Response differentials for either survival or NBD-PE accumulation were not evident with the nonphospholipogenic compounds, including compound D which consists of the right hand side aniline portion of the 5HT[1.sub.b] antagonist compound A and which does not contain a cationic phenylpiperazine moiety.
Figure 5 shows an 8 hr time-course of mitochondrial polarization status (as indicated by JC-1 fluorescence measurement), NBD-PE accumulation and rat cell survival following NMTMB treatments at concentrations that bracketed the 24 h survival [IC.sub.50] (159 [micro]M) and approached the approximate NBD-PE [EC.sub.50] (half maximal effective concentration, -65 [micro]M).
Similarly, for other phospholipogenics employed, when using concentrations that bracketed both 24 h survival [IC.sub.50] (half maximal inhibitory concentration) values and approximated NBD-PE [EC.sub.50] (half maximal effective concentration) values, hyperpolarization occurred at the lower test concentrations and depolarization was evident only when the 24 h [IC.sub.50] values were exceeded (data not shown).
Since mitochondrial changes occurred prior to measurable phospholipidotic responses (elevated NBD-PE) in our experiments with NMTMB, we tested whether lysosomal membrane integrity was intact at early time points.
We report that, against a panel of phospholipogenic treatments, dog hepatocytes exhibited lower 24 h survival [IC.sub.50] (half maximal inhibitory concentration) values and generally exhibited a diminished capacity to accumulate NBD-PE, that is, dog hepatocytes appeared less able to process phospholipogenics and mount phospholipidotic protective responses across broad concentrations ranges.