Ca-sensitive sodium absorption in the colon of Xenopus laevis

Summary Transepithelial electrogenic Na transport (I_Na) was investigated in the colon of the frog Xenopus laevis with electrophysiological methods in vitro. The short circuit current (I_sc) of the voltage-clamped tissue was 24.2±1.8 A·cm^-2 (n=10). About 60% of this current was generated by electrogenic Na transport. Removal of Ca²⁺ from the mucosal Ringer solution stimulated I_Na by about 120%. I_Na was not blockable by amiloride (0.1 mmol·l^-1), a specific Na-channel blocker in epithelia, but a fully and reversible inhibition was achieved by mucosal application of 1 mmol·l^-1 lanthanum (La^3-). No Na-self-inhibition was found, because I_Na increased linearly with the mucosal Na concentration. A stimulation of I_Na by antidiuretic hormones was not possible. The analysis of fluctuations in the short circuit current (noise analysis) indicated that Na ions pass the apical cell membrane via a Ca-sensitive ion channel. The results clearly demonstrate that in the colon of Xenopus laevis Na ions are absorbed through Ca-sensitive apical ion channels. They differ considerably in their properties and regulation from the amiloride-sensitive Na channel which is typically found in the colon of vertebrates.Abbreviations G _T transepithelial conductance - I _sc short circuit current - I _Na transepithelial Na-current - m mucosal - s serosal - PDS power density spectrum - f frequency - f _c corner frequency of the Lorentzian component of the PDS - S(f) power density of the Lorentzian component of the PDS - S_o plateau value of the Lorentzian component of the PDS     

The effects of N-alkylmaleimides on the activity of rat liver glucose 6-phosphatase.

A series of N-alkylmaleimides has been synthesized and used to investigate the thiol groups that are essential for the activity of rat liver microsomal glucose 6-phosphatase. All of the N-alkylmaleimides inactivated glucose 6-phosphatase when preincubated with microsomes (microsomal fractions) at pH 6.5 and 30 degrees C. When enzyme activity was assayed in intact microsomes, the inactivation was non-linear with respect time, showing an initial rapid phase followed by a slower secondary phase. During the initial rapid phase the inactivation may apparently be completely reversed by disrupting the microsomal membrane with detergent. However, after longer exposure to N-alkylmaleimides the reversal is no longer complete. This observation was explained by the results obtained from studying the inactivation in detergent-disrupted microsomes. In this case glucose 6-phosphatase was also completely inactivated, but much more slowly than was seen in intact microsomes, and the process was linear with respect to time. When assayed in both intact and detergent-disrupted microsomes, glucose 6-phosphatase inactivation was dependent on the number of carbon atoms in the alkyl side chain of the N-alkylmaleimides; this dependence was much more marked in disrupted microsomes. Analysis of the data showed that in neither case was there a saturating effect at high concentrations of maleimide. The data have been interpreted to suggest that there are are least two thiol groups essential for activity located in two separate non-polar regions of the membrane-enzyme system. The conclusions are discussed in the light of the current model for the microsomal glucose 6-phosphatase system.     

Fatal Invasive Pulmonary Aspergillosis in COVID-19 Patient with Acute Myeloid Leukemia in Iran

Mycopathologia - Although patients with severe immunodeficiency and hematological malignancies has been considered at highest risk for invasive fungal infection, patients with severe pneumonia due...     

Involvement of Microorganisms in the Formation of Carbonate Speleothems in the Cervo Cave (L'Aquila-Italy)

Much is known about the bacterial precipitation of carbonate rocks, but comparatively little is known about the involvement of microbes in the formation of secondary mineral structures in caves. We hypothesized that bacteria isolated from calcareous stalactites, which are able to mediate CaCO₃ precipitation in vitro, play a role in the formation of carbonate speleothems. We collected numerous cultivable calcifying bacteria from calcareous speleothems from Cervo cave, implying that their presence was not occasional. The relative abundance of calcifying bacteria among total cultivable microflora was found to be related to the calcifying activity in the stalactites. We also determined the δ ¹³C and δ ¹⁸ O values of the Cervo cave speleothems from which bacteria were isolated and of the carbonates obtained in vitro to determine whether bacteria were indeed involved in the formation of secondary mineral structures. We identified three groups of biological carbonates produced in vitro at 11°C on the basis of their carbon isotopic composition: carbonates with δ ¹³C values (a) slightly more positive, (b) more negative, and (c) much more negative than those of the stalactite carbonates. The carbonates belonging to the first group, characterized by the most similar δ ¹³C values to stalactites, were produced by the most abundant strains. Most of calcifying isolates belonged to the genus Kocuria. Scanning electron microscopy showed that dominant morphologies of the bioliths were sherulithic with fibrous radiated interiors. We suggest a mechanism of carbonate crystal formation by bacteria.     

Brief communication: Evolution of a specific O allele (O1vG542A) supports unique ancestry of Native Americans

In this study, we explore the geographic and temporal distribution of a unique variant of the O blood group allele called O1v^G542A, which has been shown to be shared among Native Americans but is rare in other populations. O1v^G542A was previously reported in Native American populations in Mesoamerica and South America, and has been proposed as an ancestry informative marker. We investigated whether this allele is also found in the Tlingit and Haida, two contemporary indigenous populations from Alaska, and a pre‐Columbian population from California. If O1v^G542A is present in Na‐Dene speakers (i.e., Tlingits), it would indicate that Na‐Dene speaking groups share close ancestry with other Native American groups and support a Beringian origin of the allele, consistent with the Beringian Incubation Model. If O1v^G542A is found in pre‐Columbian populations, it would further support a Beringian origin of the allele, rather than a more recent introduction of the allele into the Americas via gene flow from one or more populations which have admixed with Native Americans over the past five centuries. We identified this allele in one Na‐Dene population at a frequency of 0.11, and one ancient California population at a frequency of 0.20. Our results support a Beringian origin of O1v^G542A, which is distributed today among all Native American groups that have been genotyped in appreciable numbers at this locus. This result is consistent with the hypothesis that Na‐Dene and other Native American populations primarily derive their ancestry from a single source population. Am J Phys Anthropol 151:649–657, 2013. © 2013 Wiley Periodicals, Inc.     

Secretory Expression of a Chimeric Peptide in Lactococcus lactis: Assessment of its Cytotoxic Activity and a Deep View on Its Interaction with Cell-Surface Glycosaminoglycans by Molecular Modeling

Probiotics and Antimicrobial Proteins - Nowadays, cancer remains a major cause of death affecting millions of people. Currently, the antimicrobial peptides (AMPs) as potent anticancer therapeutic...     

Investigation of the dimerization of proteins from the epidermal growth factor receptor family by single wavelength fluorescence cross-correlation spectroscopy

Single wavelength fluorescence cross-correlation spectroscopy (SW-FCCS), introduced to study biomolecular interactions, has recently been reported to monitor enzyme activity by using a newly developed fluorescent protein variant together with cyan fluorescent protein. Here, for the first time to our knowledge, SW-FCCS is applied to detect interactions between membrane receptors in vivo by using the widely used enhanced green fluorescent protein and monomeric red fluorescent protein. The biological system studied here is the epidermal growth factor/ErbB receptor family, which plays pivotal roles in the development of organisms ranging from worms to humans. It is widely thought that a ligand binds to the monomeric form of the receptor and induces its dimeric form for activation. By using SW-FCCS and F?rster resonance energy transfer, we show that the epidermal growth factor receptor and ErbB2 have preformed homo- and heterodimeric structures on the cell surface and quantitation of dimer fractions is performed by SW-FCCS. These receptors are major targets of anti-cancer drug development, and the receptors' homo- and heterodimeric structures are relevant for such developments.