title: Mode of action of ammonia and amine on rRNA synthesis in Xenopus laevis embryonic cells.
abstract: Recently, we found that rRNA synthesis in dissociated embryonic cells of Xenopus laevis is selectively inhibited by ammonium salts added to their surrounding medium. Similar effects were also observed in cells treated with amines. In this report, we analysed in more detail the effects of an ammonium salt and trimethylamine on rRNA synthesis in Xenopus embryonic cells cultured under several different conditions. Results obtained showed that ammonia and trimethylamine inhibit formation of 40S pre-rRNA, without inducing breakdown (wastage) or aberrant processing of the 40S pre-rRNA. Such inhibitory effects were also shown not to be due to interference with cellular ATP level. Furthermore, we found that the effects of both ammonium salt and trimethylamine were completely abolished when Na+ in the culture medium of the testing cells was replaced by choline ions. These results favour the view that the inhibition of rRNA synthesis by ammonia and amine is realized at the transcriptional level or at the step before the formation of 40S pre-rRNA, most probably via a slight increase of intracellular pH, but not via an inhibition in energy-generating systems.
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008744:Methylamines / Q000494:pharmacology*; D012322:RNA Precursors / Q000096:biosynthesis; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D014981:Xenopus
chemical_list: D008744:Methylamines; D012322:RNA Precursors; D012335:RNA, Ribosomal; D000643:Ammonium Chloride; C023336:trimethylamine