Age- and gender-related differences in mitochondrial oxygen consumption and calcium with cardioplegia and diazoxide

Abstract

Background: We have recently shown that the cardioprotection afforded by cardioplegia is affected by age and gender and is less effective in the aged female rabbit heart compared with the aged male rabbit heart. We hypothesized that these differences were due to age and gender-specific modulation of mitochondrial oxygen consumption and mitochondrial free matrix calcium ([Ca2+](Mito)) content occurring during early reperfusion.

Methods: To test this hypothesis, 104 male and female rabbit hearts, mature (15 to 20 weeks) and aged (>32 months), were subjected to Langendorff perfusion. Control hearts were perfused for 75 minutes. Global ischemia hearts were underwent 30 minutes of equilibrium, 30 minutes of global ischemia, and 15 minutes of reperfusion. Cardioplegia (potassium/magnesium) +/- diazoxide was infused 5 minutes before global ischemia. Mitochondria were isolated from left ventricular tissue and used for the measurement of oxygen consumption and [Ca2+](Mito).

Results: Mitochondrial oxygen consumption was significantly increased in the mature and aged female hearts in all treatment groups (p < 0.001 versus male). Cardioplegia +/- diazoxide modulated mitochondrial oxygen consumption, but these effects were significantly decreased in the aged heart and in the female heart (p < 0.001 each versus male). Cardioplegia (potassium/magnesium) significantly decreased [Ca2+](Mito) (p < 0.001 versus global ischemia) in aged but not mature hearts. The addition of diazoxide to potassium/magnesium significantly decreased [Ca2+](Mito) in mature and aged males (p < 0.001 versus potassium/magnesium) but not in females.

Conclusions: These results demonstrate that mitochondrial oxygen consumption and [Ca2+](Mito) are modulated by age and gender and play an important role in the differences observed between mature and aged male and female response to global ischemia and the cardioprotection afforded by cardioplegia +/- diazoxide.

Fig 1

Experimental protocol. Hearts were perfused for 30 minutes to establish equilibrium hemodynamics. Control hearts (top bar) were perfused without global ischemia at 37°C for 75 minutes. Global ischemia (GI) hearts (middle bar) underwent 30 minutes of perfusion for equilibrium (left clear area), 30 minutes of GI (black area), and 15 minutes of reperfusion (right clear area). Potassium/magnesium (K/Mg) hearts and K/Mg + diazoxide (DZX) hearts (bottom bar) underwent 30 minutes of perfusion for equilibrium (right clear area), then received either K/Mg or K/Mg + DZX (gray area) at the start of global ischemia (black area) and 15 minutes of reperfusion (right clear area).

Fig 2

Left ventricular peak developed pressure (LVPDP) during 30 minutes of equilibrium, 30 minutes of global ischemia, and 15 minutes of reperfusion for control (clear square, filled square), global ischemia (GI; open circle, male; filled circle, female), potassium/magnesium (K/Mg; clear diamond, male; solid diamond, female), and K/Mg + diazoxide (DZX; clear triangle, male; filled triangle, female) hearts in (A) mature male (n = 8) and mature female (n = 7) and (B): aged male (n = 7) and aged female (n = 7). All results are shown as the mean ± standard error of the mean. *Significant differences at p < 0.001 versus control.

Fig 3

State 3 (active) oxygen consumption (adenosine diphosphate-stimulated respiration) in (A) malate-induced (complex I) and (B) succinate induced (complex II) energized mitochondria (nM O₂/min/mg mitochondrial protein) in mature male (white bars), mature female (black bars) and aged male (dotted bars) and aged female (gray bars), control (after 75 minutes perfusion) global ischemia (GI), potassium/magnesium (K/Mg), and K/Mg + diazoxide (DZX) energized mitochondria after 30 minutes of global ischemia and 15 minutes of reperfusion. All results are shown as the mean ± standard error of the mean (7 to 8 animals for each group). *Significant differences at p < 0.001 versus male treatment group. **Significant differences at p < 0.001 versus mature treatment group.