Bioenergetic Response of Isolated Nerve Terminals of Rat Brain to Osmotic Swelling

A. V. Levko^*, A. A. Rakovich, and S. V. Konev

Institute of Photobiology, Belarus National Academy of Sciences, ul. Akademicheskaya 27, Minsk, 220072 Belarus; fax: (017) 268-5359; E-mail: kabash@biobel.bas-net.by

^* To whom correspondence should be addressed.

Received April 30, 1999; Revision received July 7, 1999

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The swelling of nerve terminals of rat brain in a hypotonic medium (230 mOsm) induced the potential-independent entrance of ⁴⁵Ca²⁺ into synaptosomes and intrasynaptosomal mitochondria that changed the energy status of synaptosomes, the rate of O₂ consumption and the content of ATP being decreased. The ratio ATP/ADP decreased from 6.5 ± 0.26 (310 mOsm medium) to 3.1 ± 0.18 (the medium 230 mOsm). Studies on the equilibrium distribution of K⁺ (⁸⁶Rb⁺) and [³H]TPP⁺ showed that contents of these cations in the nerve terminals were virtually the same on incubation in both iso- and hypotonic media. This indicated that the swelling did not damage intrasynaptosomal mitochondria and plasma membranes of the synaptosomes. The inhibition of oxidative phosphorylation increased twofold the rate of glycolysis. The incubation of synaptosomes in calcium-free medium (230 mOsm) in the presence of EGTA (1 mM) prevented the inhibition of oxidative phosphorylation and synthesis of ATP by the osmotic swelling. Ruthenium Red (10 µM) in the medium 230 mOsm inhibited the entrance of ⁴⁵Ca²⁺ into the intrasynaptosomal mitochondria and normalized the oxidative phosphorylation to the control level (310 mOsm medium). The decrease in the energy potential of synaptosomes induced by the hypoosmotic shock is suggested to be associated with the increase in Ca²⁺ content in the cytoplasm, its transport into the mitochondria, and the inhibitory effect on oxidative phosphorylation.

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KEY WORDS: synaptosomes, hypoosmotic swelling, ATP, calcium, mitochondria

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