Mitochondria in heart ischaemia and aging

We have examined the effect of dietary polyunsaturated fatty acids (PUFAs) upon mitochondrial Ca²⁺ content and dehydrogenase activation in the rat heart. Diets were either a conventional low-fat chow (Ref) or were rich in n-3 PUFAs from fish oils (n-3) or n-6 PUFAs from animal fat (n-6). We found that the n-3 diet minimized the rise in mitochondrial Ca²⁺ seen in response to positive inotropic intervention with noradrenaline, and also minimized the activation of pyruvate dehydrogenase, which is Ca²⁺ dependent. As the work output of all three groups of hearts was the same, this observation may explain the previous finding of increased thermodynamic efficiency of the n-3 heart relative to the n-6 heart. When hearts were subjected to low-flow ischaemia (15 min), followed by 5 min of reperfusion, increases of mitochondrial Ca²⁺ were less in the n-3 group than in the n-6 group. In more prolonged ischaemia and reperfusion, n-3 feeding may confer protection against mitochondrial Ca²⁺ overload, opening of the permeability transition pore and cell death. Notably, the effects of n-3 feeding on mitochondrial functioning were most apparent in hearts from senescent rats (23 months). This is consistent with our finding that the decrease in mitochondrial membrane cardiolipin content, and increase in phosphatidylcholine, which occurred with aging in the Ref and n-6 groups, was totally prevented by n-3 feeding. Thus there are a number of reasons to regard an n-3-rich diet as being protective of the heart in aging mammals.