Fig. 2.

An example trace of fish gill mitochondrial respiration and normalization to markers of mitochondrial volume. (A) Representative experiment at 12°C on permeabilized gill fibres to measure mitochondrial respiration rate during oxidative phosphorylation. L_N, LEAK respiration in the absence of ADP; P_PM, oxidative phosphorylation (OXPHOS) with pyruvate and malate; P_PMG, OXPHOS with pyruvate, malate and glutamate; P_PMGS, OXPHOS with pyruvate, malate, glutamate and succinate; L_Omy, LEAK respiration via oligomycin inhibition of ATP synthase; State 5, non-mitochondrial oxygen consumption; and P_TM; complex IV respiration with TMPD and ascorbate as electron donors. (B,C) Relationship between maximal respiration rate (P_PMGS) and either (B) citrate synthase (CS) activity or (C) cytochrome c oxidase (COX) activity, two common markers of mitochondrial abundance. Data points represent individual measurements and dashed lines represent linear regression lines. The slope for respiration rate versus CS activity was significantly different from zero (R²=0.689, n=8, P=0.011) while that for respiration rate versus COX activity was non-significant (R²=0.426, n=8, P=0.079).