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Brief periods of ischemia and reperfusion that precede sustained ischemia lead to a reduction in myocardial infarct size. This phenomenon, known as ischemic preconditioning, is mediated by signaling pathway(s) that are yet to be fully defined. 3'-Phosphoinositide-dependent kinase-1 (PDK1) has been implicated in numerous cellular processes. However, the involvement of PDK1 in preconditioning has yet to be elucidated. Studying PDK1 is not as straightforward as it is for the majority of kinases, due to the lack of a specific inhibitor of PDK1. Therefore, we have taken advantage of PDK1 hypomorphic mutant mice with reduced expression of PDK1 to study the role of PDK1 in preconditioning. Whole heart and single cell models of preconditioning demonstrated that the hearts and cardiac cells from PDK1 hypomorphic mice could not be preconditioned. The cardioprotective effect of PDK1 was not related to the effect that preconditioning has on sarcolemmal membrane action potential as revealed by di-8-ANEPPS, a sarcolemmal-potential sensitive dye, and laser confocal microscopy. In contrast, experiments with JC-1, a mitochondrial membrane potential-sensitive dye, has demonstrated that intact PDK1 levels were required for preconditioning-mediated regulation of mitochondrial membrane potential. Western blotting combined with functional experiments have shown that intact PDK1 levels were required for preconditioning-induced phosphorylation of protein kinase B (PKB), glycogen synthase kinase-3beta (GSK-3beta), and cardioprotection. We conclude that PDK1 mediates preconditioning in the heart by regulating activating PKB-GSK-3beta to regulate mitochondrial but not sarcolemmal membrane potential. 3'Phosphoinositide-dependent kinase-1 (PDK1) is essential for ischemic preconditioning of the myocardium.

The influence of benzene on 3 and 24 months old rat liver microsomes was studied. Some structural and functional changes occur under benzene treatment in the cytochrome P-450 system which are more pronounced in 3 months old rat microsomes than in the 24 months ones. Glucose-6-phosphatase and glucose dehydrogenase activities indicate that 3 months old rat microsomal vesicles are more stable against benzene injury than those, of 24 months old ones. In vitro benzene hydroxylation activation by NADPH addition decreased disruptive xenobiotic's effect on 3 but not on 24 months old rat liver microsomal vesicles. This fact suggests that the rate of benzene hydroxylation is important for its membrane damaging action effect. Thus, age-related differences in xenobiotic action on liver microsomes could be related to the decrease of benzene metabolism rate with senescence.

In the present study the increase of glucose concentration in the blood serum of 24-month old rats after 2-days benzene treatment has been shown. Benzene action caused a decrease in the activity of microsomal glucose-6 phosphatase and increase in that of microsomal glucose dehydrogenase in the liver of 3-month old (but not 24-month old) rats. It is supposed that the mechanism of benzene hyperglycemia action is based on the fall in the intensity of glucose utilization by peripheral tissues, and the decrease in hepatocytes adaptation possibilities with senescence is the cause for the studied age differences.

The influence of EDTA on the CO-differential spectra of cytochrome P-420 formed in the rat liver microsomes under the effect of 1 mM CuCl2 in the presence of dithionite has been studied. It was shown that the level of revealed cytochrome P-420 was diminished two-fold following 10 mM EDTA addition if dithionite concentration initially added to the medium was about 2 mM. Cytochrome b5 had no changes. Cytochrome P-420, formed under the effect of desoxycholate, was insensitive to EDTA, but its amount decreased after addition of CuCl2. It is supposed to proceed under chelatation of heme Fe(II).