KINETIC PARAMETERS OF RESPIRATION IN RAT PERMEABILIZED HEPATOCYTES UPON Са 2+ IN VARIOUS CONCENTRATIONS IN MEDIUM AND PROLONGED INFLUENCE OF TAURINE

The dependence of permeabilized rat hepatocytes respiration rate on oxidation sub? strates concentration at presence 0.1 and 1 μM Са 2+ in the medium and amino sulfonic acid ? taurine ? effect on this subordination was studied. Experimental animals were in? jected with taurine (40 mg/kg of weight) for 28 days and control rats were injected with equal volume of water. Liver cells were permeabilized with digitonin (20 μg per 1 million cells). Respiration rate was determined by polarographic method using Clark’s electrode, upon either succinate or pyruvate with malate oxidation. Hill equation parameters were calculated applying {v; v/[S] h } coordinates. The kinetic dependence of respiration upon succinate and pyruvate oxidation is well described by Hill equation in the mediums with studied concentration of Са 2+ in control and under taurine action. Hill coefficient h and semi activation constant K 0.5 for succinate, at rotenone presence, are not changed in cont? rol animals after increase of Са 2+ сoncentration from 0.1 to 1 μM. Maximal velocity V max was slightly increased under such conditions. Kinetic parameters of respiration upon suc? cinate oxidation and both Са 2+ concentration, are not changed significantly under pro? longed taurine injection. There is more essential difference between kinetic parameters of pyruvate-stimulated respiration at various Ca 2+ concentrations. Thus, in control, V max is 1.5 times lower, and K 0.5 ? 10.7 times major at 0.1 μM Са 2+ in comparison with 1 μM Са 2+ . Hill coefficient becomes less than 1 at both Са 2+ concentration. As a result of taurine injection, V max is 1.6 times less at low Са 2+ and K 0.5 is higher, but only 6 times. Hill coefficient of this process increases at 0.1 μM Са 2+ and is 1.12, upon taurine impact. Substrate inhibition, inherent to the dependence of respiration rate on pyruvate concentration within the me? dium with 1 μM Са 2+ , starts developing, under taurine effect, at higher concentration of this substrate in comparison with control (3 mM comparatively to 0.35 mM). Thus, Са 2+ con? centration rise from 0.1 to 1 μM stimulates the rat hepatocytes mitochondria respiration upon exogenous pyruvate oxidation, but not succinate. Taurine under the prolonged in vivo action does not influence succinate-stimulated rotenone-insensitive respiration and intensifies processes of pyruvate-stimulated oxygen consumption in hepatocytes.