Induction of calcium-dependent nonspecific permeability of the inner membrane in liver mitochondria of mammals and birds: A comparative study

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The kinetics of the processes accompanying the induction of Ca²⁺-dependent permeability (pore opening) of the inner membrane—swelling of organelles and Ca²⁺ release from the matrix—was studied in isolated liver mitochondria of mammals (mice, rats, and rabbits) and birds (pigeons and guinea fowls). It was found that the mitochondria of rats, pigeons, and guinea fowls of the gray-speckled population (GSP) are similar in terms of respiration and oxidative ATP synthesis, whereas mitochondria of rabbits exhibit a greater degree of coupling of respiration and ATP synthesis, and mitochondria of mice and Zagorskaya White breed (ZWB) guinea fowls, a lower degree of coupling. It was established that mammalian mitochondria energized by succinate oxidation and incubated with 1 mM of inorganic phosphate are able to swell upon the addition of 125 nmol of CaCl₂ per 1 mg protein. Under these conditions, mitochondria of GSP and ZWB guinea fowls and pigeons are capable of swelling upon addition of at least 875, 875 and 1000 nmol of CaCl₂ per 1 mg protein, respectively. Cyclosporin A (CsA, 1 μM) inhibits mitochondrial swelling. It was shown that mitochondria of mammalians and guinea fowls but not of pigeons are able to effectively absorb and retain Ca²⁺ in the matrix. Calcium retention capacity of mitochondria from rats, mice, rabbits, GSP, and ZWB guinea fowls were, respectively, 70, 57, 38, 844 and 793 nmol of CaCl₂ per 1 mg of protein. In the presence of an oxidizing agent tert-butylhydroperoxide (TBH), the induction of the Ca²⁺-dependent pore in the mitochondria was observed upon addition of CaCl₂ in substantially smaller quantities. TBH was most effective in the case of rabbit mitochondria and had the lowest efficiency in the case of guinea fowl and pigeon mitochondria.