The mechanism of mitochondrial membrane potential retention following release of cytochrome c in apoptotic GT1-7 neural cells

The relationship is investigated between mitochondrial membrane potential ( Delta Psi (M)), respiration and cytochrome c (cyt c) release in single neur al bcl-2 transfected cells ( GT1-7bcl-2) or GT1-7puro cells during apoptosi s induced by staurosporine (STS). Bcl-2 inhibited the mitochondrial release of cyt c and apoptosis. Three different cell responses to STS were identif ied in GT1-7puro cells: (i) neither Delta Psi (M) nor cyt c were significan tly affected; (ii) a decrease in Delta Psi (M) was accompanied by a complet e release of cyt c; or (iii) cyt c release occurred independently of a loss of Delta Psi (M). The endogenous inner membrane proton leak of the in situ mitochondria, monitored by respiration in the presence of oligomycin, was increased by STS by 92% in puro cells, but by only 23% in bcl-2 cells. STS decreased respiratory capacity, in the presence of protonophore, by 31% in puro cells and by 20% in bcl-2 cells. In the absence of STS, oligomycin hyp erpolarized mitochondria within both puro and bcl-2-transfected cells, indi cating that the organelles were net generators of ATP. However after 15 h e xposure to STS oligomycin rapidly collapsed residual mitochondrial polariza tion in the puro cells, indicating that Delta Psi (M) had been maintained b y ATP synthase reversal. bcl-2 cells in contrast, maintained Delta Psi (M) until protonophore was added. These results indicate that the maintenance o f Delta Psi (M) following release of cyt c may be a consequence of ATP synt hase reversal and cytoplasmic ATP hydrolysis in STS-treated GT1-7 cells.