B. O. Manko, V. V. Manko

Ivan Franko National University of Lviv, Ukraine;
e-mail: mankobo@gmail.com

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 (K_0.5) 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 V_max 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 V_max. 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.

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