Relationship between platelet mitochondrial biochemistry and the first wave of aggregation. Activity of platelet respiratory chain enzymes and the first wave of aggregation with ADP (4 μmol/l) were measured in healthy volunteers (white dots) and in patients with sepsis (grey dots) (within 48 hours from admission to intensive care). Nicotinamide adenine dinucleotide dehydrogenase (NADH) (A), complex I (CI) (B), complex I + III (CI + III) (C), succinate dehydrogenase (SDH) (D), complex II + III (CII + III) (E), and complex IV (CIV) (F) activity is expressed relative to citrate synthase (CS) activity, a marker of mitochondrial density. Aggregation was expressed as a percentage, where optical density of unstimulated platelet-rich plasma represents 0% and that of platelet-poor plasma is 100%. Strength of association between (normally distributed) variables was assessed with linear regression analysis and expressed as R
2. CS activity (expressed as nmol/minute/mg proteins) was not associated with the first wave of aggregation with ADP (R
2 = 0.00; P = 0.703). Complex I, NADH–ubiquinone 1 reductase; complex I + III, NADH–cytochrome c reductase; complex II + III, succinate dehydrogenase–cytochrome c reductase; complex IV, cytochrome c oxidase.