Objective: 

The present study was purported to compare mitochondrial respiratory rates (RR) in liver and heart mitochondria isolated from aged (18–20 months) vs. adult (4–6 months) Sprague-Dawley rats (n=8/group).

Methods: 

Mitochondria were isolated by differential centrifugation and oxygen consumption was measured at 370C by classic and high-resolution respirometry, respectively. The Substrate-Uncoupler-Inhibitor Titration protocol was used as follows: complex I and complex II-dependent respiration was stimulated by glutamate + malate and succinate+rotenone, respectively (LEAK state) and subsequent ADP addition (OXPHOS state); cytochrome c addition evaluated mitochondria integrity; ATP synthase was inhibited by oligomycin; uncoupled respiration was obtained by FCCP titration in steps of 0.1 mM optimal concentration (ETS capacity); respiration was inhibited with antimycin A.

Results: 

RR (expressed in natomO2/min/mg) in aged vs. adult liver mitochondria for CI dependent respiration were: Leak 21.6±0.9 vs. 24.6±0.8 (p<0.05); Oxphos 100.7±2.1 vs. 124.8±5.6 (p<0.01); ETS 88.5±3.6 vs. 131.9±6.6 (p<0.001). A more important decrease of Leak state was obtained for CII supported respiration (33.5±0.8 vs. 42.6±0.8, p<0.001) with comparable results for the other parameters. For heart mitochondria RR (expressed in pmol/s*ml) were: (i) for CI dependent respiration: Leak, 41.6±5 vs. 48.3±2; Oxphos 480.2±85.2 vs. 673.4±32.5, ETS 470.4±63.8 vs. 548±24 and RCR (the ratio between Oxphos and Leak states) 11.5±1.9 vs. 13.62±1.10 (p<0.01); (ii) for CII dependent respiration: Leak 138.1±16.7 vs. 159.03±9.6 Oxphos 536.7±101.8 vs. 630.6±25.53; ETS 588.08±100.7 vs. 667.7±28.6 (p<0.01).

Conclusions: 

Our results showed an important decline for all respiratory parameters in the senescent group vs. adult group, in both liver and heart mitochondria energized with complex I and II substrates. Research supported by PhD fellowship POSDRU/88/1.5/S/63117.