Studies on the toxic effects of La(3+) to Tetrahymena thermophila by microcalorimetry

The toxic effects of La(3+) on Tetrahymena thermophila have been studied by microcalorimetry at 28 degrees C. The metabolic rate constant (r) and peak time were linked to the concentration of La(3+). The changes of metabolic rate constant indicated that low-concentration La(3+) (0-75 mg/L) had no significant effects on the metabolism of Tetrahymena cells but high-concentration La(3+) (100-175 mg/L) could inhibit their metabolism. From the results obtained by cell counting and fluorescence depolarization measurements, the inhibition of metabolism resulted from the decrease in cell number and the reduction in cell membrane fluidity. According to the results, it is clear that the metabolic mechanism of Tetrahymena cells has been changed with the addition of high-concentration La(3+). In addition, microcalorimetry of Tetrahymena could be a sensible, easy-to-use, and convenient method for monitoring the potential effects of rare earth elements on cells and the freshwater ecosystem