scholarly journals A platform for stop flow gradient generation to investigate chemotaxis

2021 ◽  
Author(s):  
Zuyao Xiao ◽  
Audrey Nsamela ◽  
Benjamin Garlan ◽  
Juliane Simmchen
Keyword(s):  
Feedback Loop ◽  
Stopped Flow ◽  
Interdisciplinary Science ◽  
Chemical Gradients ◽  
Flow Gradient ◽  
Pressure Feedback ◽  
Gradient Generation ◽  
External Stimuli ◽  
Flow Experiments ◽  
Stop Flow

The ability of artificial microswimmers to respond to external stimuli and the mechanistical details of their origins belong to the most disputed challenges in interdisciplinary science. Therein, the creation of chemical gradients is technically challenging, because they quickly level out due to diffusion. Inspired by pivotal stopped flow experiments in chemical kinetics, we show that microfluidics gradient generation combined with a pressure feedback loop for precisely controlling the stop of the flows, can enable us to study mechanistical details of chemotaxis of artificial Janus micromotors, based on a catalytic reaction. We find that these copper Janus particles display a chemotactic motion along the concentration gradient in both, positive and negative direction and we demonstrate the mechanical reaction of the particles to small forces deviations, explaining this behaviour.

Renal tubular transport of folic acid and methotrexate in the monkey

1982 ◽  
Vol 242 (5) ◽  
pp. F484-F490 ◽  
Author(s):  
W. M. Williams ◽  
K. C. Huang
Keyword(s):  
Folic Acid ◽  
Flow Pattern ◽  
Plasma Concentrations ◽  
Free Flow ◽  
Stopped Flow ◽  
Base Line ◽  
Renal Tubular Transport ◽  
Renal Tubular ◽  
Flow Experiments ◽  
Stop Flow

The renal excretion of folic acid and methotrexate (MTX) was investigated in pentobarbital-anesthetized cynomolgus, rhesus, and AFrican green monkeys by standard clearance and stop-flow techniques. The renal clearance of folic acid was below inulin clearance at all plasma concentrations studied; the (U/P)folic/(U/P)In ratio increased from 0.26 at a concentration of 0.03 mM to a plateau value of 0.9 at concentrations above 0.2 mM, indicating net reabsorption by a saturable system. In stop-flow experiments, base-line (U/P)folic/(U/P)In ratios during free-flow periods were below 1.0, but increased by twofold in stop-flow samples derived from the proximal tubule, indicating net secretion during stopped flow. The stop-flow pattern of MTX excretion was similar, except the base-line flow pattern of MTX excretion was similar, except the base-line (U/P)MTX/(U/P)In ratio exceeded 1.0, indicating net secretion during both free-flow and stopped-flow periods. Secretion of both compounds was inhibited by p-aminohippuric acid and other organic acids but not by L-glutamic acid. It is concluded that folic acid is transported bidirectionally, while evidence was obtained only for secretion of MTX.

Effect of Na and impermeant anions on renal K transport during stopped flow

1961 ◽  
Vol 201 (5) ◽  
pp. 774-780 ◽  
Author(s):  
Lawrence P. Sullivan
Keyword(s):  
Renal Artery ◽  
Maximum Concentration ◽  
Flow Patterns ◽  
Stopped Flow ◽  
K Transport ◽  
Stop Flow ◽  
Concentration Patterns

The influence of increased urinary concentrations of NaCl and Na2SO4 upon the stop flow concentration patterns for potassium has been studied. Hypertonic NaCl and Na2SO4 solutions were infused into the renal artery of dogs before and during a period of stopped flow. The NaCl infusions increased the maximum concentration of potassium achieved during stopped flow but had no effect on the minimum concentrations reached. Na2SO4 infusions shifted the locus of the maximum concentrations of potassium to a more proximal location in the stop flow patterns whereas NaCl infusions did not. It is concluded that the minimum concentrations of potassium in the stop flow patterns are the result of increased reabsorption rather than decreased secretion due to a lack of sodium. The alteration in the pattern produced by Na2SO4 is due to the presence of the impermeant anion rather than increased sodium concentrations.

Calsequestrin is essential for the Ca2+ release induced by myotoxin α in skeletal muscle sarcoplasmic reticulum

1995 ◽  
Vol 73 (8) ◽  
pp. 1181-1185 ◽  
Author(s):  
Masamichi Ohkura ◽  
Ken-Ichi Furukawa ◽  
Yasushi Ohizumi ◽  
Tory Ide ◽  
Takashi Kawasaki ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Channel Blocker ◽  
Single Channel ◽  
Heavy Fraction ◽  
Stopped Flow ◽  
Single Channel Recording ◽  
Excitatory Effect ◽  
Crotalus Viridis ◽  
Channel Currents ◽  
Flow Experiments

Myotoxin α (MYTX), a polypeptide toxin purified from the venom of prairie rattlesnakes (Crotalus viridis viridis), induced Ca2+ release from the heavy fraction of skeletal sarcoplasmic reticulum (HSR), using a Ca2+ electrode. The effect of MYTX was nearly abolished by pretreatment with ryanodine, an alkaloid-based Ca2+ channel blocker. In the stopped-flow experiments, MYTX increased the choline+ permeability of HSR in the presence of calsequestrin (CS). Single channel recording experiments showed that in the presence of CS, the channel currents were markedly enhanced by MYTX applied to the cis side, but not to the trans side. However, in the absence of CS, MYTX failed to cause the excitatory effect in both the experiments. These results suggest that CS is essential for MYTX-induced Ca2+ release through the Ca2+ release channels in skeletal HSR.Key words: calsequestrin, myotoxin α, Ca2+ release, Ca2+ release channels, sarcoplasmic reticulum.

TRANSPORT OF ALDOSTERONE AND OF THE ACID LABILE CONJUGATE OF ALDOSTERONE BY TUBULAR CELLS OF THE KIDNEY

1967 ◽  
Vol 55 (4) ◽  
pp. 648-655 ◽  
Author(s):  
K. A. Deck ◽  
W. E. Siegenthaler
Keyword(s):  
Urine Samples ◽  
Tubular Cells ◽  
Proximal Tubular ◽  
Flow Experiments ◽  
Stop Flow ◽  
Acid Labile

ABSTRACT Stop flow experiments on dogs receiving continuous infusions of radioactive aldosterone were carried out in order to determine the tubular sites of reabsorption of aldosterone and the tubular sites of secretion of its metabolites. Sodium, p-aminohippuric acid, creatinine, inulin, radioactive aldosterone, radioactive tetrahydroaldosterone and the acid-labile (hydrolyzable) conjugate of aldosterone were analyzed in the urine samples collected after the stop periods. The results of the experiments indicate that aldosterone is mainly reabsorbed at a distal tubular site, that the acid-labile conjugate is secreted mainly at a proximal tubular site, and that tetrahydroaldosterone glucuronide is neither secreted nor reabsorbed by tubular cells. Predominant distal reabsorption of aldosterone is suggested as being a possible reason for the predominant distal sodium-retaining effect of this hormone.

Impaired diluting capacity of the thick ascending limb during loop bicarbonate and nitrate perfusion in vivo

1984 ◽  
Vol 62 (11) ◽  
pp. 1416-1422 ◽  
Author(s):  
Hans-Ulrich Gutsche ◽  
Linda N. Peterson ◽  
Karl-Heinz Sauerwald ◽  
David Z. Levine
Keyword(s):  
Animal Studies ◽  
Urine Concentration ◽  
Thick Ascending Limb ◽  
Distal Nephron ◽  
Nacl Transport ◽  
Minimum Concentration ◽  
Bicarbonate Solutions ◽  
Flow Experiments ◽  
Stop Flow

Previous whole animal studies have indicated that when nitrate or bicarbonate is substituted for chloride, renal concentrating defects can be demonstrated. It has been proposed that function of the "distal nephron" or thick ascending limb may be impaired when chloride is replaced by other anions. To examine this proposal, microstop-flow experiments were performed in rats in which loops were perfused with solutions containing 110 mM NaCl, NaHCO3, or NaNO3. Solute reabsorption by the thick ascending limb was assessed by measuring the minimum conductivity of fluid emerging from the loop following intervals of stop-flow. Thick ascending limb solute transport was impaired in loops perfused with HCO3 or NO3 evidenced by the marked increase in solute remaining in the loop after 60 s of stop-flow. The calculated corresponding sodium concentrations were in the range of 17–24 mM Na for the NaCl perfusion, 57–88 mM Na for the NaHCO3 perfusion, and 57–69 mM Na for the NaNO3 perfusion. Clearly, the minimum concentration achieved with NaCl was approximately one-third of that reached with the nitrate or bicarbonate solutions. These results indicate that when chloride-poor solutions reach the thick ascending limb, an important impairment of diluting capacity is demonstrable in vivo in the rat. The present studies, therefore, provide an important link between recent information regarding the mechanism of NaCl transport in the thick ascending limb and older whole animal studies suggesting an important role for distal chloride delivery in urine concentration.

Use of Viscogens, dNTPαS, and Rhodium(III) as Probes in Stopped-Flow Experiments To Obtain New Evidence for the Mechanism of Catalysis by DNA Polymerase β†,‡

Biochemistry ◽  
2005 ◽  
Vol 44 (13) ◽  
pp. 5177-5187 ◽  
Author(s):  
Marina Bakhtina ◽  
Soojin Lee ◽  
Yu Wang ◽  
Chris Dunlap ◽  
Brandon Lamarche ◽  
...  
Keyword(s):  
Dna Polymerase ◽  
Stopped Flow ◽  
Dna Polymerase Β ◽  
Mechanism Of Catalysis ◽  
New Evidence ◽  
Flow Experiments

The dependence of the rates of reduction of cobalt(III)-μ-peroxo complexes on isomeric structure

1984 ◽  
Vol 62 (11) ◽  
pp. 2127-2130 ◽  
Author(s):  
Steve C. F. Au-Yeung ◽  
Donald R. Eaton
Keyword(s):  
Rate Constants ◽  
Chemical Shifts ◽  
Cobalt Complex ◽  
Stopped Flow ◽  
Ferrous Ions ◽  
Point Charge Model ◽  
Isomeric Structure ◽  
Initial Reduction ◽  
Charge Model ◽  
Flow Experiments

The reaction of μ-peroxybis(ethylenediamine)bis(diethylenetriamine)cobalt(III) with ferrous ions has been studied by stopped flow spectrophotometry and by 59Co nmr. Two separate initial reduction steps with second order rate constants of 1.07 and 3.04 M−1 s−1, respectively, can be discerned in the stopped flow experiments. These two rate constants are assigned to inner sphere reduction of the aef,cd,b and edf,ac,b isomers of the peroxy cobalt complex, respectively. The different isomers can be distinguished by 59Co nmr. If there is insufficient Fe2+ present to completely reduce the complex to Co(II) and water, the change in the relative intensities of the 59Co resonances after partial reduction shows that one isomer has reacted faster than the other. The 59Co resonances can be assigned to the different isomers on the basis of a point charge model for the chemical shifts and line widths. Based on this model it is concluded that the isomer with the central NH of the diethylenetriamine trans to the peroxy ligand reacts faster. This result is compared to literature reports on the relative rates of substitution of isomers of Co(III) complexes with ethylenediamine and diethylenetriamine ligands.

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