Quinidine-induced decrease of intracellular esterase activity in a hepatoma cell line

Using image-analyzing equipment, we measured the effect of quinidine on the activity of naphthol AS-D chloroacetate esterase, alpha-naphthyl butyrate esterase, alpha-naphthyl acetate esterase, and acid phosphatase in individual cells of a human Hep G2 hepatoma cell line. The impact of the drug on the morphology of the cells was also observed. Depending on the concentration of quinidine applied, various changes occurred, the most extreme being cell death. However, at some drug concentrations that did not appear to affect visible cell structures, the activity of the esterases was decreased. This lessened enzyme activity did not seem to be related to the enzymes leaking from the cells, because the activity of acid phosphatase was unaffected. Inhibition of the esterase activity was related to the interval of exposure to quinidine in the perfusing medium and to the concentration of the drug. We consider the system described here to be a potential replacement for experiments with animals in the study of hepatotoxicity.