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A study was made of the effects of kaolinite, an aluminum silicate found in cigarette smoke and in alveolar macrophages of cigarette smokers, on the in vitro function of rabbit alveolar macrophages. Macrophages lavaged by standard procedures were incubated as adherent monolayers in the presence or absence of kaolinite, and amino acid incorporation into protein and transport subsequently measured. In the presence of dialyzed serum, kaolinite slightly inhibited incorporation into protein during the first 2 to 3 hr of incubation, after which incorporation ceased and a large percentage of newly synthesized protein was released (50% effect at approximately 0.5 mg/ml kaolinite). A dual-isotope experiment indicated that any change in the synthesis of protein which may have occurred was not selective for any protein or group of proteins. Kaolinite also stimulated noncompetitive amino acid accumulation after 2 to 3 hr in the presence of serum. The effects of kaolinite were immediate when incubations were conducted in the absence of serum. Control experiments showed all of the effects of the aluminum silicate to be on the cells and not on the incubation medium. These results suggest that kaolinite is cytotoxic and exerts its effects by a mechanism similar to that proposed for magnesium silicates and silica, in which the naked silicate is immediately cytotoxic, but if coated with serum protein must first be uncoated by lysozomal enzymes before destroying the cells.

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