Effect of Calcium on the Energy Status of Rat Brain Synaptosomes under Acidosis

A. V. Levko^*, S. L. Aksentsev, S. V. Fedorovich, and S. V. Konev

Institute of Photobiology, Academy of Sciences of Belarus, ul. Skoriny 27, Minsk, 220072 Belarus; fax: (375-172) 68-5359; E-mail: fed@bas07.basnet.minsk.by

^* To whom correspondence should be addressed.

Received July 1, 1997; Revision received September 4, 1997

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Incubation of rat brain synaptosomes at pH 6.0 in Ca²⁺-containing medium is associated with a decrease in the ATP content and the rate of oxygen consumption. ATP/ADP ratio decreased from 6.6 ± 0.24 at pH 7.4 to 3.2 ± 0.17 at pH 6.0. The content of ⁸⁶Rb⁺ and [³H]tetraphenylphosphonium measured at pH 7.4 did not change after preincubation at pH 6.0, indicating the absence of lesion of synaptosomal plasma membranes and intrasynaptosomal mitochondria. Incubation with 1 mM EGTA in Ca²⁺-free medium as well as addition of 1 mM ouabain or 10 µM ruthenium red prevents the effect of acidosis. Similar results were obtained when 5 mM pyruvate was used as a mitochondrial substrate instead of glucose. It is suggested that acidosis-induced decrease in the ATP level is associated with the increase in Ca²⁺ concentration in the cytoplasm and its transport into mitochondria. Ouabain reverses this process due to activation of Na⁺/Ca²⁺ exchange.

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KEY WORDS: synaptosomes, acidosis, ATP, calcium, mitochondria

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