Uni-quantal endplate currents (EPC) were recorded at mouse diaphragm neuromuscular synapse by extracellular microelectrode during motor nerve stimulation. The probability of release expressed as quantal content mo, and variability of synaptic latencies expressed as P90
were estimated in the presence of extracellular calcium ([Ca2+]o)
varying between 0.2 and 0.6 mM in the bathing solution. At 0.2 mM [Ca2+]o, mo was low (0.10) and many of long-latency EPCs were present during the late phase of the release (P90 = 2.44 ms). No change in mo was found when [Ca2+]o was 0.3 mM, but P90
decreased by 39 %. For latency shortening, saturating concentration of [Ca2+]o was 0.4 mM, when P90 was 1.49 ms and latencies did not further change at 0.5 and 0.6 mM [Ca2+]o. In the latter concentrations, however, an increase of mo was still observed. It can be concluded that the early phase of the secretion did not significantly change when [Ca2+]o was raised and that only the late phase of the release depends on extracellular
calcium up to 0.4 mM.
Exocytotic machinery in neuronal and endocrine tissues is sensitive to changes in intracellular Ca2+ concentration. Endocrine cell models, that are most frequently used to study the mechanisms of regulated exocytosis, are pancreatic beta cells, adrenal chromaffin cells and pituitary cells. To reliably study the Ca2+ sensitivity in endocrine cells, accurate and fast determination of Ca2+ dependence in each tested cell is required. With slow photo-release it is possible to induce ramp-like increase in intracellular Ca2+ concentration ([Ca2+]i) that leads to a robust exocytotic activity. Slow increases in the [Ca2+] i revealed exocytotic phases with different Ca2+ sensitivities that have been largely masked in step-like flash photo-release experiments. Strikingly, in the cells of the three described model endocrine tissues (beta, chromaffin and melanotroph cells), distinct Ca2+ sensitivity ‘classes’ of secretory vesicles have been observed: a highly Ca2+ -sensitive, a medium Ca2+ -sensitive and a low Ca2+ - sensitive kinetic phase of secretory vesicle exocytosis. We discuss that a physiological modulation of a cellular activity, e.g. by activating cAMP/PKA transduction pathway, can switch the secretory vesicles between Ca2+ sensitivity classes. This significantly alters late steps in the secretory release of hormones even without utilization of an additional Ca2+ sensor protein., J. Dolenšek, M. Skelin, M. S. Rupnik., and Obsahuje bibliografii a bibliografické odkazy
Experimental and epidemiological studies suggest that calcium intake is inversely related to weight gain. Calcium of dairy origin has been shown to be more effective in promoting weight loss. However, clinical studies yielded controversial results concerning the role of calcium intake in weight change. The aim of this study was to ascertain whether the addition of calcium can affect the outcome of 3-week weight management (WM) with a hypocaloric diet characterized by a decreased calcium intake. Overweight/obese women (n=67; BMI 32.2±4.1 kg/m2; age 49.1±12.1 years) underwent a 4-week comprehensive WM program. WM included a 7 MJ/day diet resulting in a stable weight during the first week and a 4.5 MJ/day diet with mean daily calcium intake 350 mg during the second to fourth week. Participants were divided into three age- and BMI-matched groups who received placebo or calcium (500 mg/day). Calcium was administered either as carbonate or calcium of dairy origin (Lactoval). There was no significant difference in weight loss in response to WM between the placebo-treated and calcium-treated groups. However, addition of calcium to the diet resulted in a lower hunger score in the Eating Inventory as well as a decrease in plasma resistin levels. Body composition measured by bioimpedance demonstrated that added calcium leads to preservation of fat-free mass. Nevertheless, a greater loss of fat-free mass in the placebo group might be partly due to a greater loss of water., K. Kabrnová-Hlavatá, V. Hainer, M. Gojová, P. Hlavatý, V. Kopský, J. Nedvídková, M. Kunešová, J. Pařízková, M. Wagenknecht, M. Hill, J. Drbohlav., and Obsahuje bibliografii a bibliografické odkazy
Previous data concerning the action of calcium (Ca) on gastric acid secretion (GAS) indicated that calcium ions increase GAS elicited by gastrin released through a vagal mechanism, and also by a direct effect on parietal cells. Our research showed that the stimulating effect of calcium on gastric acid secretion can be antagonized by verapamil administration, which reduces gastric acid secretion . In the present study we followed the effect induced by administration of calcium and Ca-chelating agents (disodium EDTA) on gastric acid secretion and on carbonic anhydrase (CA) activity. We selected two groups of healthy volunteers: Group I (n=21) received a single i.v. dose of CaCl2 (15 mg/kg b.w.), whereas Group II (n=22) received a single i.v. dose of disodium EDTA (5 mg/kg b.w.). We determined blood calcium before and after treatment, gastric acid secretion at 2 hours, erythrocyte CA II activity, and CA IV activity in membrane parietal cells, which were isolated from gastric mucosa obtained by endoscopic biopsy. Assessment of carbonic anhydrase activity was achieved by the stopped-flow method. In Group I calcium administration increased blood calcium, HCl output, CA II and CA IV activity as compared to initial values. In Group II, disodium EDTA reduced blood calcium, HCl output, CA II and CA IV activity as compared to initial values. The results demonstrated that increased blood calcium and GAS values after calcium administration correlated with the increase of erythrocyte CA II and parietal cell CA IV activity, while disodium EDTA induced a reversed process. Our results also show that cytosolic CA II and membrane CA IV values are sensitive to calcium changes and they directly depend on these levels. Our data suggest that intra- and extracellular pH changes induced by carbonic anhydrase might account for the modulation of the physiological and pathological secretory processes in the organism., I. Puscas, M. Coltau, M. Baican, G. Domuta, A. Hecht., and Obsahuje bibliografii
The rationale for the topical application of capsaicin and other vanilloids in the treatment of pain is that such compounds selectively excite and subsequently desensitize nociceptive neurons. This desensitization is triggered by the activation of vanilloid receptors (TRPV1), which leads to an elevation in intracellular free Ca2+ levels. Depending on the vanilloid concentration and duration of exposure, the Ca2+ influx via TRPV1 desensitizes the channels themselves, which may represent not only a feedback mechanism protecting the cell from toxic Ca2+ overload, but also likely contributes to the analgesic effects of capsaicin. This review summarizes the current state of knowledge concerning the mechanisms that underlie the acute capsaicin-induced Ca2+-dependent desensitization of TRPV1 channels and explores to what extent they may contribute to capsaicin-induced analgesia. In view of the polymodal nature of TRPV1, we illustrate how the channels behave in their desensitized state when activated by other stimuli such as noxious heat or depolarizing voltages. We also show that the desensitized channel can be strongly reactivated by capsaicin at concentrations higher than those previously used to desensitize it. We provide a possible explanation for a high incidence of adverse effects of topical capsaicin and point to a need for more accurate clinical criteria for employing it as a reliable remedy., L. Vyklický, K. Nováková-Toušová, J. Benedikt, A. Samad, F. Touška, V. Vlachová., and Obsahuje bibliografii a bibliografické odkazy
We assessed the concentration of calcium, magnesium and creatinine in 2715 samples of the first morning urine. The investigation comprised the following age groups: children one, two, four, six, ten and thirteen years old, and groups of adults aged 18-35, 36-49, 50-65, 66-75, 76-85 and 86-93 years. The choice was made by random selection of participants of both sexes from diverse regions of the Czech Republic. We found the age to have a marked influence on the value of calcium, magnesium and creatinine, including urinary concentration ratios of calcium/creatinine and magnesium/crcatinine. The urinary calcium concentration was low both in the early and advanced age groups, while it reached peak values in subjects 18-35 years old. The urinary magnesium concentration was also age-dependent, with a maximum in children aged 4 years, and a subsequent decline with advancing age. The value of the ratio urinary calcium/creatinine and urinary magnesium/creatinine was highest in the youngest age group (1-4 years).
The article presents the method of the calculation of natural frequencies and mode shapes of the linear undamped rotationally periodic systems. The method is applied in the calculation of the natural vibration characteristics of the steam turbine bladed disks., Obsahuje seznam literatury, and Součástí článku je Appendix A - Solution of matrix difference equations
(str. 93-97)
Caldenal tvoří společenstva semiaridních lesů subtropického až mírného pásu střední Argentiny s dominantním druhem Prosopis caldenia. Od počátku 20. stol. byla značně exploatována kácením a využívána pro pastvu dobytka. Oheň, který zde byl přirozeným a nyní je i umělým činitelem, zásadně ovlivňuje obnovu caldenalu. Článek přináší základní údaje o tomto společenstvu a vlivu pastvy i ohně na jeho strukturu a biodiverzitu. and Caldenal is a semi-arid forest ecosystem in subtropical and temperate regions of Central Argentina, dominated by Prosopis caldenia. Since the beginning of the 20th century, Caldenal has been affected by wood harvesting and livestock grazing. Fires, both accidental and intentional, have played a key role in Caldenal regeneration. This paper describes the characteristics of these forests and addresses the effect of grazing and fire on their structure and biodiversity.
The use of electromagnetic (EM) soil moisture probes is proliferating rapidly, in two broad domains: in field and laboratory research; and in strongly practical applications such as irrigation scheduling in farms or horticultural enterprises, and hydrological monitoring. Numerous commercial EM probes are available for measurement of volumetric water content (θv), spanning a range of measurement principles, and of probe dimensions and sensing volumes. However probe calibration (i.e. the relationship of actual θv to probe electrical output) can shift, often substantially, with variations in parameters such as soil texture, organic matter content, wetness range, electrical conductivity and temperature. Hence a single-valued, manufacturer-supplied calibration function is often inadequate, forcing the user to seek an application-specific calibration. The purpose of this paper is to describe systematic procedures which probe users can use to check or re-determine the calibration of their selected probe(s). Given the wide diversity of operating principles and designs of commercially-available EM probes, we illustrate these procedures with results from our own calibrations of five different short probes (length of 5 to 20 cm). Users are strongly recommended to undertake such calibration checks, which provide both a) pre-use experience, and b) more reliable in-use data. and Používanie elektromagnetických (EM) snímačov vlhkosti pôdy sa rýchlo rozširuje tak v terénnom výskume, ako aj v laboratóriu. Sú používané v praktických aplikáciách ako je riadenie závlah na farmách a záhradách, ako aj v hydrologickom monitoringu. Pre meranie vlhkosti pôdy (θv) sú dostupné početné typy komerčných EM snímačov, založených na viacerých princípoch merania a snímače majú rozdielnu veľkosť snímaných objemov pôdy. Kalibračné krivky takýchto snímačov (t.j. závislosti medzi reálnou vlhkosťou pôdy θv a elektrickým výstupom snímača) sa môžu posúvať - niekedy podstatne - a to v závislosti od rozdielnych parametrov pôdy, ako je jej textúra, obsah organických látok, rozsah vlhkostí, elektrická vodivosť a teplota. Z toho vyplýva, že jednoznačná kalibračná krivka, dodávaná výrobcom je často neadekvátna, čo núti užívateľa snímač kalibrovať v špecifických podmienkach. Cieľom tohto príspevku je opísať procedúry, ktoré môžu byť použité užívateľmi pri rekalibrácii vybraných typov snímačov. Berúc do úvahy širokú paletu princípov EM snímačov, ilustrujeme tieto procedúry výsledkami vlastných kalibračných testov na piatich typoch krátkych snímačov (dĺžka od 5 do 20 cm). Užívateľom odporúčame rekalibráciu komerčných snímačov, ktorými získajú predbežné skúsenosti a spoľahlivejšie výsledky pri meraní vlhkosti pôdy.