Evaluating the role of dibutyl-cAMP and Ca++ as an MT inducer in a clonal rat hepatoma cell

Metallothioneins (MT) is a low molecular weight, cysteine-rich, metal-bindi ng protein that can be induced when cells and tissues are exposed to metal such as Cd, Zn, Cu and Hg. MT could also be induced by non-metallic stimuli including physiological, chemical and pathological stresses. It has been s uggested that signalling molecules such as cAMP or Ca++ might also induce M T. In the present study, the mode of induction of MT in the RH-35 cells was investigated with reference to the integrity of the cells. The degree of M T induction was measured by the Cd-saturation assay in which total Cd bound to the heat-stable MT was determined by the graphite furnace atomic absorp tion spectrometry. It was demonstrated that Zn and Cd could markedly increa se cellular MT content. Alpha-amanitin, which blocks DNA transcription, can significantly decrease the Cd induced MT induction. MT induction was also lowered by cycloheximide, which blocks protein translation. However, dibuty l-cAMP, Ca++ and Ca++ in the presence of ionomycin were unable to induce ce llular MT. Using this model, the results supported that notion that MT indu ction might not be mediated by cAMP or Ca++ in this cell line.