Stimulatory, permeabilizing, and toxic effects of amphotericin B on L cells

High concentrations of amphotericin B (AmB) killed mouse L cells, but low concentrations increased plating efficiency and stimulated the incorporation of labeled precursors into DNA and RNA. Thus, there were two disparate effects of AmB on L cells, stimulatory and toxic, and they occurred in distinct dose-related stages. AmB also affected the permeability of L cells. In dose-response studies, increases in cell membrane permeability, measured as the loss of K+ ions, occurred along with the stimulation of [3H]uridine incorporation into RNA. In contrast, stimulation of [3H]thymidine incorporation into DNA was only observed in cells recuperating from AmB-induced permeability changes. When the K+ concentration in the medium was lowered to 0.5 from 4.5 mM, or when 1 mM ouabain was added to the cultures, cell killing was potentiated, but the stimulatory and permeabilizing effects of subtoxic concentrations of AmB were unaffected. Furthermore, etruscomycin, a polyene antibiotic without any permeabilizing effects, nevertheless induced an enhancement of plating efficiency and of incorporation of [3H]uridine into RNA and [3H]thymidine into DNA. Our results suggest that the dose-related stimulatory, permeabilizing, and toxic effects of AmB most probably have distinct mechanisms of action and may be independent of one another.