Libor Mrnka

Publications of Libor Mrnka

• Potential and drawbacks of EDDS-enhanced phytoextraction of copper from contaminated soils.

  Authors: Michael Komárek, Ales Vanek, Libor Mrnka, Radka Sudová, Jirina Száková, Václav Tejnecký, Vladislav Chrastný

  Environmental pollution (Barking, Essex : 1987). 07/2010; 158(7):2428-38.

  Incubation and pot experiments using poplar (Populus nigra L. cv. Wolterson) were performed in order to evaluate the questionable efficiency of EDDS-enhanced phytoextraction of Cu from contaminatedIncubation and pot experiments using poplar (Populus nigra L. cv. Wolterson) were performed in order to evaluate the questionable efficiency of EDDS-enhanced phytoextraction of Cu from contaminated soils. Despite the promising conditions of the experiment (low contamination of soils with a single metal with a high affinity for EDDS, metal tolerant poplar species capable of producing high biomass yields, root colonization by mycorrhizal fungi), the phytoextraction efficiency was not sufficient. The EDDS concentrations used in this study (3 and 6 mmol kg(-1)) enhanced the mobility (up to a 100-fold increase) and plant uptake of Cu (up to a 65-fold increase). However, despite EDDS degradation and the competition of Fe and Al for the chelant, Cu leaching cannot be omitted during the process. Due to the low efficiency, further research should be focused on other environment-friendly methods of soil remediation.

• Development and activity of Glomus intraradices as affected by co-existence with Glomus claroideum in one root system.

  Authors: Martina Janoušková, Pascale Seddas, Libor Mrnka, Diederik van Tuinen, Anna Dvořáčková, Marie Tollot, Vivienne Gianinazzi-Pearson, Miroslav Vosátka, Armelle Gollotte

  Mycorrhiza. 05/2009;

  The co-existence of two arbuscular mycorrhizal fungal (AMF) species, Glomus intraradices and Glomus claroideum, in the root systems of plants was investigated in a greenhouse experiment aimed atThe co-existence of two arbuscular mycorrhizal fungal (AMF) species, Glomus intraradices and Glomus claroideum, in the root systems of plants was investigated in a greenhouse experiment aimed at reconstructing interactions during an early stage of primary succession on a coal-mine spoil bank in Central Europe. Two plant species, Tripleurospermum inodorum and Calamagrostis epigejos, were inoculated either with one or both AMF species. Fungal development, determined by trypan blue and alkaline phosphatase staining as well as by PCR amplification of rRNA genes with species-specific primers, and the expression of five genes with different metabolic functions in the intraradical structures of G. intraradices were followed after 6 and 9 weeks of cultivation. The two AMF closely co-existed in the root systems of both plants possibly through similar colonisation rates and competitivity. Inoculation with the two fungi, however, did not bring any additional benefit to the host plants in comparison with single inoculation; moreover, plant growth depression observed after inoculation with G. claroideum persisted also in mixed inoculation. The expression of all the assayed G. intraradices genes was affected either by host plant or by co-inoculation with G. claroideum. The effects of both factors depended on the time of sampling, which underlines the importance of addressing this topic in time-course studies.

• Melatonin inhibits prostaglandin E2- and sodium nitroprusside-induced ion secretion in rat distal colon.

  Authors: Libor Mrnka, Miroslav Hock, Markéta Rybová, Jirí Pácha

  European journal of pharmacology. 03/2008; 581(1-2):164-70.

  Although the gastrointestinal tract is a rich source of melatonin and possesses numerous melatonin-binding sites, the role of melatonin in this tissue has not yet been fully elucidated. In this workAlthough the gastrointestinal tract is a rich source of melatonin and possesses numerous melatonin-binding sites, the role of melatonin in this tissue has not yet been fully elucidated. In this work we focused on the role of melatonin in the modulation of ion transport in rat distal colon. Whereas melatonin had no effect on colonic secretion or caused only infrequent and small changes in the short circuit current (Isc) due to its solvent ethanol, this mediator significantly modulated the secretion elicited by some secretagogues. Out of the five substances tested (prostaglandin E(2); 5-hydroxytryptamine; bethanechol; histamine; sodium nitroprusside) melatonin inhibited the effect of prostaglandin E(2) (PGE(2)) and sodium nitroprusside (SNP). Melatonin concentration-dependently decreased PGE(2)-evoked Isc and this inhibitory effect was more obvious from the mucosal side. The basal level of cAMP in colonic mucosa was not influenced by melatonin, but this drug prevented a PGE(2)-induced increase in the level of cAMP. The neurotoxin tetrodotoxin blocked the inhibitory effect of melatonin on SNP-induced Isc. Our data suggests that melatonin takes part in the modulation of colonic ion transport. The modulatory effect of melatonin on PGE(2)-induced Isc occurs directly at the level of the epithelium, whereas the effect on SNP-induced Isc is indirect and located in tetrodotoxin-sensitive enteric neurons.

• Insight into the circadian clock within rat colonic epithelial cells.

  Authors: Martin Sládek, Markéta Rybová, Zuzana Jindráková, Zdena Zemanová, Lenka Polidarová, Libor Mrnka, John O'Neill, Jirí Pácha, Alena Sumová

  Gastroenterology. 10/2007; 133(4):1240-9.

  BACKGROUND & AIMS: The gastrointestinal tract exhibits diurnal rhythms in many physiologic functions. These rhythms are driven by food intake but are also preserved during food deprivation,BACKGROUND & AIMS: The gastrointestinal tract exhibits diurnal rhythms in many physiologic functions. These rhythms are driven by food intake but are also preserved during food deprivation, suggesting the presence of endogenous circadian rhythmicity. The aim of the study was to provide insight into the circadian core clock mechanism within the rat colon. Moreover, the potency of a restricted feeding regime to shift the circadian clock in the colon was tested. The question of whether the colonic clock drives circadian expression in NHE3, an electroneutral Na(+)/H(+) exchanger, was also addressed. METHODS: Daily profiles in expression of clock genes Per1, Per2, Cry1, Bmal1, Clock, and Rev-erbalpha, and the NHE3 transporter were examined by reverse transcriptase-polymerase chain reaction and their mRNA levels, as well as PER1 and BMAL1 protein levels, were localized in the colonic epithelium by in situ hybridization and immunocytochemistry, respectively. RESULTS: Expression of Per1, Per2, Cry1, Bmal1, Clock, Rev-erbalpha, and NHE3, as well as PER1 and BMAL1 protein levels, exhibited circadian rhythmicity in the colon. The rhythms were in phase with those in the liver but phase-delayed relative to the master clock in the suprachiasmatic nucleus. Restricted feeding entrained the clock in the colon, because rhythms in clock genes as well as in NHE3 expression were phase-advanced similarly to the clock in the liver. CONCLUSIONS: The rat colon harbors a circadian clock. The colonic clock is likely to drive rhythmic NHE3 expression. Restricted feeding resets the colonic clock similarly to the clock in the liver.

• Heterogeneous expression of melatonin receptor MT1 mRNA in the rat intestine under control and fasting conditions.

  Authors: Matús Soták, Libor Mrnka, Jirí Pácha

  Journal of pineal research. 10/2006; 41(2):183-8.

  Melatonin is found in mammalian central nervous system and various peripheral tissues including gastrointestinal tract (GIT) where it participates in the regulation of intestinal motility, bloodMelatonin is found in mammalian central nervous system and various peripheral tissues including gastrointestinal tract (GIT) where it participates in the regulation of intestinal motility, blood flow, immunomodulation, ion transport, cell proliferation and scavenging of free radicals. Some of these effects are achieved via melatonin binding to specific receptors, MT1 and MT2. As no thorough study on the expression of these receptors in the GIT has yet been done, the aim of this study was to determine the MT1 mRNA expression in the rat intestine under both control and fasting conditions. Our results suggest that MT1 mRNA is present in epithelial as well as subepithelial layer, with higher expression in the latter in all intestinal segments studied. The highest signal of the MT1 transcript along the rostro-caudal intestinal axis was found both in epithelial and subepithelial layers of the duodenum. Nevertheless, duodenal MT1 mRNA expression did not reach the level found in pituitary gland. In a 12:12-hr light:dark cycle a MT1 receptor expression in the subepithelial layer of rat distal colon did not manifest a significant diurnal rhythm. Short-term fasting increased the expression of MT1 transcript in the subepithelial layer of both the small and large intestine. During long-term fasting the increase persisted only in distal colon while a return to control levels was observed in small intestinal segments. In conclusion we demonstrated heterogeneous expression of MT1 receptor in the rat intestine and showed that its expression is up-regulated by nutritional deprivation.

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• Age-dependent effect of secretagogues during colonic maturation.

  Authors: Libor Mrnka, Sergej Beskid, Oksana Sevastyanova, Jana Bryndová, Jirí Pácha

  European journal of pharmacology. 07/2005; 516(3):268-75.

  Intestinal secretory response is altered during colonic development. The aim of this report was to study the developmental changes of the Ca(2+)- and cAMP-induced regulatory pathways with specialIntestinal secretory response is altered during colonic development. The aim of this report was to study the developmental changes of the Ca(2+)- and cAMP-induced regulatory pathways with special attention to the direct and indirect effect of secretagogues on the colonic epithelium. We investigated the effect of bethanechol, 5-hydroxytryptamine (5-HT), and histamine on Cl(-) secretion and stimulation of intracellular Ca(2+) ([Ca(2+)](i)) and cAMP in the distal colon of suckling, weanling and adult rats. In the presence of tetrodotoxin, immature colon of suckling and weanling rats displayed higher potency (EC(50)) of 5-HT to stimulate Cl(-) secretion, whereas the potency of histamine was not changed during development. The potency of bethanechol was reduced during weaning and partially restored in adulthood. 5-HT increased cAMP level similarly in both neonatal and adult colonic crypts, but the adults had higher basal level of cAMP than suckling rats. Also the effect of bethanechol on [Ca(2+)](i) was independent of colonic maturation. The results suggest that colonic Cl(-) secretion displays developmental changes of regulation depending on the non-neural secretagogue-signalling pathway and that these developmental changes seem to be localized somewhere outside colonocytes.

• Potential and drawbacks of EDDS-enhanced phytoextraction of copper from contaminated soils

  Authors: Michael Komárek, Aleš Vaněk, Libor Mrnka, Radka Sudová, Jiřina Száková, Václav Tejnecký, Vladislav Chrastný

  Environmental Pollution.

  Incubation and pot experiments using poplar (Populus nigra L. cv. Wolterson) were performed in order to evaluate the questionable efficiency of EDDS-enhanced phytoextraction of Cu from contaminatedIncubation and pot experiments using poplar (Populus nigra L. cv. Wolterson) were performed in order to evaluate the questionable efficiency of EDDS-enhanced phytoextraction of Cu from contaminated soils. Despite the promising conditions of the experiment (low contamination of soils with a single metal with a high affinity for EDDS, metal tolerant poplar species capable of producing high biomass yields, root colonization by mycorrhizal fungi), the phytoextraction efficiency was not sufficient. The EDDS concentrations used in this study (3 and 6 mmol kg−1) enhanced the mobility (up to a 100-fold increase) and plant uptake of Cu (up to a 65-fold increase). However, despite EDDS degradation and the competition of Fe and Al for the chelant, Cu leaching cannot be omitted during the process. Due to the low efficiency, further research should be focused on other environment-friendly methods of soil remediation.

• Age-dependent effect of secretagogues during colonic maturation

  Authors: Libor Mrnka, Sergej Beskid, Oksana Sevastyanova, Jana Bryndová, Jiří Pácha

  European Journal of Pharmacology.

  Intestinal secretory response is altered during colonic development. The aim of this report was to study the developmental changes of the Ca2+- and cAMP-induced regulatory pathways with specialIntestinal secretory response is altered during colonic development. The aim of this report was to study the developmental changes of the Ca2+- and cAMP-induced regulatory pathways with special attention to the direct and indirect effect of secretagogues on the colonic epithelium. We investigated the effect of bethanechol, 5-hydroxytryptamine (5-HT), and histamine on Cl− secretion and stimulation of intracellular Ca2+ ([Ca2+]i) and cAMP in the distal colon of suckling, weanling and adult rats. In the presence of tetrodotoxin, immature colon of suckling and weanling rats displayed higher potency (EC50) of 5-HT to stimulate Cl− secretion, whereas the potency of histamine was not changed during development. The potency of bethanechol was reduced during weaning and partially restored in adulthood. 5-HT increased cAMP level similarly in both neonatal and adult colonic crypts, but the adults had higher basal level of cAMP than suckling rats. Also the effect of bethanechol on [Ca2+]i was independent of colonic maturation. The results suggest that colonic Cl− secretion displays developmental changes of regulation depending on the non-neural secretagogue-signalling pathway and that these developmental changes seem to be localized somewhere outside colonocytes.