Microelectrode Measurements in Stromatolites: Unraveling the Earth's Past?

2002 ◽  
pp. 265-282 ◽  
Author(s):  
Pieter T. Visscher ◽  
Shelley E. Hoeft ◽  
Tonna-Marie L. Surgeon ◽  
Daniel R. Rogers ◽  
Brad M. Bebout ◽  
...  
Keyword(s):  
Microelectrode Measurements

Mutation of a single amino acid converts the human water channel aquaporin 5 into an anion channel

2013 ◽  
Vol 305 (6) ◽  
pp. C663-C672 ◽  
Author(s):  
Xue Qin ◽  
Walter F. Boron
Keyword(s):  
Water Channel ◽  
Anion Channel ◽  
Single Amino Acid ◽  
Side Chain ◽  
Wild Type ◽  
Aquaporin 5 ◽  
Anion Conductance ◽  
Electrode Voltage ◽  
Microelectrode Measurements ◽  
Positively Charged

Aquaporin 6 (AQP6) is unique among mammalian AQPs in being an anion channel with negligible water permeability. However, the point mutation Asn60Gly converts AQP6 from an anion channel into a water channel. In the present study of human AQP5, we mutated Leu51 (corresponding to residue 61 in AQP6), the side chain of which faces the central pore. We evaluated function in Xenopus oocytes by two-electrode voltage clamp, video measurements of osmotic H2O permeability ( Pf), microelectrode measurements of surface pH (pHS) to assess CO2 permeability, and surface biotinylation. We found that AQP5-L51R does not exhibit the H2O or CO2 permeability of the wild-type protein but instead has a novel p-chloromercuribenzene sulfonate (pCMBS)-sensitive current. The double mutant AQP5-L51R/C182S renders the conductance insensitive to pCMBS, demonstrating that the current is intrinsic to AQP5. AQP5-L51R has the anion permeability sequence I− > NO3− ≅ NO2− > Br− > Cl− > HCO3− > gluconate. Of the other L51 mutants, L51T (polar uncharged) and L51V (nonpolar) retain H2O and CO2 permeability and do not exhibit anion conductance. L51D and L51E (negatively charged) have no H2O or CO2 permeability. L51K (positively charged) has an intermediate H2O and CO2 permeability and anion conductance. L51H is unusual in having a relatively low CO2 permeability and anion conductance, but a moderate Pf. Thus, positively charged mutations of L51 can convert AQP5 from a H2O/CO2 channel into an anion channel. However, the paradoxical effect of L51H is consistent with the hypothesis that CO2, in part, takes a pathway different from H2O through AQP5.

Microelectrode measurements of pericellular PO2 in erythropoietin-producing human hepatoma cell cultures

1993 ◽  
Vol 265 (5) ◽  
pp. C1266-C1270 ◽  
Author(s):  
M. Wolff ◽  
J. Fandrey ◽  
W. Jelkmann
Keyword(s):  
Cell Cultures ◽  
Hepatoma Cell ◽  
Gas Diffusion ◽  
Human Hepatoma ◽  
Human Hepatoma Cell ◽  
Hepatoma Cell Lines ◽  
Vitro Model ◽  
O2 Supply ◽  
Microelectrode Measurements

On the basis of Fick's law of gas diffusion, it has been proposed that cells in conventional monolayer cultures may be severely hypoxic. Because knowledge of the cellular O2 availability is important for the interpretation of biochemical and toxicological cell culture work, microelectrode measurements of the pericellular PO2 were carried out using the erythropoietin (Epo)-producing human hepatoma cell lines Hep G2 and Hep 3B as an in vitro model. In confluent hepatoma cultures grown in polystyrene dishes and incubated in air with 5% CO2, the pericellular steady-state PO2 was < 1 mmHg. The rates of the production of immunoreactive Epo and lactate were high due to a misproportion between O2 supply and O2 requirements. Epo production decreased when shaken instead of static cultures were studied, or when the O2 concentration in the gas atmosphere was increased gradually up to 95%. In cultures grown on gas-permeable supports, pericellular and gas PO2 values were very similar, with increased Epo production at lowered PO2. In agreement with mathematical models, our experimental data make PO2 measurements desirable for studies of O2-dependent biological functions in cell cultures.

scholarly journals Electrophysiological evidence for light-activated cation transport in calcifying corals

2019 ◽  
Vol 286 (1896) ◽  
pp. 20182444 ◽  
Author(s):  
Isabelle Taubner ◽  
Marian Y. Hu ◽  
Anton Eisenhauer ◽  
Markus Bleich
Keyword(s):  
Ion Transport ◽  
Ussing Chamber ◽  
Light Response ◽  
Coral Host ◽  
Hermatypic Coral ◽  
Stylophora Pistillata ◽  
Hermatypic Corals ◽  
Net Flux ◽  
Endosymbiotic Algae ◽  
Microelectrode Measurements

Light has been demonstrated to enhance calcification rates in hermatypic coral species. To date, it remains unresolved whether calcifying epithelia change their ion transport activity during illumination, and whether such a process is mediated by the endosymbiotic algae or can be controlled by the coral host itself. Using a modified Ussing chamber in combination with H + sensitive microelectrode measurements, the present work demonstrates that light triggers the generation of a skeleton positive potential of up to 0.9 mV in the hermatypic coral Stylophora pistillata . This potential is generated by a net flux of cations towards the skeleton and reaches its maximum at blue (450 nm) light. The effects of pharmacological inhibitors targeting photosynthesis 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and anion transport 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) were investigated by pH microelectrode measurements in coral tissues demonstrating a rapid decrease in tissue pH under illumination. However, these inhibitors showed no effect on the electrophysiological light response of the coral host. By contrast, metabolic inhibition by cyanide and deoxyglucose reversibly inhibited the light-induced cation flux towards the skeleton. These results suggest that ion transport across coral epithelia is directly triggered by blue light, independent of photosynthetic activity of algal endosymbionts. Measurements of this very specific and quantifiable physiological response can provide parameters to identify photoreception mechanisms and will help to broaden our understanding of the mechanistic link between light stimulation and epithelial ion transport, potentially relevant for calcification in hermatypic corals.

Monitoring the influence of toxic compounds on microbial denitrifying biofilm processes

2003 ◽  
Vol 47 (5) ◽  
pp. 211-216 ◽  
Author(s):  
J. Li ◽  
P.L. Bishop
Keyword(s):  
Organic Compound ◽  
Redox Potential ◽  
Organic Compounds ◽  
Acid Orange 7 ◽  
Toxic Compounds ◽  
Acid Orange ◽  
Anoxic Layer ◽  
Anaerobic Zone ◽  
Microelectrode Measurements

Microelectrode measurements were conducted to obtain nitrate, pH and redox potential profiles within anoxic denitrifying biofilms. The influence of a toxic organic compound (acid orange 7) on biofilm microprofiles was also monitored using microelectrodes. The data provide evidence that the denitrifying biofilms were stratified into an anoxic layer and an anaerobic layer. The anaerobic zone might provide a niche for the biodegradation of recalcitrant organic compounds in biofilms. It was found that acid orange 7 and its biodegradation byproducts had only a slight impact on biofilm nitrate, pH and redox potential profiles.

Sodium compartmentalization in single muscle fibers of the giant barnacle

1970 ◽  
Vol 48 (2) ◽  
pp. 139-146 ◽  
Author(s):  
R. D. Allen ◽  
J. A. M. Hinke
Keyword(s):  
Muscle Fibers ◽  
Flux Analysis ◽  
Single Muscle ◽  
Activity Measurements ◽  
Microelectrode Measurements

The influx and efflux of 22Na+ was measured in single muscle fibers of the giant barnacle, Balanus nubilus. These experiments show that intracellular Na+ is divided into two compartments. A rapidly exchanging compartment, identified as myoplasmic free Na+, was evident in both influx and efflux experiments. A very slowly exchanging compartment was evident only in the influx experiments. The size of the rapidly exchanging compartment, expressed as the percentage of total intracellular Na, was estimated from the 22Na+ influx experiments and from intracellular Na+ activity measurements made with Na+-specific glass microelectrodes. Influx measurements showed 58.5% free Na+, and Na+ microelectrode measurements showed 51.6% free Na+. Both the 22Na+ flux analysis and Na+ activity measurements indicate at least two compartments for intracellular Na+.

scholarly journals Influences of Infaunal Burrows on the Community Structure and Activity of Ammonia-Oxidizing Bacteria in Intertidal Sediments

2006 ◽  
Vol 73 (4) ◽  
pp. 1341-1348 ◽  
Author(s):  
Hisashi Satoh ◽  
Yoshiyuki Nakamura ◽  
Satoshi Okabe
Keyword(s):  
16S Rrna ◽  
16S Rrna Gene ◽  
Gene Copy ◽  
Sediment Surface ◽  
Intertidal Sediment ◽  
Rrna Gene ◽  
Ammonia Oxidizing Bacteria ◽  
Intertidal Sediments ◽  
Burrow Wall ◽  
Microelectrode Measurements

ABSTRACT Influences of infaunal burrows constructed by the polychaete (Tylorrhynchus heterochaetus) on O2 concentrations and community structures and abundances of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in intertidal sediments were analyzed by the combined use of a 16S rRNA gene-based molecular approach and microelectrodes. The microelectrode measurements performed in an experimental system developed in an aquarium showed direct evidence of O2 transport down to a depth of 350 mm of the sediment through a burrow. The 16S rRNA gene-cloning analysis revealed that the betaproteobacterial AOB communities in the sediment surface and the burrow walls were dominated by Nitrosomonas sp. strain Nm143-like sequences, and most of the clones in Nitrospira-like NOB clone libraries of the sediment surface and the burrow walls were related to the Nitrospira marina lineage. Furthermore, we investigated vertical distributions of AOB and NOB in the infaunal burrow walls and the bulk sediments by real-time quantitative PCR (Q-PCR) assay. The AOB and Nitrospira-like NOB-specific 16S rRNA gene copy numbers in the burrow walls were comparable with those in the sediment surfaces. These numbers in the burrow wall at a depth of 50 to 55 mm from the surface were, however, higher than those in the bulk sediment at the same depth. The microelectrode measurements showed higher NH4 + consumption activity at the burrow wall than those at the surrounding sediment. This result was consistent with the results of microcosm experiments showing that the consumption rates of NH4 + and total inorganic nitrogen increased with increasing infaunal density in the sediment. These results clearly demonstrated that the infaunal burrows stimulated O2 transport into the sediment in which otherwise reducing conditions prevailed, resulting in development of high NH4 + consumption capacity. Consequently, the infaunal burrow became an important site for NH4 + consumption in the intertidal sediment.

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