Calcium‐induced permeability transition in rat brain mitochondria is promoted by carbenoxolone through targeting connexin43

Abstract

Carbenoxolone (Cbx), a substance from the medicinal licorice is used for anti‐inflammatory treatments. Cbx was already shown to induce opening of the permeability transition pore (PTP) in rat liver mitochondria (RLM). We investigated the mechanism of action of Cbx on Ca2+‐induced PTP opening in rat brain mitochondria (RBM), and in rat heart mitochondria (RHM) and in RLM, in an attempt to identify the molecular target of Cbx in mitochondria. In RBM, RHM and RLM, threshold Ca2+ load induced PTP opening. This was manifested by sudden Ca2+efflux from the mitochondrial matrix, a drop in membrane potential, and swelling of mitochondria. At 1 μM, Cbx enhanced the Ca2+‐induced, Cyclosporine A‐sensitive PTP opening. A well‐known target of Cbx in cells is the connexin family of proteins, which form gap junctions. Moreover, Connexin43 (Cx43) was previously found in RHM and attributed to the protective mechanism induced by ischemic preconditioning. We hypothesized that Cx43 might be a target for Cbx in brain mitochondria. We clearly detected Cx43 by Western blot in RBM and in mitochondria isolated from astrocytes, less in RHM, but not in RLM. Interestingly, the anti‐Cx43 antibody abolished the Cbx‐enhanced PTP opening in RBM, but not in RLM. In RBM, PTP caused serine‐368 phosphorylation of Cx43. These results show that Cbx facilitates Ca2+‐induced PTP opening, addressing as possible molecular target Cx43 in brain mitochondria.