Tag Archives: digitonin
Different sensitivity of Na(+),K(+)-ATPase and Mg(2+)-АТРase to ethanol and arachidonic acid in rat colon smooth muscle under pretreatment of cellular membranes with Ds-Na
A. A. Kaplia
Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
e-mail: kaplya@biochem.kiev.ua
The methodological procedure provides the detection of the relatively high Na+,K+-ATPase functional activity in the crude cellular membranes of rat colon smooth muscle (CSM) following standard detergent pretreatment (with Ds-Na vs digitonin). It includes the essential discrete steps: detergent membrane permeabilization under optimal detergent/protein ratio and active site protection by ATP (for Ds-Na) prior enzymatic reaction with substantial detergent dilution far below critical micelle concentration in the ATPase medium. The high level of the Na+,K+-ATPase activity, originally detected in CSM, did not differ for two detergents and was comparable with ouabain-resistant Mg2+,АТР-hydrolase activity, The features of ATPase protein-lipid complexes were evaluated by the enzyme sensitivity to the effect of ethanol and arachidonic acid with different membrane disordering effectiveness. The long-chain fatty acid is a more effective inhibitor as compared with aliphatic alcohol for both ATPases. Mg2+,АТР-hydrolase appeared to be much more resistant to inactivation than Na+,K+-ATPase. The data reflect the possible differences in lipid dependence of two enzymatic systems due to the peculiarities of the structural arrangement in membrane and importance of the hydrophobic microenvironment for mechanism of catalysis. Thus, the data represent the approach to the simple and reliable Na+,K+-АТРase activity determination in nonpurified CSM membranes, acceptable for different tissues and appropriate for quantitative comparison in pathophysiological studies and for testing the impact of diverse effectors on Na+,K+-АТРase.
Experimental substantiation of permeabilized hepatocytes model for investigation of mitochondria in situ respiration
V. M. Merlavsky, B. O. Manko, O. V. Ikkert, V. V. Manko
Ivan Franko National University of Lviv, Ukraine;
e-mail: vvmanko@lnu.edu.ua
TTo verify experimentally the model of permeabilized hepatocytes, the degree of cell permeability was assessed using trypan blue and polarographycally determined cell respiration rate upon succinate (0.35 mM) and α-ketoglutarate (1 mM) oxidation. Oxidative phosphorylation was stimulated by ADP (750 μM). Hepatocyte permeabilization depends on digitonin concentraion in medium and on the number of cells in suspension. Thus, the permeabilization of 0.9-1.7 million cells/ml was completed by 25 μg/ml of digitonin, permeabilization of 2.0-3.0 million cells/ml – by 50 μg/ml of digitonin and permeabilization of 4.0-5.6 million cells/ml – by 100 μg/ml. Thus, the higher is the suspension density, the higher digitonin concentration is required. Treatment of hepatocytes with digitonin resulted in a decrease of endogenous respiration rate to a minimum upon 20-22 μg of digitonin per 1 million cells. Supplementation of permeabilized hepatocytes with α-ketoglutarate maintained stable respiration rate on the level higher than endogenous respiration at the corresponding digitonin concentration, unlike the intact cells. Respiration rate of permeabilized hepatocytes at the simultaneous addition of α-ketoglutarate and ADP increased to the level of intact cell respiration, irrespective of digitonin concentration. Addition of solely succinate and especially succinate plus ADP markedly intensified the respiration of permeabilized hepatocytes to the level higher than that of intact cells. The dependence of succinate-stimulated respiration on digitonin concentration reached maximum at 20-22 μg of digitonin per 1 million cells. Optimal ratio of digitonin amount and the cell number in suspension is expected to be different in various tissues.