ARSENITE INDUCED SENSITIZATION AND SELF-TOLERANCE OF REUBER H35 HEPATOMA-CELLS

Our data show that a short incubation with arsenite (30-300 muM) induc es a biphasic change in cellular sensitivity towards a second exposure to arsenite. A transient sensitization was followed by the developmen t of self-tolerance. Sensitization was measured using the step-down pr otocol; i.e., application of a high dose of arsenite pretreatment (100 or 300 muM) followed immediately by incubation in a low dose of arsen ite (1-30 muM), with extensive rinsing in between. Whereas no effect o f 1 and 3 muM on cellular survival is observed without pretreatment, a large decrease in cell survival can be established when these low dos es of arsenite are applied immediately after a 1 hr pretreatment with 100 or 300 muM arsenite. According to the step-down protocol, a high d ose of toxic compounds is applied and is followed by prolonged incubat ion in a lower concentration of the initial toxic compound. This might be a more accurate model for studying the effects of toxic insults on cells and organisms in the manner in which they occur in their natura l environment. The level of tolerance was determined by a 1 hr test tr eatment with 300 muM arsenite applied at different times after pretrea tment. Using this fractionated treatment protocol, it was established that tolerance increases with the increasing time intervals between th e sodium arsenite treatments, during the 6 hr studied. These observati ons suggest that sensitization gradually decreases, whereas tolerance develops. Furthermore, our data indicate that the condition of pretrea tment determines the extent to which the early sensitivity increases, as well as the development of tolerance later on. A relatively high ar senite concentration leads to more sensitized cells, which are transfo rmed into more tolerant cells in comparison with the effect of a lower arsenite concentration.