Ionic regulation in the Antarctic nematode Panagrolaimus davidi, measured using electron probe X-ray microanalysis.

The element composition of the pseudocoelomic fluid of the Antarctic nematode Panagrolaimus davidi was analysed by electron probe X-ray microanalysis after absorbing the fluid into Sephadex G-25 beads, and after producing calibration curves by analysing various concentrations of elements of interest absorbed into beads. The nematodes maintain higher concentrations of sodium and potassium in their pseudocoelomic fluid than in the external medium but lower concentrations of magnesium and calcium. When external concentrations of specific ions were elevated there was evidence for the regulation of internal concentrations of sodium, potassium, magnesium and chlorine. The time course of changes in response to exposure to elevated levels of KCl shows an increase in internal concentrations of potassium and chlorine up to 2 h after exposure, followed by a decline. This is consistent with a model of ionic regulation proposed for Caenorhabditis elegans which suggests that high concentrations of ionic osmolytes are replaced by compatible organic osmolytes.