THAPSIGARGIN-INDUCED ENDOPLASMIC RETICULUM STRESS IS NOT ACCOMPANIED BY MITOCHONDRIAL MEMBRANE POTENTIAL DISSIPATION IN MURINE PRO-B CELLS

There are almost no data concerning the involvement of endoplasmic reticulum stress (Ca2+ fluxes) in the apoptosis of the pro-B cell type Ba/F3. Thus, we aimed the characterization of thapsigargin-induced effects on Ba/F3 cells in vitro. Material and method: For some experiments Ba/F3 cells were treated with 1 mu M thapsigargin for 24 hours. To compare, we used as positive control the effects of valinomycin 10 mu M. The negative control Ba/F3 cells received no treatment for 24 hours. After that, all batches of Ba/F3 cells were incubated in the presence of 1 mu M JC-1 (Sigma-Aldrich) at 37 degrees C for 30 minutes. Results: From the normal Ba/F3 JC-1-control cells (20.000 events gated by flow cytometry) 77.61 +/- 2.90% are associating high and 22.39 +/- 2.90% lower mitochondrial membrane potential. In the case of thapsigargin, 75.49 +/- 1.78% of the Ba/F3 cells are associating high and 24.51 +/- 1.78% lower mitochondrial membrane potential. Conclusions: While mitochondrial permeability transition pore (MPTP) opening necessarily correlates with a loss of mitochondrial membrane potential (psi(mt)), a decrease in psi(mt) does not necessarily indicate MPTP opening. Also, endoplasmic reticulum stress regulation of high cytosolic calcium levels by thapsigargin may prompt the opening of the MPTP without necessarily triggering irreversible pore activation or subsequent apoptogenic factors in Ba/F3 cells.