Confluent cultures of bovine aortic endothelial cells in 6-well plates were exposed to cadmium chloride (1, 3, or 5 μM) under the condition of simultaneous treatment or pretreatment with manganese (5 or 10 μM). Following a 24-hr incubation, the conditioning medium was removed, cells were washed twice with ice-cold CMF-PBS, lysed in 100 μL of sodium dodecyl sulfate sample buffer (50 mM Tris-HCl buffer solution containing 2% sodium dodecyl sulfate and 10% glycerol, pH 6.8), and incubated at 95°C for 5 min. To degrade proteins, aliquots (50 μL) of the resulting lysate were treated with nitric acid at 130°C for 2 days. The resulting preparation was then dissolved in 5 mL of 0.1 M nitric acid and used for determinations of intracellular cadmium (m/z = 114) or manganese (m/z = 55) using inductively coupled plasma mass spectrometry (Nexion 300S; PerkinElmer, Waltham, MA, USA). Further aliquots of the lysates (30 μL) were analyzed for DNA content using a fluorometric method (Kissane and Robins, 1958) according to the expression of cadmium or manganese (pmol/μg DNA).