Mitochondrial permeability transition pore (MPTP) opening. MPTP opening was detected by using MitoProbe Transition Pore Assay Kit as described in the materials and methods. Mouse glomerular endothelial cell (MGECs) were treated with GYY4137 (GYY) (250 μM) and glucose (5 and 25 mM). A: black histogram represents fluorescent dye, calcein, in the cytosol and mitochondria; red histogram represents calcein in mitochondria only and quenching of cytosolic calcein by addition of CoCl2; blue histogram represents calcein fluorescence in cells treated with calcein-AM, CoCl2, and ionomycin, which stimulates the opening of MPTP. B: MGECs without GYY treatment showed reduced calcein fluorescence under high-glucose (HG) conditions in the presence of calcein-AM, CoCl2, and ionomycin (shifted blue histogram to the left). MGECs treated with GYY in HG conditions inhibited MPTP opening and increased calcein fluorescence (shifted blue histogram to the right). Representative images from n = 6 independent experiments. NG, normal glucose.