Fig. 1. Metabolic and mitochondrial responses to CO in heart. (A) Basal VO₂ and VCO₂ in Wt mice before and after CO exposure (1 hour, 1250 ppm). Gray bars indicate steady-state O₂ uptake and white bars CO₂ production. Values are the mean + s.e., n= 4 mice (P<0.05 less than pre-exposure control and ^*P<0.05 higher than pre-exposure control by repeated measures ANOVA). (B) 2D-PAGE of mouse cardiac mitochondria. Heart mitochondrial preparations of equal yield (2.5% of original protein) from a control and a CO-exposed mouse were carried simultaneously through 2D separation. The five respiratory complexes (I to V) showed approximately 1.5- to 2.2-fold increases in protein content 24 hours after CO (densitometry not shown). (C) Respiration rates in cardiac mitochondria of controls or mice 24 hours after CO exposure. State-4–State-3 per mg protein were similar except for higher succinate use after CO (mean + s.e., n=4; ^*P<0.05). (D) Low-temperature difference spectra (77°K) of cardiac mitochondria showing CO–cytochrome-a₃ complex formation (CO-a₃) and selective cytochrome b-c₁ reduction (Cyt bc₁). (E) TEM of longitudinal sections of hearts of control (left) and 24 hours after CO exposure (center) in Wt mice. Biogenesis is seen after CO in interfibrillar mitochondria (8000x magnification). Enlargement (right panel) shows budding (arrowhead) and dividing (arrows) mitochondria characteristic of mitochondrial biogenesis (22,000x magnification). The increase in mitochondrial density was approximately 30% 24 hours after treatment with CO by point counting.