Potential role of connexin43 in carbenoxolone‐promoted opening of the permeability transition pore in isolated brain and heart mitochondria

Abstract

Carbenoxolone (Cbx) was reported to induce permeability transition pore (PTP) opening in isolated rat liver mitochondria (RLM), although the mitochondrial molecular target of Cbx has yet to be identified. Here, we investigated the effects of Cbx on Ca2+‐induced PTP opening in RLM, rat heart (RHM), and rat brain (RBM) mitochondria. In RLM, RHM, and RBM, threshold Ca2+ load induced PTP opening, as seen by sudden Ca2+efflux from the mitochondrial matrix and a drop in membrane potential. At about 1 μM, Cbx enhanced Ca2+‐induced CyclosporinA‐sensitive PTP opening. Since in isolated heart mitochondria Connexin43 (Cx43) was found, we suggested that Cbx might be target for Cx43 in mitochondria. We detected Cx43 by Western blot in the outer RBM membrane and in mitoplasts, but not in RLM. Anti‐Cx43 antibody abolished Cbx‐enhanced PTP opening in RBM but not in RLM, supposing possible involvement of another connexin type in RLM. Besides being a gap junction inhibitor, Cbx bears structural similarity to corticosteroids, indicating possible translocator protein (TSPO)/ peripheral‐type benzodiazepine receptor (PBR) targeting. Cbx‐enhanced PTP opening, which correlated with increased protein phosphorylation, was suppressed by an anti‐TSPO antibody. All these results indicate that Cbx facilitates Ca2+‐induced PTP opening having as possible targets in RHM and RBM both TSPO and Cx43.