Effects of cobalt on mouse neuroblastoma cells cultured in vitro.

To compare the effects of cobalt at different cellular levels, cultured mouse neuroblastoma cells (Neuro-2a) were exposed for 24 hr to cobalt(II) chloride. The following toxicity indicators were assessed: cell proliferation by quantification of total protein content; cytoplasmic membrane integrity to cytosolic lactate dehydrogenase leakage; lysosomal hexosaminidase release; lactate dehydrogenase activity (LDH); mitochondrial succinate dehydrogenase activity (SDH); relative neutral red uptake by lysosomes (RNRU); lysosomal hexosaminidase activity (HEX), and acetylcholinesterase activity (AChE). The effect of cobalt on the various indicators differed. Cobalt was not very toxic to neuroblastoma cell proliferation (EC(50) = 200 mum). Cytoplasmic membrane permeability was not specifically increased, and LDH leakage occurred only at high concentrations, prior to the stimulation of HEX activity, an enzyme involved in sphingolipid degradation. In contrast, cobalt was lysosomotropic, with HEX release. The effects on lysosomal function were also studied with the RNRU, showing stimulation at low concentrations and inhibition at high concentrations. Neural AChE was decreased after an initial stimulation at low concentrations. LDH and SDH intracellular activities were both stimulated from low concentrations, mitochondrial SDH activity being the most sensitive marker studied. Metabolic stimulatory effects induced by cobalt were, therefore, more marked than changes in cytoplasmic and lysosomal membrane permeability.