Insulin stimulates mitochondrial protein synthesis and respiration in isolated perfused rat heart

The rates of synthesis of mitochondrial proteins by both the cytoplasmic and mitochdrial protein synthetic systems, as well as parameters of respiration, were measured and compared in mitochondria isolated from fresh, control perfused, and insulin-perfused rat hearts. The respiratory control ratio (RCR) in mitochondria from fresh hearts was 8.1 ± 0.4 and decreased to 6.0 ± 0.2 (P < 0.001 vs. fresh) in mitochondria from control perfused hearts and to 6.7 ± 0.2 (P < 0.005 vs. fresh and P < 0.02 vs. control perfused) for mitochondria from hearts perfused in the presence of insulin. A positive correlation between the RCR and the rate of mitochondrial translation was demonstrated in mitochondria from fresh hearts. In mitochondria isolated from control perfused hearts, the rate of protein synthesis decreased to 84 ± 3% of the fresh rate after 30 min of perfusion and fell further to 64 ± 3% after 3 h of perfusion. The inclusion of insulin in the perfusion buffer stimulated mitochondrial protein synthesis 1.2-fold by 1 h (P < 0.005) and 1.34-fold by 3 h of perfusion (P < 0.001). The addition of insulin to 1-h control perfused hearts shifted the rate of mitochondrial protein synthesis from the control level to the insulin-perfused level within 30 min of additional perfusion, whereas 1 h was required to shift the RCR values of these mitochondria from control levels to insulin-perfused levels. Thus, whereas RCR was a useful predictor of mitochondrial translation rates, it did not account for the effects of insulin on mitochondrial translation. Insulin had no effect on the pattern of translation products labeled, suggesting that insulin stimulated the overall rate of mitochondrial translation. On cytoplasmic ribosomes, insulin stimulated the rate of synthesis of average total proteins and mitochondrial proteins identically, indicating an overall increase in the rate of cytoplasmic translation.