4HNE treatment decreases ATP synthesis but increases mitochondrial membrane potential. HL1 Cardiomyocytes were treated with 50 μM 4HNE for 24 hours and rescue was assessed with 10 μM carvedilol. (a, b) 4HNE adducts increased following 4HNE treatment. Carvedilol decreased 4HNE adducts(N=3/group). (c) 4HNE decreased cell count - the horizontal dotted line denotes the original number of plated cells (N=4–5/group). (d-i) Oxygen consumption was assessed in response to 4HNE using high resolution respirometry. (d) Summary of the oxygen consumption data. 4HNE decreased (e, f) leak respiration, (g) oxidative phosphorylation, (h) uncoupled respiration, and (i) respiratory control ratio (N=4/group). (j, k) However, 4HNE increased mitochondrial membrane potential, which further increased with carvedilol treatment (N=4–5/group). Carv - carvedilol; 4HNE - 4-hydroxynonenal; M+G - malate and glutamate; Succ - succinate; Oligo-oligomycin; FCCP - carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone; AM - antimycin; OxPhos - oxidative phosphorylation; RCR – respiratory control ratio; TMRM - tetramethylrhodamine, methyl ester; FSC – forward scatter; MFI – median fluorescence intensity. Data are presented as mean±SEM. **p<0.01.