XTT reducing activity by CHO and L1210 cells was found to be stimulated by
the presence of cytochrome oxidase inhibitors such as NaN3 or KCN. Among th
e other respiratory chain inhibitors, antimycin A (a complex III inhibitor)
and chlorpromazine inhibited cellular XTT reduction, and rotenone and malo
nate showed slight inhibition and no effect,respectively. It is suggested t
hat XTT reduction is coupled with the respiratory chain via cytochrome, whi
ch is located between complexes III and IV (cytochrome oxidase).