Endogenous and exogenous regulators of activation of Ca-ATPase SERCA2

Alekseeva O.M.

N.M. Emanuel Institute of Biochemical Physics of Russian Academy of Sciences, Russia, 119334, Moscow, Kosygin St. 4, +74959397409,

One of the famous points of muscle contraction regulation at white skeletal muscle is the function of Ca2+-depot of sarcoplasmic reticulum (SR). Our work used samples of fragmented of reticulum (FSR), cleaned from mitochondria and its fragments. The samples of FSR were isolated from different regions with different functions- longitudinal tubules (FSRlt) and terminal cisternae (FSRtc). As the exogenous regulator the methylksantin caffeine was used. As endogenous regulator Mg2+ ions were used. It is known, that divalent ions Mg2+ and Са2+ play the great roles at regulation processes of enzyme activity.

The main task of our work was the investigation of endogenous and exogenous factors influence to the regulation of Ca-ATPase SERCA2 activity – the main Са2+-pump at SR. Mg2+-ATP was binding with high affinity at ATP-binding centre of Ca-ATPase, when the translocation of ions Са2 was activated. Translocation was conjugated with ATP hydrolysis. At the absence of Mg2+ the enzyme process was inhibited. Caffeine acts to the Са2+-channels and release of Са2+ions occurs. By this, the effectiveness of Са2+-pump decreased, because the ATP-hydrolysis are separated from Са2+-accumulation to the FSR lumen. At our work the data about the caffeine and Mg2+ influences to the Ca-ATPase SERCA2 activity at FSRtc and FSRlt was presented. FSRtc membranes contain the Са2+-pump and the Са2+-channels. FSRlt contain the Са2+-pump only. The model of caffeine-depended regulation of Са2+-accumulation to the FSR lumen, when the Ca-ATPase worked, was reinforced by changing of Mg2+ ions concentrations. Also for these the purposes the changing of passive permeability of FSR was made. The hydrophobic fractions of FSR membrane was enriched with free fatty acid (FFA), or FFA was extracted from membrane. Caffeine effect at FSRtc, cleaned from FFA, decreased in comparison with native FSRtc, under the Mg2+ concentrations changing 1mM to 4mM. FFA extraction decreased the caffeine effect to 15-20%. Under the enriching FSRtc membranes by FFA the maximal increasing of passive Са2+-permeability of hydrophobic membrane phase was obtained at Mg2+ 2 mM. The FSRlt samples had not the caffeine effect – the separations of Са2+-accumulation to the FSR lumen with ATP hydrolysis were not obtained. However, extraction or enriching of FSRlt by FFA influenced to the passive Са2+-permeability of hydrophobic membrane phase. And respectively these treatments influenced to the effectiveness of Са2+-accumulation to the FSR lumen.

The permeability of reticulum hydrophobic phase influences to the Са2+-gradient the through FSR membrane. These fact changes the relationships between the Са2+-pump and the Са2+-channels. Respectively, the variations of concentrations of endogenous and exogenous modulators Mg2+ ions, FFA or methylxanthines additions may be make it possible to influence on the processes of muscle functions at normal and pathology.

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