K-Cl cotransport, pH, and role of Mg in volume-clamped low-K sheep erythrocytes: three equilibrium states

1994 ◽  
Vol 266 (1) ◽  
pp. C95-C103 ◽  
Author(s):  
P. K. Lauf ◽  
A. Erdmann ◽  
N. C. Adragna
Keyword(s):  
Cell Volume ◽  
Ph Effect ◽  
Ph Dependence ◽  
Maximum Velocity ◽  
Major Change ◽  
Small Displacement ◽  
Reversal Point ◽  
Flux Reversal ◽  
Low K

Ouabain-resistant K efflux and Rb influx in Cl and NO3 media were studied in volume-clamped low-K (LK) sheep red blood cells (SRBC) with normal and experimentally reduced cytoplasmic Mg (Mgi) levels as function of pH and at 37 degrees C. Sucrose was added to solutions with constant ionic strength and variable pH to maintain normal cell volume. Cl-dependent ouabain-resistant K(Rb) fluxes (K-Cl cotransport) at unity relative cell volume exhibited a maximum at pH approximately 7 in normal-Mgi LK cells consistent with the apparent acid pH activation reported for human erythrocytes. However, in LK SRBC with Mgi lowered by A-23187 and an external Mg chelator, K(Rb)-Cl cotransport was reversibly activated as the pH was raised from 6.5 to 9. The alkaline pH effect on Cl-dependent Rb influx in low-Mgi LK SRBC was due to a 10-fold rise in the maximum velocity values without a major change in the Km values. The pH dependence of the experimental flux reversal point, i.e., the extracellular Rb concentration at which no net K-Cl cotransport occurs, approximately paralleled that of the flux reversal point predicted from the ratio of the ion products, in both control and low-Mgi LK cells, albeit with a small displacement to higher extracellular Rb concentration at all pH values. The kinetic data can be explained by a general minimum three-state equilibrium in which deprotonation recruits transporters from a resting R state into the active A state modified by Mgi to an inactive I state.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals A thermodynamic study of electroneutral K-Cl cotransport in pH- and volume-clamped low K sheep erythrocytes with normal and low internal magnesium.

1996 ◽  
Vol 108 (4) ◽  
pp. 341-350 ◽  
Author(s):  
P K Lauf ◽  
N C Adragna
Keyword(s):  
Cell Volume ◽  
Potential Gradient ◽  
Ionophore A23187 ◽  
Flux Reversal ◽  
Internal Ph ◽  
Before And After ◽  
Disulfonic Stilbene ◽  
Constant Cell ◽  
K Concentration ◽  
Low K

Swelling-induced human erythrocyte K-Cl cotransport is membrane potential independent and capable of uphill transport. However, a complete thermodynamic analysis of basal and stimulated K-Cl cotransport, at constant cell volume, is missing. This study was performed in low K sheep red blood cells before and after reducing cellular free Mg into the nanomolar range with the divalent cation ionophore A23187 and a chelator, an intervention known to stimulate K-Cl cotransport. The anion exchange inhibitor 4,4'diisothiocyanato-2,2'disulfonic stilbene was used to clamp intracellular pH and Cl or NO3 concentrations. Cell volume was maintained constant as external and internal pH differed by more than two units. K-Cl cotransport was calculated from the K effluxes and Rb (as K congener) influxes measured in Cl and NO3, at constant internal K and external anions, and variable concentrations of extracellular Rb and internal anions, respectively. The external Rb concentration at which net K-Cl cotransport is zero was defined as flux reversal point which changed with internal pH and hence Cl. Plots of the ratio of external Rb concentrations corresponding to the flux reversal points and the internal K concentration versus the ratio of the internal and external Cl concentrations (i.e., the Donnan ratio of the transported ions) yielded slopes near unity for both control and low internal Mg cells. Thus, basal as well as low internal Mg-stimulated net K-Cl cotransport depends on the electrochemical potential gradient of KCl.

scholarly journals Proton transfer in the mechanism of polyadenylate polymerase

2009 ◽  
Vol 420 (2) ◽  
pp. 229-242 ◽  
Author(s):  
Paul B. Balbo ◽  
Andrew Bohm
Keyword(s):  
Proton Transfer ◽  
Catalytic Mechanism ◽  
Ph Dependence ◽  
Maximum Velocity ◽  
Forward Reaction ◽  
Rate Determining Step ◽  
Steady State Kinetic ◽  
Ph Range ◽  
Solvent Isotope

PAP (polyadenylate polymerase) is the template-independent RNA polymerase responsible for synthesis of the 3′ poly(A) tails of mRNA. To investigate the role of proton transfer in the catalytic mechanism of PAP, the pH dependence of the steady-state kinetic parameters of yeast PAP were determined for the forward (adenyl transfer) and reverse (pyrophosphorolysis) reactions. The results indicate that productive formation of an enzyme–RNA–MgATP complex is pH independent over a broad pH range, but that formation of an active enzyme–RNA–MgPPi complex is strongly pH dependent, consistent with the production of a proton on the enzyme in the forward reaction. The pH dependence of the maximum velocity of the forward reaction suggests two protonic species are involved in enzyme catalysis. Optimal enzyme activity requires one species to be protonated and the other deprotonated. The deuterium solvent isotope effect on Vmax is also consistent with proton transfer involved in catalysis of a rate-determining step. Finally, pKa calculations of PAP were performed by the MCCE (multiconformational continuum electrostatic) method. Together, the data support that the protonation of residues Lys215 and Tyr224 exhibit co-operativity that is important for MgATP2− and MgPPi2− binding/dissociation, and suggest these residues function in electrostatic, but not in general acid, catalysis.

Liver cell hydration and integrin signaling

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Michele Bonus ◽  
Dieter Häussinger ◽  
Holger Gohlke
Keyword(s):  
Cell Volume ◽  
Liver Cell ◽  
Cell Function ◽  
The Other ◽  
Signaling Cascades ◽  
Integrin Signaling ◽  
Volume Changes ◽  
The One ◽  
And Oxidative Stress

Abstract Liver cell hydration (cell volume) is dynamic and can change within minutes under the influence of hormones, nutrients, and oxidative stress. Such volume changes were identified as a novel and important modulator of cell function. It provides an early example for the interaction between a physical parameter (cell volume) on the one hand and metabolism, transport, and gene expression on the other. Such events involve mechanotransduction (osmosensing) which triggers signaling cascades towards liver function (osmosignaling). This article reviews our own work on this topic with emphasis on the role of β1 integrins as (osmo-)mechanosensors in the liver, but also on their role in bile acid signaling.

Variable Ramp Rate Breakdown Experiments and the Role of Metal Injection in Low- $k$ Dielectrics

2011 ◽  
Vol 58 (12) ◽  
pp. 4354-4360 ◽  
Author(s):  
Joel L. Plawsky ◽  
Juan Borja ◽  
Brian Williams ◽  
Michael J. Riley ◽  
William N. Gill
Keyword(s):  
Ramp Rate ◽  
Low K

PHYSIATRY DURING COVID-19: A SURVEY BASED ANALYSIS

2021 ◽  
pp. 48-51
Author(s):  
Mrinal Joshi ◽  
Aayushi Choudhary
Keyword(s):  
Social Media ◽  
Healthy Lifestyle ◽  
Major Change ◽  
Nationwide Survey ◽  
Lifestyle Changes ◽  
Health Crisis ◽  
Rehabilitation Programs ◽  
Practice Patient ◽  
Musculoskeletal Rehabilitation

Introduction: The declaration of COVID 19 pandemic by WHO on 11th March 2020, is the dening global health crisis of the past 100 years. The following Nationwide survey was conducted to ascertain the sea changes this pandemic has brought in the physiatrist practice, patient management and preparing oneself to the challenges of rehabilitation in the POST COVID world. The survey covers the role and importance of social media in medical education and consultation in a POST COVID world. It also sheds light on the nancial implications and personal lifestyle changes that physiatrists are witnessing. A Google form comprising of 74 questions, divided in 3 se Material &Methods: ctions, was used to gather the requisite data on :- A) PRECOVID practice, management and lifestyle; B) Life during COVID pandemic; and C) Anticipated changes in POST COVID era. The survey was circulated to 400 physiatrist via various interactive groups who have been practicing either independently or in govt setups and associated hospitals nationwide. They were requested to submit their responses in a period of 30 days. In PRECOVID era an average Result: physiatrist was nely balancing his profession, personal lifestyle, learning and recreation. The LOCKDOWN clamped their practice which lead to nancial drought but hardly made a dent in productivity by engaging in webinars, reading and researching. The POST COVID time demands implementation of newer safety protocols like changes in setup, regulating the patient trafc, limiting daily procedures, engaging in distance learning through virtual conferences, maintaining a healthy lifestyle and constructing proper protocols for pulmonary, neurological and musculoskeletal rehabilitation programs for patients post recovery from COVID19, especially the patients weaning from ventilators. Conclusion: The effect of COVID19 demands major change in physiatrist professional practice like limiting consultation, following safety protocols, COVID testing, preparing consolidated program for POSTCOVID sequel. Social media is rightly poised to be a major tool for education, consultation, marketing and awareness. The role of teleconsultation needs to be reprised, recognised and regularised. Webinars and virtual conferences will nd more takers in future.

The role of ion content and cell volume in insulin action

1994 ◽  
Vol 22 (2) ◽  
pp. 516-522 ◽  
Author(s):  
Loranne Agius ◽  
Matthew Peak ◽  
Guy Beresford ◽  
Molham Al-Habori ◽  
Trevor H. Thomas
Keyword(s):  
Cell Volume ◽  
Insulin Action ◽  
Ion Content

Functional role of amino terminus in ClC-3 chloride channel regulation by phosphorylation and cell volume

2006 ◽  
Vol 187 (1-2) ◽  
pp. 5-19 ◽  
Author(s):  
C. F. Rossow ◽  
D. Duan ◽  
W. J. Hatton ◽  
F. Britton ◽  
J. R. Hume ◽  
...  
Keyword(s):  
Cell Volume ◽  
Chloride Channel ◽  
Functional Role ◽  
Amino Terminus ◽  
Channel Regulation

scholarly journals Moisture Induced Degradation of Porous Low-k Materials

2006 ◽  
Vol 914 ◽  
Author(s):  
Mikhail Baklanov ◽  
David O'Dwyer ◽  
Adam M Urbanowicz ◽  
Quoc Toan Le ◽  
Steven Demuynck ◽  
...  
Keyword(s):  
Water Film ◽  
Internal Surface ◽  
Hydrophobic Surface ◽  
Adsorbed Water ◽  
Bulk Water ◽  
Oh Groups ◽  
Film Bulk ◽  
Low K

AbstractInteraction of moisture with porous low-k films is evaluated by using in situ ellipsometry setup. The adsorbed water amount is calculated from change of refractive index measured during the adsorption. Pristine low-k films reversibly adsorb 2 - 5% of water that reflects presence of constitutive hydrophilic centrums. Plasma and thermal treatments increase the number of hydrophilic centrums. Once the amount of these centrums has reached a certain critical value sufficient to form a continuous water film, bulk water condensation is observed. Change of properties during the water adsorption in the damaged films is not fully reversible. Each additional adsorption cycle increases the dielectric function of the film because of decreasing porosity, increasing skeleton density and shrinkage. The pressure corresponding to the bulk condensation allows us to calculate internal contact angle (internal surface energy) of low-k materials. The water molecules adsorbed on separate OH groups play the role of a catalyst that hydrolyses the siloxane bridges initially present on hydrophobic surface.

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