventional Hill plot with an
apparent EC 50 of 0.9±0.3 mmol l -1 (close to both
ambient and plasma free [Ca 2+ ]) and an apparent Hill coefficient of
1.1±0.3 (means ± S.E.M., N =6). Thresholds of detection
were below 50 μmol l -1 . Some olfactory sensitivity to changes in
external [Na + ] was also recorded, but with a much higher threshold
of detection (3.7 mmol l -1 ). The olfactory system of goldfish was
much less sensitive to changes in [Mg 2+ ] and [K + ].
Preliminary data suggest that Ca 2+ and Mg 2+ are detected
by the same mechanism, although with a much higher affinity for
Ca 2+ . Olfactory sensitivity to Na + may warn freshwater
fish that they are reaching the limit of their osmotic tolerance when in an
estuarine environment. Olfaction of serine, a potent odorant in fish, was not
dependent on the presence of external Ca 2+ or Na + .
Finally, the teleost Ca 2+ -sensing receptor (Ca-SR) was shown to be
highly expressed in a subpopulation of olfactory receptor neurones by both
immunocytochemistry and in situ hybridisation. The olfactory
sensitivity to Ca 2+ (and Mg 2+ ) is therefore likely to be
mediated by the Ca-SR. We suggest that olfactory Ca 2+ sensitivity
is a widespread phenomenon in teleosts and may have an input into the
physiological mechanisms regulating internal calcium homeostasis.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
25
References
32
Citations
NaN
KQI