Bioenergetic investigation of the effects of La(III) and Ca(II) on the metabolic activity of Tetrahymena thermophila BF5.

The heat flux of Tetrahymena thermophila BF5 during growth and the effects of La(3+) and Ca(2+) on them were investigated with microcalorimetry; simultaneously, morphological changes of T. thermophila were obtained by light microscope. La(3+) in low concentration (0-5.0 x 10(-4) mol/l) remarkably stimulated T. thermophila metabolism, but high dose of La(3+) (5.8-8.6 x 10(-4) mol/l) restrained it in a linear manner with IC(50) being 7.2 x 10(-4) mol/l. In contrast, low concentration of Ca(2+) did not manifest obvious stimulation on T. thermophila metabolism; moreover, the IC(50) of Ca(2+) was much higher than that of La(3+). Low concentration of La(3+) did not lead to changes in appearance of T. thermophila, but low dose of Ca(2+) clearly promoted the cell proliferation. In addition, the morphological changes of T. thermophila evoked by high concentrations of La(3+) and Ca(2+) were consistent with relevant microcalorimetric results. It is concluded that La and Ca influence T. thermophila via different pathways, and La represents toxic action rather than Ca analogy.