cell respiration of rat cardiomyocytes and soleus muscle fibers under ultra-short-term antiorthostatic suspension

The aim of the study was to analyses rat soleus fibers and left ventricle (LV) cardiomyocyte cell respiration after 6, 12, 18, 24 and 72 hours of antiorthostatic suspension by the tail. We measured V0 – basal oxygen consumption rate, V Glu+Mal – respiration velocity over a catalyst of malate and glutamate (5 mM glutamate + 2 mM malate) and Vmax – maximal respiratory rate (in the presence of 1 mM ADP) using the Saks polarography technique. We also determined the cytochrome c content and expression of its gene (Cycs) and the GAPDH gene using Western blotting and real-time PCR. Cell respiration parameters in cardiomyocytes increased after 18 hours of suspension: V0 increased by 35%, VGlu+Mal by 90% and Vmax by 85% in comparison with the control group (p<0.05). Cytochrome c content in a mix of the membrane and mitochondrial fractions grew by 34.6% (p<0.05) compared to control after 18 hours. However, Cycs and Gapdh expression rates remained stable. Protein content increase in this case may result from increased translation efficiency and/or a reduction in the level of proteolysis. Intensity of soleus fiber cell respiration decreased after 72 hours of suspension, V0 decreased by 76%, VGlu+Mal by 59% and Vmax by 53% compared to controls (p<0.05). Cytochrome c content fell after 24 hours of suspension by 15.7% (p<0.05) and by 57.9% (p<0.05) after 72 hours relative to controls. At the same time, Cycs mRNA content decreased after 6 hours of unloading by 23% (p<0.05) and continued to decrease to 59% (p<0.05) of the control level after 72 hours.