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 neural bcl-2 transfected cells (GT1-7bcl-2) or GT1-7puro cells during apoptosis induced by staurosporine (STS). Bcl-2 inhibited the mitochondrial release of cyt c and apoptosis. Three different cell responses to STS were identified in GT1-7puro cells: (i) neither Delta Psi(M) nor cyt c were significantly affected; (ii) a decrease in Delta Psi(M) was accompanied by a complete 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 hyperpolarized mitochondria within both puro and bcl-2-transfected cells, indicating that the organelles were net generators of ATP. However after 15 h exposure to STS oligomycin rapidly collapsed residual mitochondrial polarization in the puro cells, indicating that Delta Psi(M) had been maintained by ATP synthase reversal. bcl-2 cells in contrast, maintained Delta Psi(M) until protonophore was added. These results indicate that the maintenance of Delta Psi(M) following release of cyt c may be a consequence of ATP synthase reversal and cytoplasmic ATP hydrolysis in STS-treated GT1-7 cells.