scholarly journals Action of Protein Tyrosine Kinase Inhibitors on the Hypotonicity-Stimulated Trafficking Kinetics of Epithelial Na+ Channels (ENaC) in Renal Epithelial Cells: Analysis Using a Mathematical Model

2018 ◽  
Vol 50 (1) ◽  
pp. 363-377 ◽  
Author(s):  
Rie Marunaka ◽  
Akiyuki Taruno ◽  
Toshiro Yamamoto ◽  
Narisato Kanamura ◽  
Yoshinori Marunaka
Keyword(s):  
Mathematical Model ◽  
Epithelial Cells ◽  
Intracellular Trafficking ◽  
Degradation Rate ◽  
Apical Membrane ◽  
Recycling Rate ◽  
Na Channels ◽  
Protein Tyrosine ◽  
Epithelial Na Channels ◽  
Hypotonic Condition

Background/Aims: Epithelial Na+ channels (ENaCs) play crucial roles in control of blood pressure by determining the total amount of renal Na+ reabsorption, which is regulated by various factors such as aldosterone, vasopressin, insulin and osmolality. The intracellular trafficking process of ENaCs regulates the amount of the ENaC-mediated Na+ reabsorption in the collecting duct of the kidney mainly by determining the number of ENaC expressed at the apical membrane of epithelial cells. Although we previously reported protein tyrosine kinases (PTKs) contributed to the ENaC-mediated epithelial Na+ reabsorption, we have no information on the role of PTKs in the intracellular ENaC trafficking. Methods: Using the mathematical model recently established in our laboratory, we studied the effect of PTKs inhibitors (PTKIs), AG1296 (10 µM: an inhibitor of the PDGF receptor (PDGFR)) and AG1478 (10 µM: an inhibitor of the EGF receptor (EGFR)) on the rates of the intracellular ENaC trafficking in renal epithelial A6 cells endogenously expressing ENaCs. Results: We found that application of PTKIs significantly reduced the insertion rate of ENaC to the apical membrane by 56%, the recycling rate of ENaC by 83%, the cumulative time of an individual ENaC staying in the apical membrane by 27%, the whole life-time after the first insertion of ENaC by 47%, and the cumulative Na+ absorption by 61%, while the degradation rate was increased to 3.8-fold by application of PTKIs. These observations indicate that PTKs contribute to the processes of insertion, recycling and degradation of ENaC in the intracellular trafficking process under a hypotonic condition. Conclusion: The present study indicates that application of EGFR and PDGFR-inhibitable PTKIs reduced the insertion rate (kI), and the recycling rate (kR) of ENaCs, but increased degradation rate (kD) in renal A6 epithelial cells under a hypotonic condition. These observations indicate that hypotonicity increases the surface expression of ENaCs by increasing the insertion rate (kI) and the recycling rate (kR) of ENaCs associated with a decrease in the degradation rate but without any significant effects on the endocytotic rate (kE) in EGFR and PDGFR-related PTKs-mediated pathways.

scholarly journals Analysis of Aprotinin, a Protease Inhibitor, Action on the Trafficking of Epithelial Na+ Channels (ENaC) in Renal Epithelial Cells Using a Mathematical Model

2017 ◽  
Vol 41 (5) ◽  
pp. 1865-1880 ◽  
Author(s):  
Kouhei Sasamoto ◽  
Rie Marunaka ◽  
Naomi Niisato ◽  
Hongxin Sun ◽  
Akiyuki Taruno ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Epithelial Cells ◽  
Protease Inhibitor ◽  
Apical Membrane ◽  
Recycling Rate ◽  
Na Channels ◽  
Extracellular Loop ◽  
Na Transport ◽  
Renal Epithelial Cells ◽  
Epithelial Na Channels

Background/Aim: Epithelial Na+ channels (ENaC) play a crucial role in control of blood pressure by regulating renal Na+ reabsorption. Intracellular trafficking of ENaC is one of the key regulators of ENaC function, but a quantitative description of intracellular recycling of endogenously expressed ENaC is unavailable. We attempt here to provide a model for intracellular recycling after applying a protease inhibitor under hypotonic conditions. Methods: We simulated the ENaC-mediated Na+ transport in renal epithelial A6 cells measured as short-circuit currents using a four-state mathematical ENaC trafficking model. Results: We developed a four-state mathematical model of ENaC trafficking in the cytosol of renal epithelial cells that consists of: an insertion state of ENaC that can be trafficked to the apical membrane state (insertion rate); an apical membrane state of ENaC conducting Na+ across the apical membrane; a recycling state containing ENaC that are retrieved from the apical membrane state (endocytotic rate) and then to the insertion state (recycling rate) communicating with the apical membrane state or to a degradation state (degradation rate). We studied the effect of aprotinin (a protease inhibitor) blocking protease-induced cleavage of the extracellular loop of γ ENaC subunit on the rates of intracellular ENaC trafficking using the above-defined four-state mathematical model of ENaC trafficking and the recycling number relative to ENaC staying in the apical membrane. We found that aprotinin significantly reduced the insertion rate of ENaC to the apical membrane by 40%, the recycling rate of ENaC by 81%, the cumulative time of an individual ENaC staying in the apical membrane by 32%, the cumulative life-time after the first endocytosis of ENaC by 25%, and the cumulative Na+ absorption by 31%. The most interesting result of the present study is that cleavage of ENaC affects the intracellular ENaC trafficking rate and determines the residency time of ENaC, indicating that more active cleaved ENaCs stay longer at the apical membrane contributing to transcellular Na+ transport via an increase in recycling of ENaC to the apical membrane. Conclusion: The extracellular protease-induced cleavage of the extracellular loop of γ ENaC subunit increases transcellular epithelial Na+ transport by elevating the recycling rate of ENaC due to an increase in the recycling rate of ENaCs associated with increases in the insertion rate of ENaC.

Cl-channel activation is necessary for stimulation of Na transport in adult alveolar epithelial cells

2000 ◽  
Vol 278 (2) ◽  
pp. L239-L244 ◽  
Author(s):  
Scott M. O'Grady ◽  
Xinpo Jiang ◽  
David H. Ingbar
Keyword(s):  
Epithelial Cells ◽  
Adrenergic Receptor ◽  
Apical Membrane ◽  
Receptor Activation ◽  
Alveolar Epithelial Cells ◽  
Na Channels ◽  
Channel Activation ◽  
Alveolar Epithelial ◽  
Cl Channel ◽  
Stimulation Of

In this review, we discuss evidence that supports the hypothesis that adrenergic stimulation of transepithelial Na absorption across the alveolar epithelium occurs indirectly by activation of apical Cl channels, resulting in hyperpolarization and an increased driving force for Na uptake through amiloride-sensitive Na channels. This hypothesis differs from the prevailing idea that adrenergic-receptor activation increases the open probability of Na channels, leading to an increase in apical membrane Na permeability and an increase in Na and fluid uptake from the alveolar space. We review results from cultured alveolar epithelial cell monolayer experiments that show increases in apical membrane Cl conductance in the absence of any change in Na conductance after stimulation by selective β-adrenergic-receptor agonists. We also discuss possible reasons for differences in Na-channel regulation in cells grown in monolayer culture compared with that in dissociated alveolar epithelial cells. Finally, we describe some preliminary in vivo data that suggest a role for Cl-channel activation in the process of amiloride-sensitive alveolar fluid absorption.

Effects of vasopressin and aldosterone on the lateral mobility of epithelial Na+ channels in A6 renal epithelial cells

1995 ◽  
Vol 147 (2) ◽  
Author(s):  
P.R. Smith ◽  
L.C. Stoner ◽  
S.C. Viggiano ◽  
K.J. Angelides ◽  
D.J. Benos
Keyword(s):  
Epithelial Cells ◽  
Na Channels ◽  
Lateral Mobility ◽  
Renal Epithelial Cells ◽  
Epithelial Na Channels

scholarly journals Gating of Na channels in the rat cortical collecting tubule: effects of voltage and membrane stretch.

1996 ◽  
Vol 107 (1) ◽  
pp. 35-45 ◽  
Author(s):  
L G Palmer ◽  
G Frindt
Keyword(s):  
Voltage Dependence ◽  
Single Channel ◽  
Apical Membrane ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Open Time ◽  
Collecting Tubule ◽  
Excised Patches ◽  
The Mean ◽  
Cortical Collecting Tubule

The gating kinetics of apical membrane Na channels in the rat cortical collecting tubule were assessed in cell-attached and inside-out excised patches from split-open tubules using the patch-clamp technique. In patches containing a single channel the open probability (Po) was variable, ranging from 0.05 to 0.9. The average Po was 0.5. However, the individual values were not distributed normally, but were mainly < or = 0.25 or > or = 0.75. Mean open times and mean closed times were correlated directly and inversely, respectively, with Po. In patches where a sufficient number of events could be recorded, two time constants were required to describe the open-time and closed-time distributions. In most patches in which basal Po was < 0.3 the channels could be activated by hyperpolarization of the apical membrane. In five such patches containing a single channel hyperpolarization by 40 mV increased Po by 10-fold, from 0.055 +/- 0.023 to 0.58 +/- 0.07. This change reflected an increase in the mean open time of the channels from 52 +/- 17 to 494 +/- 175 ms and a decrease in the mean closed time from 1,940 +/- 350 to 336 +/- 100 ms. These responses, however, could not be described by a simple voltage dependence of the opening and closing rates. In many cases significant delays in both the activation by hyperpolarization and deactivation by depolarization were observed. These delays ranged from several seconds to several tens of seconds. Similar effects of voltage were seen in cell-attached and excised patches, arguing against a voltage-dependent chemical modification of the channel, such as a phosphorylation. Rather, the channels appeared to switch between gating modes. These switches could be spontaneous but were strongly influenced by changes in membrane voltage. Voltage dependence of channel gating was also observed under whole-cell clamp conditions. To see if mechanical perturbations could also influence channel kinetics or gating mode, negative pressures of 10-60 mm Hg were applied to the patch pipette. In most cases (15 out of 22), this maneuver had no significant effect on channel behavior. In 6 out of 22 patches, however, there was a rapid and reversible increase in Po when the pressure was applied. In one patch, there was a reversible decrease. While no consistent effects of pressure could be documented, membrane deformation could contribute to the variation in Po under some conditions.

Epithelial Na Channels: Function and Diversity

1992 ◽  
Vol 54 (1) ◽  
pp. 51-66 ◽  
Author(s):  
L G Palmer
Keyword(s):  
Na Channels ◽  
Epithelial Na Channels

Different sodium chloride cotransport systems in the apical membrane of rabbit gallbladder epithelial cells

1983 ◽  
Vol 73 (3) ◽  
pp. 227-235 ◽  
Author(s):  
Dario Cremaschi ◽  
Giuliano Meyer ◽  
Sandra Bermano ◽  
Maurizia Marcati
Keyword(s):  
Sodium Chloride ◽  
Epithelial Cells ◽  
Apical Membrane ◽  
Rabbit Gallbladder ◽  
Cotransport Systems
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