Tetrahymena in Cytotoxicology: with special reference to effects of heavy metals and selected drugs.

For over forty years, Tetrahymena has been the organism of choice in a variety of assays. The extensive use of the ciliate as a test organism relates to the ease with which it grows in axenic cultures with a short generation time and, not least, to the comprehensive knowledge available on its biochemistry and morphology. The purpose of the present work has been to review the use of Tetrahymena in cytotoxicology. To cover all aspects of this field would expand the review beyond its limits, hence it has been confined to the effects of heavy metals (Cu, Zn, Co, Ni, Cd, Hg, Pb) and some selected drugs (chloramphenicol, methotrexate, cis-platin, chloroquine). Different strains of T. pyriformis have been used over the years in cytotoxicology. Some of the strains are now species and will be referred to by their new names; moreover, for uniformity, the test compounds will be given in molarity if not stated as such originally. In principle, addition of a test compound to the cultures is the only change to which the cells are subjected, provided that other growth factors are kept constant. The addition may, however, change the pH of the medium which, if unadjusted, may affect the cells unrelated to the action of the compound, a common "pitfall" in cytotoxicology. The importance of pH is discussed in relation to toxicity. Apart from specific actions of heavy metals and drugs, general responses of Tetrahymena to unfavourable growth conditions are emphasized, also in relation to the question of detoxication.