NMDA impairs mitochondrial bioenergetic function. (a) Representative images depicting the MMP in MIN6 cells treated with NMDA (5 mM) for 48 hours. Cells were stained for JC-1 to measure the change in MMP and observed under the confocal microscope [Bar = 58 μm; *P < 0.05 vs the control (red); ^#P < 0.05 vs the control (green)]. Bar graphs showing (b) intracellular ATP content and (c) intracellular ATP/ADP ratio of MIN6 β-cells stimulated with 16.7 mM glucose for 30 minutes after preincubation with different concentration of NMDA (1, 5, and 10 mM) for 48 hours (n = 4; *P < 0.05 vs the 0 mM NMDA group; **P < 0.01 vs the 0 mM NMDA group). Bar graphs showing (d) intracellular ATP content and (e) intracellular ATP/ADP ratio of MIN6 β-cells stimulated with 16.7 mM glucose for 30 minutes after preincubation with NMDA (5 mM) alone or in combination with NAC (0.5 mM) for 48 hours [n = 4; (d) F = 20.907; (e) F = 7.300; *P < 0.05 vs the control group; ^#P < 0.05 vs the NMDA group]. (f) Western blot showing expression of OXPHOS complex proteins in control MIN6 cells, and cells treated with NMDA for 48 hours. Bar graphs quantifying OXPHOS protein expression in MIN6 cells exposed to NMDA (1 and 5 mM) for 48 hours (n = 4; *P < 0.05 vs the control group).