Journal archive > 2013 > N 4 July-August

^{2+}ON KINETIC PARAMETERS OF PANCREATIC ACINAR

*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 [Ca^{2+}] – 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 [Ca

^{2+}] 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 (

*K*

_{0.5}) did not significantly change in the studied range of [Ca

^{2+}] while at 10

^{-7}M Ca

^{2+}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

*V*

_{max}at pyruvate oxidation increased from 0.077 ± 0.002 to 0.119 ± 0.002 and 0.140 ± 0.002 nmol O

_{2}/(s·million cells) due to the increase of [Ca

^{2+}] from 10

^{-7}to 5?10

^{-7}or 10

^{-6}M, respectively. At oxidation of succinate or glutamate Ca

^{2+}did not significantly affect

*V*

_{max}. Thus, the increase of [Ca

^{2+}] 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, Ca^{2+}, pyruvate, succinate, malate, kinetics, Hill equation, Michaelis-Menten equation.

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© The Ukrainian Biochemical Journal