The cytosensor microphysiometer (a biosensing instrument for detecting cellular metabolism) was compared to the established tetrazolium salt assay as a chemosensitivity test. Two coumarin compounds, 7-hydroxycoumarin and esculetin, were examined to determine their effect on the cellular metabolism of A431 cells over a 24-h exposure period. In the tetrazolium salt assay, 7-hydroxycoumarin caused suppression of the succinate dehydrogenase activity at concentrations greater than 10 microg/ml. Esculetin exerted a more serious effect on succinate dehydrogenase, with decreases in activity observed at greater than 1 microg/ml. The observed effect was dose-dependent for both compounds examined. The metabolic activities of cells exposed to 100 microg/ml of drug were 90.37 +/- 2.8 and 71.62 +/- 2.96 (n = 3), of control values, for 7-hydroxycoumarin and esculetin, respectively. Using the cytosensor microphysiometer to assess metabolic activities, a similar pattern of inhibition was observed, with esculetin more detrimental to cellular metabolism than 7-hydroxycoumarin. The effect was dose- and time-dependent for both compounds. 7-Hydroxycoumarin (100 microg/ml) caused the cellular metabolic rate to drop to 44.21 +/- 5.34% (n = 4) of the control metabolic rate, while 100 microg/ml esculetin caused the metabolic rate to fall to 21.5 +/- 4.54% (n = 4) of the control rate. The cytosensor method proved to be superior to the tetrazolium salt assay for a number of reasons, which are discussed in this paper.
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