Long-term impact of sublethal atrazine perturbs the redox homeostasis in pea (Pisum sativum L.) plants

Atrazine frequently contaminates soil, groundwater, rivers, and ponds. It is well know that acute doses (1–5 mM) of atrazine induce massive generation of singlet oxygen by blocking photosystem II. The sublethal concentrations of this herbicide, similar to those found in the environment, also reduce growth and disrupt photosynthesis in a long-term aspect, but exact mechanisms remain much uncertain. In this study the effects of environmentally relevant atrazine levels, ranging from 0.1 to 10 μM, on pea plants were characterized for up to 20 days. The plants exposed to continuous influence of atrazine exhibited perturbed redox homeostasis with increases of the lipid peroxides, the total and oxidized glutathione pools and elevated guaiacol peroxidase and glutathione-S-transferase activities. In contrast, the long-term atrazine impact did not affect superoxide dismutase activity whereas the catalase was inhibited. The perturbations of the redox status and the recruitment of the antioxidant machinery imply that the sublethal atrazine concentrations alter the poise between production and scavenging of reactive oxygen species. Taken together these results show that the long-term impact of sublethal atrazine has hallmarks of oxidative stress most probably triggered by generation of singlet oxygen.     

STIM1 and STIM2 Proteins Differently Regulate Endogenous Store-operated Channels in HEK293 Cells

The endoplasmic reticulum calcium sensors stromal interaction molecules 1 and 2 (STIM1 and STIM2) are key modulators of store-operated calcium entry. Both these sensors play a major role in physiological functions in normal tissue and in pathology, but available data on native STIM2-regulated plasma membrane channels are scarce. Only a few studies have recorded STIM2-induced CRAC (calcium release-activated calcium) currents. On the other hand, many cell types display store-operated currents different from CRAC. The STIM1 protein regulates not only CRAC but also transient receptor potential canonical (TRPC) channels, but it has remained unclear whether STIM2 is capable of regulating store-operated non-CRAC channels. Here we present for the first time experimental evidence for the existence of endogenous non-CRAC STIM2-regulated channels. As shown in single-channel patch clamp experiments on HEK293 cells, selective activation of native STIM2 proteins or STIM2 overexpression results in store-operated activation of I_min channels, whereas STIM1 activation blocks this process. Changes in the ratio between active STIM2 and STIM1 proteins can switch the regulation of I_min channels between store-operated and store-independent modes. We have previously characterized electrophysiological properties of different Ca²⁺ influx channels coexisting in HEK293 cells. The results of this study show that STIM1 and STIM2 differ in the ability to activate these store-operated channels; I_min channels are regulated by STIM2, TRPC3-containing I_NS channels are induced by STIM1, and TRPC1-composed I_max channels are activated by both STIM1 and STIM2. These new data about cross-talk between STIM1 and STIM2 and their different roles in store-operated channel activation are indicative of an additional level in the regulation of store-operated calcium entry pathways.     

Mechanisms by which cAMP increases bile acid secretion in rat liver and canalicular membrane vesicles

Bile acid secretion induced by cAMP and taurocholate is associated with recruitment of several ATP binding cassette (ABC) transporters to the canalicular membrane. Taurocholate-mediated bile acid secretion and recruitment of ABC transporters are phosphatidylinositol 3-kinase (PI3K) dependent and require an intact microtubular apparatus. We examined mechanisms involved in cAMP-mediated bile acid secretion. Bile acid secretion induced by perfusion of rat liver with dibutyryl cAMP was blocked by colchicine and wortmannin, a PI3K inhibitor. Canalicular membrane vesicles isolated from cAMP-treated rats manifested increased ATP-dependent transport of taurocholate and PI3K activity that were reduced by prior in vivo administration of colchicine or wortmannin. Addition of a PI3K lipid product, phosphoinositide 3,4-bisphosphate, but not its isomer, phosphoinositide 4,5-bisphosphate, restored ATP-dependent taurocholate in these vesicles. Addition of a decapeptide that activates PI3K to canalicular membrane vesicles increased ATP-dependent transport above baseline activity. In contrast to effects induced by taurocholate, cAMP-stimulated intracellular trafficking of the canalicular ABC transporters was unaffected by wortmannin, and recruitment of multidrug resistance protein 2, but not bile salt excretory protein (bsep), was partially decreased by colchicine. These studies indicate that trafficking of bsep and other canalicular ABC transporters to the canalicular membrane in response to cAMP is independent of PI3K activity. In addition, PI3K lipid products are required for activation of bsep in the canalicular membrane. These observations prompt revision of current concepts regarding the role of cAMP and PI3K in intracellular trafficking, regulation of canalicular bsep, and bile acid secretion.     

Properties of the enzymes of energy supply in the common frog under various physiological states. II. Changes in the heat resistance of adenosine triphosphatases and succinate dehydrogenase

The heat resistance of SDG, Na, K-ATPase and Mg-ATPase of the grass frog was determined in January, March and May, the number of animals examined being 30-40 in either experiment. It was found that the average level of the heat resistance of the enzymes studied shows significant, often differently directed changes, which depend on the physiological state of an organism. Negligible correlation between the thermal sensitivity of different enzymes of an organism during hibernation, completely disappear during the activity state.     

Store-operated calcium entry into SK-N-SH human neuroblastoma cells modeling huntington’s disease

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by expansion of polyglutamine at the N-terminus of the huntingtin protein. Striatal medium spiny neurons (MSN) are the primary targets of HD pathology. In our study, a cellular model of HD was based on the human neuroblastoma cells SK-N-SH transfected with plasmid for expression of the mutant huntingtin protein Htt138Q. Expression of Htt138Q increased store-dependent calcium entry into SK-N-SH cells. EVP4593 reversibly blocked the abnormal store-dependent response, probably generated by the channels incorporating TRPC1 ( transient receptor potential canonical 1) subunit.     

Time of the action of genes controlling the activity of aldolase in embryonal development of groudling]

The time of action of the genes controlling the decrease of aldolase activity (21-23 hrs of development) and its subsequent increase (23-36 hrs) was determined by means of inactivation of the nuclei by actinomycin or heavy doses of irradiation at succesive developmental stages. There exist two distinct periods of gene activity; the former (15-18 hrs) determines the rapid fall of maternal aldolase activity and the latter (21-27 hrs) its subsequent replacement by embryonic aldolase. This result is confirmed by the data concerning the changes in aldolase heat resistance in the hybrids of the loach and tropical cyprinids. The genes controlling the synthesis of the new aldolase and the morphogenesis which takes place at the same developmental stages are functioning at different times, i.e. the biochemical and morphological differentiations may occur relatively independently.