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Journal archive > 2013 > N 4 July-August

INFLUENCE OF Са2+ ON KINETIC PARAMETERS OF PANCREATIC ACINAR
MITOCHONDRIA IN SITU RESPIRATION

B. O. Manko, V. V. Manko

Ivan Franko National University of Lviv, Ukraine;
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The dependence of respiration rate of rat permeabilized acinar pancreacytes on oxidative substrates concentration was studied at various [Ca2+] – 10-8–10-6 M. Pancreacytes were permeabilized with 50 µg of digitonin per 1 million cells. Respiration rate was measured polarographically using the Clark electrode at oxidation of succinate or pyruvate either glutamate in the presence of malate. Parameters of Michaelis-Menten equation were calculated by the method of Cornish-Bowden or using Idi-Hofsti coordinates and parameters of Hill equation – using coordinates {v; v/[S]h}. In the studied range of [Ca2+] the kinetic dependence of respiration at pyruvate oxidation is described by the Michaelis-Menten equation, and at oxidation of succinate or glutamate – by Hill equation with h = 1.11–1.43 and 0.50–0.85, respectively. The apparent constant of respiration half-activation (K0.5) did not significantly change in the studied­ range of [Ca2+] while at 10-7 M Ca2+ it was 0.90 ± 0.06 mM for succinate, 0.096 ± 0.007 mM for pyruvate and 0.34 ± 0.03 mM for glutamate. Maximum respiration rate Vmax at pyruvate oxidation increased from 0.077 ± 0.002 to 0.119 ± 0.002 and 0.140 ± 0.002 nmol O2/(s·million cells) due to the increase of [Ca2+] from 10-7 to 5?10-7 or 10-6 M, respectively. At oxidation of succinate or glutamate Ca2+ did not significantly affect Vmax. Thus, the increase of [Ca2+] stimulates respiration of mitochondria in situ of acinar pancreacytes at oxidation of exogenous pyruvate (obviously due to pyruvate dehydrogenase activation), but not at succinate or glutamate oxidation.

Key words: acinar pancreacytes, mitochondria in situ, respiration, Ca2+, pyruvate, succinate, malate, kinetics, Hill equation, Michaelis-Menten equation.

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