Аннотация:In the present work, it was shown that under conditions of lowamplitude
swelling (the tonicity of incubation medium is
120 mOsm) of heart mitochondria, oxidizing succinate and producing
ATP, enzymes of oxidative phosphorylation system operate as a
tightly-bounded supercomplex. Firstly, the double-inhibitor titration
technique showed that under low tonicity (120 mOsm) partial
suppression of ATP synthesis by carboxyatractyloside (CATR) leads
to proportional suppression of the electron transport system activity.
So during the titration by malonate (the inhibitor of succinate
oxidase) there is no excess pull of electron-transfer enzymes. Under
isotonic conditions (300 mOsm), when no supercomplexes are
formed, partial suppression of ATP synthesis by carboxyatractyloside
(CATR) leads to the formation of excess pull of active electrontransfer
enzymes; as a consequence, low concentrations of malonate
do not lead to the reduction of the respiration rate. Secondly, the
decrease of inner membrane potential of mitochondria due to
suppression of electron transport system by malonate is much
greater under hypertonic (600 mOsm) and isotonic (300 mOsm)
conditions than under hypotonic conditions (120 mOsm). The
suppression of the electron transport system of submitochondrial
particles by 85% doesn't reduce the potential on its membranes.
Thirdly, at the same conditions when the changes in mitochondrial
functioning are observed we investigated the ultrastructure of rat
heart mitochondria by means of electron microscopy and small angle
neutron scattering (SANS). Both of these methods revealed structural
reorganizations of cristae at decreasing media tonicity from 300 to
90–120 mOsm. Electron microscopy revealed that in the case of
isotonic media inner mitochondrial membrane forms dense packed
lamellae, in the case of low tonicity most of the lamellae are
reorganized into tubular structures. These tubular cristae were
observed to pack in hexagon-like structures. SANS showed that under
isotonic conditions scattering curves have an interference peak
Abstracts e25corresponding to the distance between the lamellae which centers
around 220 Å. At swelling of heart mitochondria (90 mOsm) the
ordering sharply decreases and the interference peak becomes
negligible. Hereby it was proved that under conditions of lowamplitude
swelling of heart mitochondria the enzymes of respiration
system and ATP-synthesis system function as supercomplex and these
functional changes are accompanied by the changes of inner
mitochondrial membrane ultrastructure.