Bax, a pro-apoptotic member of the Bcl-2 family of proteins has the ability to 
form transmembrane pores large enough to allow cytochrome c (Cyt c) release, as 
well as to activate the mitochondrial permeability transition pore (mPTP); 
however, no differential study has been conducted to clarify which one of these 
mechanisms predominates over the other in the same system. In the present study, 
we treated isolated mitochondria from MCF7 cells with recombinant protein Bax 
and tested the efficacy of the mPTP inhibitor cyclosporin A (CsA) and of the Bax 
channel blocker (Bcb) to inhibit cytochrome c release. We also, induced 
apoptosis in MCF7 cell cultures with TNF-α plus cycloheximide to determine the 
effect of such compounds in apoptosis induction via mPTP or Bax oligomerization. 
Cytochrome c release was totally prevented by CsA and partially by Bcb when 
apoptosis was induced with recombinant Bax in isolated mitochondria from MCF7 
cells. CsA increased the number of living cells in cell culture, as compared 
with the effect of Bax channel blocker. These results indicate that mPTP 
activation is the predominant pathway for Bax-induced cytochrome c release from 
MCF7 mitochondria and for apoptosis induction in the whole cell.