Insulin Increases Sodium (Na+) Channel Density in A6 Epithelia: Implications for Expression of Hypertension

1999 ◽  
Vol 1 (1) ◽  
pp. 20-29 ◽  
Author(s):  
Lynn M. Baxendale-Cox ◽  
Randall L. Duncan
Keyword(s):  
Cell Model ◽  
Single Gene ◽  
Distal Tubule ◽  
High Plasma ◽  
Primary Hypertension ◽  
Na Channel ◽  
Electrolyte Balance ◽  
Multifactorial Disease ◽  
Channel Density ◽  
Intermediate Phenotypes

Essential or primary hypertension is a multifactorial disease that is expressed as a result of complex interactions between genes and environmental influences. Several mutations in many different proteins are associated with expression of hypertension, including abnormalities in the epithelial sodium channel (ENaC) found in absorptive organs (i.e., distal colon, distal tubule of the nephron). Some of these mutations result in structural and/or functional alterations in ENaC-mediated Na+ entry in epithelia responsible for fluid and electrolyte balance and are associated with expression of hypertension. Studies support the notion that there is a link between ENaC and hypertension of both the monogenic (single gene mutation) and primary or essential type (a multifactorial disease). Alterations of other aspects of the environment of absorptive cells (e.g., hyperinsulinemia, hyperaldosteronemia, high plasma cortisol, high plasma Na+) have also been shown to elicit hyperabsorption of Na+ via ENaC and therefore could contribute significantly to expression of hypertension in people with intermediate phenotypes. This article describes an initial study in which the effects of an environmental factor, extracellular levels of insulin, on ENaC were examined in a normal kidney cell model. Electrophysiologic techniques revealed that ENaC density rapidly increased in response to addition of insulin to the basolateral bath. This autoregulatory recruitment of Na+ total channel density masked a slight decrease in open channel probability. Insulin’s effect on ENaC function and implications on fluid and electrolyte balance and expression of primary hypertension is discussed.

scholarly journals Direct observation of frequency modulated transcription in single cells using light activation

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Daniel R Larson ◽  
Christoph Fritzsch ◽  
Liang Sun ◽  
Xiuhau Meng ◽  
David S Lawrence ◽  
...  
Keyword(s):  
Single Cell ◽  
Single Molecule ◽  
Single Cell Analysis ◽  
Cell Model ◽  
Single Cells ◽  
Single Gene ◽  
Gene Activation ◽  
Light Activation ◽  
Dynamic Synthesis ◽  
Single Cell Model

Single-cell analysis has revealed that transcription is dynamic and stochastic, but tools are lacking that can determine the mechanism operating at a single gene. Here we utilize single-molecule observations of RNA in fixed and living cells to develop a single-cell model of steroid-receptor mediated gene activation. We determine that steroids drive mRNA synthesis by frequency modulation of transcription. This digital behavior in single cells gives rise to the well-known analog dose response across the population. To test this model, we developed a light-activation technology to turn on a single steroid-responsive gene and follow dynamic synthesis of RNA from the activated locus.

Complex cardiovascular diseases: the genetics of arterial hypertension

ESC CardioMed ◽  
2018 ◽  
pp. 732-736
Author(s):  
Georg Ehret
Keyword(s):  
Blood Pressure ◽  
Arterial Hypertension ◽  
Genetic Variants ◽  
Single Gene ◽  
Primary Hypertension ◽  
Genetic Types ◽  
Risk Variants ◽  
Cardiovascular Risk Prediction ◽  
Single Gene Defect ◽  
Substantial Extent

Arterial hypertension appears as two genetic types: primary hypertension is to a substantial extent determined by a large number of genetic risk variants, whereas rare patients with a familial hypertensive syndrome have a single gene defect that drives the elevated blood pressure. The familial hypertensive syndromes have been instrumental in highlighting blood pressure-regulating pathways that almost exclusively cluster in the kidney and in the mineralocorticoid pathways. Conversely, hundreds or more genetic variants cause the genetic component of primary hypertension and each risk variant causes a small blood pressure increase. The blood vessels appear to be one tissue in which these variants principally act and surprisingly there is little overlap with pathways of kidney and hormone pathways. Genetic testing is useful for the rare familial hypertensive syndrome, but in primary hypertension cardiovascular risk prediction can currently not be improved by genotyping.

Mechanism of acidification along cortical distal tubule of the rat

1994 ◽  
Vol 266 (2) ◽  
pp. F218-F226 ◽  
Author(s):  
R. Fernandez ◽  
M. J. Lopes ◽  
R. F. de Lira ◽  
W. F. Dantas ◽  
E. J. Cragoe Junior ◽  
...  
Keyword(s):  
Channel Blocker ◽  
Exchange Resin ◽  
Rat Kidney ◽  
Specific Inhibitor ◽  
Distal Tubule ◽  
Ringer Solution ◽  
Na Channel ◽  
Bafilomycin A1 ◽  
Bicarbonate Reabsorption ◽  
Distal Tubules

The cellular mechanism of luminal acidification (bicarbonate reabsorption) was studied in cortical distal tubules of rat kidney. The stopped-flow microperfusion technique was applied to early distal (ED) and late distal (LD) segments, perfused with bicarbonate Ringer solution to which specific inhibitors were added, to measure bicarbonate reabsorption [HCO3 flux (JHCO3)]. pH and transepithelial potential difference (Vt) were recorded by double-barreled H+ exchange resin/reference (1 M KCl) electrodes. Amiloride increased stationary pH and reduced Vt in both early and late segments. Hexamethylene-amiloride (HMA), a specific Na(+)-H+ exchange blocker, reduced JHCO3 in both segments (ED by 43.6 and LD by 40.3%) without affecting Vt. Benzamil, an Na(+)-channel blocker, reduced Vt by 75.9 in ED and 74.9% in LD but had no significant effect on acidification in both segments. The specific inhibitor of H(+)-ATPase, bafilomycin A1, inhibited LD JHCO3 at a concentration of 2 x 10(-7) M by 49%, but ED was inhibited by 24% only at 2 x 10(-6) M. Sch-28080, an inhibitor of gastric H(+)-K(+)-ATPase, reduced JHCO3 by 35% in LD of K(+)-depleted rats but not in control rats and had no effect on ED. These data indicate that, in ED, bicarbonate reabsorption is mediated mostly by Na(+)-H+ exchange. In LD, there is evidence for contribution of Na(+)-H+ exchange, vacuolar H(+)-ATPase, and H(+)-K(+)-ATPase (in K(+)-depleted rats) to bicarbonate reabsorption.

Epithelial Na channels and short-term renal response to salt deprivation

2002 ◽  
Vol 283 (4) ◽  
pp. F717-F726 ◽  
Author(s):  
Gustavo Frindt ◽  
Tiffany McNair ◽  
Anke Dahlmann ◽  
Emily Jacobs-Palmer ◽  
Lawrence G. Palmer
Keyword(s):  
Distal Tubule ◽  
Treated Group ◽  
Na Channel ◽  
Na Channels ◽  
Nacl Transport ◽  
Drug Concentrations ◽  
Epithelial Na Channels ◽  
Late Evening ◽  
Excretion Rates

To test the role of epithelial Na channels in the day-to-day regulation of renal Na excretion, rats were infused via osmotic minipumps with the Na channel blocker amiloride at rates that achieved drug concentrations of 2–5 μM in the lumen of the distal nephron. Daily Na excretion rates were unchanged, although amiloride-treated animals tended to excrete more Na in the afternoon and less in the late evening than controls. When the rats were given a low-Na diet, Na excretion rates were elevated in the amiloride-treated group within 4 h and remained higher than controls for at least 48 h. Adrenalectomized animals responded similarly to the low-Na diet. In contrast, rats infused with polythiazide at rates designed to inhibit NaCl transport in the distal tubule were able to conserve Na as well as did the controls. Injection of aldosterone (2 μg/100 g body wt) decreased Na excretion in control animals after a 1-h delay. This effect was largely abolished in amiloride-treated rats. On the basis of quantitative analysis of the results, we conclude that activation of amiloride-sensitive channels by mineralocorticoids accounts for 50–80% of the immediate natriuretic response of the kidney to a reduction in Na intake. Furthermore, the channels are necessary to achieve minimal rates of Na excretion during more chronic Na deprivation.

Quantification of K+ secretion through apical low-conductance K channels in the CCD

2005 ◽  
Vol 289 (1) ◽  
pp. F117-F126 ◽  
Author(s):  
Daniel A. Gray ◽  
Gustavo Frindt ◽  
Lawrence G. Palmer
Keyword(s):  
Single Channel ◽  
Collecting Duct ◽  
Reversal Potential ◽  
Inward Rectification ◽  
Na Channel ◽  
Sk Channels ◽  
Maximal Conductance ◽  
Channel Density ◽  
Sk Channel ◽  
High K

Outward and inward currents through single small-conductance K+ (SK) channels were measured in cell-attached patches of the apical membrane of principal cells of the rat cortical collecting duct (CCD). Currents showed mild inward rectification with high [K+] in the pipette (Kp+), which decreased as Kp+ was lowered. Inward conductances had a hyperbolic dependence on Kp+ with half-maximal conductance at ∼20 mM. Outward conductances, measured near the reversal potential, also increased with Kp+ from 15 pS (Kp+ = 0) to 50 pS (Kp+ = 134 mM). SK channel density was measured as the number of conducting channels per patch in cell-attached patches. As reported previously, channel density increased when animals were on a high-K diet for 7 days. Addition of 8-cpt-cAMP to the bath at least 5 min before making a seal increased SK channel density to an even greater extent, although this increase was not additive with the effect of a high-K diet. In contrast, increases in Na channel activity, assessed as the whole cell amiloride-sensitive current, due to K loading and 8-cpt-cAMP treatment were additive. Single-channel conductances and channel densities were used as inputs to a simple mathematical model of the CCD to predict rates of transepithelial Na+ and K+ transport as a function of apical Na+ permeability and K+ conductance, basolateral pump rates and K+ conductance, and the paracellular conductance. With measured values for these parameters, the model predicted transport rates that were in good agreement with values measured in isolated, perfused tubules. The number and properties of SK channels account for K+ transport by the CCD under all physiological conditions tested.

scholarly journals Regulation of the sodium iodide symporter by iodide in FRTL-5 cells

2001 ◽  
pp. 139-144 ◽  
Author(s):  
PH Eng ◽  
GR Cardona ◽  
MC Previti ◽  
WW Chin ◽  
LE Braverman
Keyword(s):  
Sodium Iodide ◽  
Cell Model ◽  
High Plasma ◽  
Northern Analysis ◽  
Thyroid Cell ◽  
Transcriptional Level ◽  
Sodium Iodide Symporter ◽  
Iodide Transport ◽  
Excess Iodide

OBJECTIVE: The acute decrease in iodide organification in the thyroid in response to excess iodide is termed the acute Wolff-Chaikoff effect and normal organification resumes in spite of continued high plasma iodide concentrations (escape from the acute Wolff-Chaikoff effect). We have recently reported that large doses of iodide given to rats chronically decrease the sodium/iodide symporter (NIS) mRNA and protein, suggesting that escape is due to a decrease in NIS and subsequent iodide transport. We have now studied the effect of excess iodide on NIS in FRTL-5 cells to further explore the mechanisms whereby excess iodide decreases NIS. DESIGN: FRTL-5 cells were employed and were incubated in the presence or absence of various concentrations of iodide. NIS mRNA and protein and the turnover of NIS were assessed. METHODS: NIS mRNA was measured by Northern analysis, NIS protein by Western analysis and NIS turnover by pulse-chase labeling experiments. RESULTS: Iodide (10(-) mol/l) had no effect on NIS mRNA in FRTL-5 cells at 24 and 48 h compared with cells cultured in the absence of iodide. However, excess iodide decreased NIS protein by 50% of control values at 24 h and by 70% at 48 h. This effect of iodide was dose dependent. Pulse-chase experiments demonstrated that there was no effect of iodide on new NIS protein synthesis and that the turnover of NIS protein in the presence of iodide was 27% faster than in the absence of added iodide. CONCLUSIONS: Excess iodide does not decrease NIS mRNA in FRTL-5 cells but does decrease NIS protein, suggesting that in this in vitro thyroid cell model iodide modulates NIS, at least in part, at a post-transcriptional level. This iodide-induced decrease in NIS protein appears to be due, at least partially, to an increase in NIS protein turnover.

Relationship between energy expenditure and ion channel density in the turtle and rat brain

1989 ◽  
Vol 257 (6) ◽  
pp. R1354-R1358 ◽  
Author(s):  
R. A. Edwards ◽  
P. L. Lutz ◽  
D. G. Baden
Keyword(s):  
Energy Consumption ◽  
Energy Expenditure ◽  
Ion Channel ◽  
Rat Brain ◽  
Receptor Interaction ◽  
Na Channel ◽  
Apparent Difference ◽  
Na Channels ◽  
Channel Density ◽  
Rat Synaptosomes

Synaptosomes were isolated from turtle and rat brains to determine whether differences in brain ion channel densities accounted for the turtle's ability to survive anoxia compared with the mammal. The Na(+)-channel binding neurotoxin brevetoxin showed high-affinity specific binding in both turtle and rat synaptosomes, suggesting specific ligand-receptor interaction. The maximum binding capacity (Bmax) value for the turtle was only about one-third of that found for the rat synaptosomes, suggesting that the turtle synaptosome has a correspondingly lower Na+ channel density than the rat. This apparent difference in Na+ channel density is not reflected in metabolic rates, since at the same temperature (31 degrees C) the O2 consumption of both the rat and turtle synaptosome was almost identical. The large reductions in energy expenditure seen in synaptosomes incubated in Na(+)-free media and in media containing ouabain (approximately 50% turtle, 80% rat) are probably related to the halting of transmembrane Na(+)-K+ exchange. The greater reduction in the rat may be related to the apparent greater density of Na+ channels in the rat brain. However, compared with the 90% reduction in brain metabolism that occurs when the turtle brain becomes anoxic, the differences in ion channel density and in the costs of ion pumping between the rat and turtle brain are trivial. Closing Na+ channels with tetrodotoxin and increasing Na+ channel activation with veratridine caused substantial decreases and increases in synaptosome energy consumption, respectively. This suggests that the modulation of ion channel conductance has a significant effect on metabolic cost and may be an important mechanism to reduce energy consumption and electrical activity in the anoxic turtle brain, while still maintaining ionic gradients.

Electrophysiology and noise analysis of K+-depolarized epithelia of frog skin

1985 ◽  
Vol 249 (5) ◽  
pp. C421-C429 ◽  
Author(s):  
J. Tang ◽  
F. J. Abramcheck ◽  
W. Van Driessche ◽  
S. I. Helman
Keyword(s):  
Frog Skin ◽  
Single Channel ◽  
Apical Membrane ◽  
Short Circuit ◽  
Noise Analysis ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Membrane Resistance ◽  
Na Channel ◽  
Channel Density

Epithelia of frog skin bathed either symmetrically with a sulfate-Ringer solution or bathed asymmetrically and depolarized with a 112 mM K+ basolateral solution (Kb+) were studied with intracellular microelectrode techniques. Kb+ depolarization caused an initial decrease of the short-circuit current (Isc) with a subsequent return of the Isc toward control values in 60-90 min. Whereas basolateral membrane resistance (Rb) and voltage were decreased markedly by high [Kb+], apical membrane electrical resistance (Ra) was decreased also. After 60 min, intracellular voltage averaged -27.3 mV, transcellular fractional resistance (fRa) was 86.8%, and Ra and Rb were decreased to 36.1 and 13.0%, of their control values, respectively. Amiloride-induced noise analysis of the apical membrane Na+ channels revealed that Na+ channel density was increased approximately 72% while single-channel Na+ current was decreased to 39.9% of control, roughly proportional to the decrease of apical membrane voltage (34.0% of control). In control and Kb+-depolarized epithelia, the Na+ channel density exhibited a phenomenon of autoregulation. Inhibition of Na+ entry (by amiloride) caused large increases of Na+ channel density toward saturating values of approximately 520 X 10(6) channels/cm2 in Kb+-depolarized tissues.

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