Fast material disintegration of cement concrete in the exterior

Over the recent years the amount of fast destruction defects of cement paste matrix has increased markedly for exposed concrete structures of highway and airport pavements. The accelerated destruction of silicate structure is unusual due to its irregular occurrence. It only occurs at 30 to 50% of newly built pavements (in continuous segments). The issue is applicable to loaded as well as unloaded pavements. Detailed diagnostics found that the probable cause is based on concurrently occurring expansive reactions in capillaries, cracks and pores in the cement paste matrix. In defect spots the presence of several expansive substances was proven, wherein the biggest question poses the unexpectedly high potassium concentration. Potassium is only contained at best in trace amounts in road concrete input components in the Czech Republic. Neither existing regulations nor standards sufficiently deal with this type of defects of cement concretes. If they mention the existence of this issue at all, they are just limited to recommendations. Since the modification of the existing commercially produced cements to pavements is still improbable, the solutions to this issue seem problematic.

Rapid adaptation to elevated extracellular potassium in the pyloric circuit of the crab, Cancer borealis

Solutions with elevated extracellular potassium are commonly used as a depolarizing stimulus. We studied the effects of high potassium concentration ([K+]) on the pyloric circuit of the crab stomatogastric ganglion. A 2.5-fold increase in extracellular [K+] caused a transient loss of activity that was not due to depolarization block, followed by a rapid increase in excitability and recovery of spiking within minutes. This suggests that changing extracellular potassium can have complex and nonstationary effects on neuronal circuits.

Vascular Occlusion Restores Endothelium-Dependent Effects of Adenosine Previously Diminished by Diabetes: The Preliminary Report

The aim of this study was to investigate the effect of adenosine in non-occluded or occluded femoral arteries (FA) that were isolated from healthy or diabetic Wistar rats. Determining the role of endothelium, and a transmembrane flow of potassium ions in adenosine actions were also of interest. Diabetes was experimentally induced by alloxan, while the vascular occlusion was performed for 45 min on randomly selected FA. Vascular tone changes were continuously recorded. Selected markers of endothelial dysfunction were measured in animal serum. Thus, adenosine produced a concentration-dependent relaxation of rat FA, which was endothelium-dependent, too, except in a group of diabetic animals. Moreover, serum asymmetric dimethylarginine (ADMA) levels were higher in diabetic animals, thus reflecting endothelial dysfunction (ED). Still, an occlusion of FA enhanced the relaxation effect of adenosine in endothelium-intact rings from diabetic animals. Oppositely, in the presence of high potassium concentration in the buffer, adenosine-induced relaxation was significantly reduced in all of the investigated groups/subgroups. These results suggest that in diabetic animals, an occlusion of FA most probably reversed adenosine-induced relaxation from endothelium-independent into an endothelium-dependent relaxation, thus indicating the possible protective mechanism against ischemic episodes of FA in the presence of diabetes.

Effect of Imperatorin on the Spontaneous Motor Activity of Rat Isolated Jejunum Strips

Imperatorin, a psoralen-type furanocoumarin, is a potent myorelaxant agent acting as a calcium antagonist on vascular smooth muscle. Its effects on other types of smooth muscle remain unknown. Therefore, the aim of this study was to investigate the hypothesized myorelaxant effect of imperatorin on gut motor activity and, possibly, to define the underlying mechanism of action. Imperatorin was made available for pharmacological studies from the fruits of the widely availableAngelica officinalisthrough the application of high-performance countercurrent chromatography (HPCCC). Imperatorin generated reversible relaxation of jejunum strips dose-dependently (1–100 μM). At 25 and 50 μM, imperatorin caused relaxation comparable to the strength of the reaction induced by isoproterenol (Isop) at 0.1 μM. The observed response resulted neither from the activation of soluble guanylate cyclase, nor fromβ-adrenoreceptor involvement, nor from Ca2+-activated potassium channels. Imperatorin relaxed intestine strips precontracted with high potassium concentration, attenuated the force and duration of K+-induced contractions, and modulated the response of jejunum strips to acetylcholine. The results suggest that imperatorin probably interacts with various Ca2+influx pathways in intestine smooth muscle. The types of some calcium channels involved in the activity of imperatorin will be examined in a subsequent study.

Gene expression and cellular localization of ROMKs in the gills and kidney of Mozambique tilapia acclimated to fresh water with high potassium concentration

Regulation of plasma K+ levels in narrow ranges is vital to vertebrate animals. Since seawater (SW) teleosts are loaded with excess K+, they constantly excrete K+ from the gills. However, the K+ regulatory mechanisms in freshwater (FW)-acclimated teleosts are still unclear. We aimed to identify the possible K+ regulatory mechanisms in the gills and kidney, the two major osmoregulatory organs, of FW-acclimated Mozambique tilapia ( Oreochromis mossambicus). As a potential molecular candidate for renal K+ handling, a putative renal outer medullary K+ channel (ROMK) was cloned from the tilapia kidney and tentatively named “ROMKb”; another ROMK previously cloned from the tilapia gills was thus renamed “ROMKa”. The fish were acclimated to control FW or to high-K+ (H-K) FW for 1 wk, and we assessed physiological responses of tilapia to H-K treatment. As a result, urinary K+ levels were slightly higher in H-K fish, implying a role of the kidney in K+ excretion. However, the mRNA expression levels of both ROMKa and ROMKb were very low in the kidney, while that of K+/Cl− cotransporter 1 (KCC1) was robust. In the gills, ROMKa mRNA was markedly upregulated in H-K fish. Immunofluorescence staining showed that branchial ROMKa was expressed at the apical membrane of type I and type III ionocytes, and the ROMKa immunosignals were more intense in H-K fish than in control fish. The present study suggests that branchial ROMKa takes a central role for K+ regulation in FW conditions and that K+ excretion via the gills is activated irrespective of environmental salinity.