Measurement of the matrix free Ca2+ concentration in heart mitochondria by entrapped fura-2 and quin2

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Abstract
A method was developed to monitor continuously the matrix free Ca2+ concentration ([Ca2+]m) of heart mitochondria by use of the fluorescent Ca2+ indicators, fura-2 and quin2. The acetoxymethyl esters of fura-2 and quin2 were accumulated in and hydrolysed by isolated mitochondria. An increase of the mitochondrial Ca content from 0.3 nmol/mg of protein to 6 nmol/mg corresponded to a rise of [Ca2+]m from 30 to 1000 nM. The results indicate that physiological fluctuations of the mitochondrial Ca content elicit changes of [Ca2+]m in that range which regulates the matrix dehydrogenases.