Tag Archives: calcium homeostasis

Mathematical modeling of calcium homeostasis in smooth muscle cells while activity of plasma membrane calcium pump is modulated

S. O. Karakhim, V. F. Gorchev, P. F. Zhuk, S. O. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: laserlab@biochem.kiev.ua;  kinet@biochem.kiev.ua

A mathematical model of intracellular calcium homeostasis in smooth muscle cells has been investigated by computer modelling method. The results of calculations showed that for the plasma membrane calcium pump (PMCA) the limiting rate (VmPM) increasing or the Michaelis constant (KmPM) decreasing result in a lowering of the Ca2+ concentration in cytosol and sarcoplasmic reticulum (SR); the slight VmPM decreasing or KmPM increasing result in fluent cytosolic Ca2+ strengthening due to slow basal influx (SBI) since a massive release of Ca2+ from SR does not occur. The further VmPM decreasing or KmPM increasing stimulate the Ca2+-induced Ca2+ release from SR and the system passes into oscillation mode; when the certain low VmPM or high KmPM level is reached the oscillations of Ca2+ concentration in cytosol are stopped, there is only first oscillation after which a new level of cytosolic Ca2+ concentration is formed fluently: this level is higher than in the initial basal condition (IBC). Sensitivity of myocytes with the lowering­ of VmPM or increasing KmPM to agonist action is rising but sensitivity of myocytes with increasing VmPM or decreasing KmPM to agonist action is reducing. If the PMCA parameters (VmPM or KmPM) are changed then passive influx of Ca2+ in cytosol from extracellular space remains virtually invariable and it is equal to SBI value during the whole process. Initial rate of PMCA in a new equilibrium condition (NEC) is equal virtually to initial rate in IBC: it allows to calculate a new value VmPM or KmPM  from cytosolic Ca2+ concentration in NEC.

Electrochemical potential of the inner mitochondrial membrane and Ca(2+) homeostasis of myometrium cells

Yu. V. Danylovych, S. A. Karakhim, H. V. Danylovych, O. V. Kolomiets, S. O. Kosterin

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: danylovych@biochem.kiev.ua

We demonstrated using Ca2+-sensitive fluorescent probe, mitochondria binding dyes, and confocal laser scanning microscopy, that elimination of electrochemical potential of uterus myocytes’ inner mitochondrial membrane by a protonophore carbonyl cyanide m-chlorophenyl hуdrazone (10 μM), and by a respiratory chain complex IV inhibitor sodium azide (1 mM) is associated with substantial increase of Ca2+ concentration in myoplasm in the case of the protonophore effect only, but not in the case of the azide effect. In particular, with the use of nonyl acridine orange, a mitochondria-specific dye, and 9-aminoacridine, an agent that binds to membrane compartments in the presence of proton gradient, we showed that both the protonophore and the respiratory chain inhibitor cause the proton gradient on mitochondrial inner membrane to dissipate when introduced into incubation medium. We also proved with the help of 3,3′-dihexyloxacarbocyanine, a potential-sensitive carbocyanine-derived fluorescent probe, that the application of these substances results in dissipation of the membrane’s electrical potential. The elimination of mitochondrial electrochemical potential by carbonyl cyanide m-chlorophenyl hуdrazone causes substantial increase in fluorescence of Ca2+-sensitive Fluo-4 AM dye in myoplasm of smooth muscle cells. The results obtained were qualitatively confirmed with flow cytometry of mitochondria isolated through differential centrifugation and loaded with Fluo-4 AM. Particularly, Ca2+ matrix influx induced by addition of the exogenous cation is totally inhibited by carbonyl cyanide m-chlorophenyl hydrazone. Therefore, using two independent fluorometric methods, namely confocal laser scanning microscopy and flow cytometry, with Ca2+-sensitive Fluo-4 AM fluorescent probe, we proved on the models of freshly isolated myocytes and uterus smooth muscle mitochondria isolated by differential centrifugation sedimentation that the electrochemical gradient of inner membrane is an important component of mechanisms that regulate Ca2+ homeostasis in myometrium cells.