Cà2+ influence on respiration processes upon streptozotocin-induced diabetes mellitus
V. Merlavsky, O. Ikkert, V. Manko
Ivan Franko National University of Lviv
4, Hrushevsky St., Lviv 79005, Ukraine
The experiments were carried out using underbred rat males (180–220 g). The animals were separated into two groups – control group (injection of physiological solution, 1 ml) and experimental group (single injection of streptozotocin intraperitoneally, 50 mg/kg). The respiration rate of intact hepatocytes was registered upon endogenous substrates oxidation and dinitrophenol (0.1 mmol/l) addition. The respiration rate of permeabilized hepatocytes was registered upon the endogenous and exogenous substrates oxidation – a mixture of pyruvate, malate and glutamate (5 mmol/l of each) or succinate (5 mmol/l), and ADP (750 μmol/l) and dinitrophenol (0.1 mmol/l) addition. Kinetic parameters of succinate-stimulated respiration were investigated upon succinate (from 0.1 to 5 mmol/l) adding to suspension of permeabilized hepatocytes containing ADP and rotenone. Mitochondrial energetic processes intensification in the liver cells was established at early stages of streptozotocin-induced diabetes mellitus development. Thus, respiration rate of intact hepatocytes in diabetic rats is 40.8% higher, than in control. The intensification of oxygen consumption by permeabilized hepatocytes in control rats upon all Ñà2+ concentrations in the medium (0.01, 0.1, 1 and 10 μmol/l) was observed under conditions of pyruvate, malate and glutamate mixture addition (state S4). The greater intensification of respiration by that mixture in diabetic animals was observed at 10 μmol/l Ñà2+. The following ADP addition (state S3) increases respiration rate in control at 0.01 and 0.1 μmol/l Ñà2+ in the medium only. ADP-stimulated respiration rate in diabetic rats is maximal at 1 μmol/l Ñà2+. Similar dependence of substrate- and ADP-stimulated respiration rate on Ñà2+ concentration in the medium was observed also upon succinate oxidation. In addition, upon succinate oxidation the maximal mitochondrial functional ability (a response to the ADP and dinitrophenol application) in control animals was observed at 0.1 μmol/l Ñà2+ within the medium and in experimental rats at 1 μmol/l Ñà2+. Hill coefficient h and Vmax of succinate-stimulated mitochondrial respiration in diabetic animals were decreased upon low Ñà2+ concentration (0.1 μmol/l). These parameters remained similar to the control at 1 μmol/l Ñà2+ in the medium. That was caused, obviously, by lowering of mitochondrial sensitivity to Ñà2+ toxic concentrations. So, at the early stages of streptozotocin-induced diabetes mellitus development, the hepatocytes respiration was intensified thanks to, in particular, the increase of resistance to toxic Ñà2+ amounts within mitochondrial matrix.
Keywords: hepatocytes, cell respiration, Ñà2+, diabetes mellitus, streptozotocin