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• Andrienko 2003 J Exp Biol  + (Regulation of mitochondrial respiration bo … Regulation of mitochondrial respiration both by endogenous and exogenous ADP in the cells in situ was studied in isolated and permeabilized cardiomyocytes, permeabilized cardiac fibers and `ghost' fibers (all with a diameter of 10–20 µm) at different (0–3 µmoll^-1) free Ca²⁺ concentrations in the medium. In all these preparations, the apparent Km of mitochondrial respiration for exogenous ADP at free Ca²⁺ concentrations of 0–0.1 µmoll^-1 was very high, in the range of 250–350 µmoll^-1, in contrast to isolated mitochondria ''in vitro'' (apparent Km for ADP is approximately 20 µmoll^-1). An increase in the free Ca²⁺ concentration (up to 3 µmoll^-1, which is within physiological range), resulted in a very significant decrease of the apparent Km value to 20–30 µmoll^-1, a decrease of Vmax of respiration in permeabilized intact fibers and a strong contraction of sarcomeres. In ghost cardiac fibers, from which myosin was extracted but mitochondria were intact, neither the high apparent Km for ADP (300–350 µmoll^-1) nor Vmax of respiration changed in the range of free Ca²⁺ concentration studied, and no sarcomere contraction was observed. The exogenous-ADP-trapping system (pyruvate kinase + phosphoenolpyruvate) inhibited endogenous-ADP-supported respiration in permeabilized cells by no more than 40%, and this inhibition was reversed by creatine due to activation of mitochondrial creatine kinase. These results are taken to show strong structural associations (functional complexes) among mitochondria, sarcomeres and sarcoplasmic reticulum. Inside these complexes, mitochondrial functional state is controlled by channeling of ADP, mostly via energy- and phosphoryl-transfer networks, and apparently depends on the state of sarcomere structures.ondrial functional state is controlled by channeling of ADP, mostly via energy- and phosphoryl-transfer networks, and apparently depends on the state of sarcomere structures.)

• Andrienko 2003 J Exp Biol  +