User:Acosaj1/sandbox

Selected Article: Tubuloglomerular feedback

I want to add more background information. I want to further explain the importance of the system and expand the information provided on glomerular filtration rate and purinergic signaling. I think I can also improve the article by adding more information in the modulation section regarding the different factors that may modulate the sensitivity of tubuloglomerular feedback.

Plan:

I want to add more background information and add info regarding glomerular filtration and purinergic signaling. I think I can also improve the article by adding more information in the modulation section regarding the different factors that may modulate the sensitivity of tubuloglomerular feedback. I hope to incorporate information from reliable sources.

Possible sources I plan to use:

1. Layton, A. T., & Edwards, A. (2014). Tubuloglomerular Feedback. Mathematical Modeling In Renal Physiology, 85. doi:10.1007/978-3-642-27367-4_5

2. Thurau, K., & Takabatake, T. (1991). Tubuloglomerular feedback system.

3. Wang, H., D'Ambrosio, M. A., Ren, Y., Monu, S. R., Leung, P., Kutskill, K., & ... Carretero, O. A. (2015). Tubuloglomerular and connecting tubuloglomerular feedback during inhibition of various Na transporters in the nephron. American Journal Of Physiology (Consolidated), (5), 1026. doi:10.1152/ajprenal.00605.2014

4. Ren, Y., D'Ambrosio, M., Garvin, J., Wang, H., & Carretero, O. (2013). Mechanism of inhibition of tubuloglomerular feedback by CO and cGMP. Hypertension, doi:10.1161/HYPERTENSIONAHA.113.01164

5. Song, J., Lu, Y., Wei, J., Wang, L., Wang, S., Shen, C., & ... Lai, E. (2014). Oxidative status in the macula densa modulates tubuloglomerular feedback responsiveness in Angiotensin II-induced hypertension. Acta Physiologica, doi:10.1111/apha.12358 — 

Widmaier, Eric P., Hershel Raff, Kevin T. Strang, and Arthur J. Vander.  Vander's Human Physiology: The Mechanisms of Body Function. 14th ed. New York: McGraw-Hill, 2016. Print

found more sources WEEK 6:

6. Ryu, H., & Layton, A. (2014). Tubular fluid flow and distal NaCl delivery mediated by tubuloglomerular feedback in the rat kidney. Journal Of Mathematical Biology, 68(4), 1023. doi:10.1007/s00285-013-0667-5

7. '''''Schnermann, J. (2015). Concurrent Activation of Multiple Vasoactive Signaling Pathways in Vasoconstriction Caused by Tubuloglomerular Feedback: A Quantitative Assessment. Annual Review Of Physiology, 77301. doi:10.1146/annurev-physiol-021014-071829'''''

WEEK 9:

8. Wang, T., Kawabata, M., Haneda, M., & Takabatake, T. (2003). Effects of uroguanylin, an intestinal natriuretic peptide, on tubuloglomerular feedback. Hypertension Research, 26(7), 577-582. doi:10.1291/hypres.26.577

https://www.jstage.jst.go.jp/article/hypres/26/7/26_7_577/_pdf

WEEK 10:

9. Renal interstitial pressure and tubuloglomerular feedback control in rats during infusion of atrial natriuretic peptide (ANP). (1992). Acta Physiologica Scandinavica, (3), 393.

http://onlinelibrary.wiley.com/doi/10.1111/j.1748-1716.1992.tb09434.x/pdf

10. YiLin, R., Janic, B., Kutskill, K., Peterson, E. L., & Carretero, O. A. (2016). Mechanisms of connecting tubule glomerular feedback enhancement by aldosterone. American Journal Of Physiology: Renal Physiology, 311(6), F1182. doi:10.1152/ajprenal.00076.2016

http://ajprenal.physiology.org.avoserv2.library.fordham.edu/content/311/6/F1182.full

11. Ren, Y., D'Ambrosio, M., Garvin, J., Wang, H., & Carretero, O. (2013). Mechanism of inhibition of tubuloglomerular feedback by CO and cGMP. Hypertension, doi:10.1161/HYPERTENSIONAHA.113.01164

http://eds.a.ebscohost.com.avoserv2.library.fordham.edu/eds/detail/detail?vid=2&sid=9b78ac15-7942-4e30-8c8f-73b43ae8d084%40sessionmgr4007&hid=4111&bdata=JnNpdGU9ZWRzLWxpdmU%3d#AN=edselc.2-52.0-84877041912&db=edselc

12. Liu, Z. )., Schmerbach, K. )., Perlewitz, A. )., Nikitina, T. )., Cantow, K. )., Seeliger, E. )., & ... Liu, R. ). (2014). Iodinated contrast media cause direct tubular cell damage, leading to oxidative stress, low nitric oxide, and impairment of tubuloglomerular feedback. American Journal Of Physiology - Renal Physiology, 306(8), F864-F872. doi:10.1152/ajprenal.00302.2013

http://ajprenal.physiology.org.avoserv2.library.fordham.edu/content/306/8/F864.full

SENEY JR., F. D., PERSSON, A. G., & WRIGHT, F. S. (1987). Modification of tubuloglomerular feedback signal by dietary protein. American Journal Of Physiology: Renal, Fluid & Electrolyte Physiology, 21(1), F83. (High protein-possible source)

Draft: Tubuloglomerular feedback

CHANGES ARE IN BOLD ITALICS

In the physiology of the kidney, tubuloglomerular feedback (TGF) is a feedback system inside the kidneys. Tubuloglomerular feedback is one of several mechanisms the kidney uses to regulate glomerular filtration rate (GFR). Within each nephron, information from the renal tubules (a downstream area of the tubular fluid) is signaled to the glomerulus (an upstream area). It involves the concept of purinergic signaling, in which an increased distal tubular sodium chloride concentration causes a basolateral release of adenosine from the macula densa cells. This initiates a cascade of events that ultimately brings GFR to an appropriate level.(1)(2)(3)

TGF maintains the extracellular fluid volume by preserving the balance between the glomerular filtration and tubular reabsorption rate. Any change in NaCl delivery to the macula densa induces a inverse change in tubular flow, thereby preventing acute fluctuations of flow and NaCl delivery in the distal nephron. Consequently, TGF limits urinary volume and sodium excretion, thereby helping maintain salt and water balance. 

== Content == 

• 1Background
• 2Mechanism
• 3Modulation
  • 3.1High-protein diet
• 4See also
• 5References

Background

Normal renal function requires that the flow through the nephron is kept within a narrow range. When tubular flow (that is, GFR) lies outside this range, the ability of the nephron to maintain solute and water balance is compromised. Additionally, changes in GFR may result from changes in renal blood flow (RBF), which itself must be maintained within narrow limits. Elevated RBF may damage the glomerulus, while diminished RBF may deprive the kidney of oxygen. Tubuloglomerular feedback provides a mechanism by which changes in GFR can be detected and rapidly corrected for on a minute-to-minute basis as well as over sustained periods.

Regulation of GFR requires both a mechanism of detecting an inappropriate GFR as well as an effector mechanism that corrects it. The macula densa serves as the detector, while the glomerulus acts as the effector. When the macula densa detects an elevated GFR, it releases several molecules that cause the glomerulus to rapidly decrease its filtration rate. (Technically, the macula densa detects a SNGFR, single nephron GFR, but GFR is used here for simplicity.)

the article does not provide sources for the above information, I found the imfornation to come directly from the source I found (Ryu, H., & Layton, A. (2014). Tubular fluid flow and distal NaCl delivery mediated by tubuloglomerular feedback in the rat kidney. Journal Of Mathematical Biology, 68(4), 1023. doi:10.1007/s00285-013-0667-5)

ADD/EDIT:

The kidney maintains the electrolyte concentrations, osmolality, and acid-base balance of blood plasma within the narrow limits that are compatible with effective cellular function; and the kidney participates in blood pressure regulation and in the maintenance of steady whole-organism water volume 

Fluid flow through the nephron must be kept within a narrow range for normal renal function in order to not compromise the ability of the nephron to maintain salt and water balance. Tubuloglomerular feedback (TGF) regulates tubular flow by detecting and correcting changes in GFR. Active transepithelial transport is used by the thick ascending limb (TAL) cells to pump NaCl to the surrounding interstitium from luminal fluid. The Tubular fluid is diluted because the cell's walls are water-impermeable and do not lose water as NaCl is actively reabsorbed. Thus, the TAL is an important segment of the TGF system, and its transport properties allow it to act as a key operator of the TGF system. A reduction of GFR occurs as a result of TGF when NaCl concentration at the sensor site is increased within the physiological range of approximately 10 to 60 mM. 

The TGF mechanism is a negative feedback loop in which the chloride ion concentration is sensed downstream in the nephron by the macula densa (MD), cells in the tubular wall near the end of TAL and the glomerulus. The muscle tension in the afferent arteriole is modified based on the difference between the sensed concentration and a target concentration. Vasodilation of the afferent arteriole, which results in increased glomerular filtration pressure and tubular fluid flow, occurs when MD cells detect a chloride concentration that is below a target value. A higher fluid flow rate in the TAL allows less time for dilution of the tubular fluid so that MD chloride concentration increases. Glomerular flow is decreased if the chloride concentration is above the target value. Constricting the smooth muscle cells in the afferent arteriole, results in a reduced concentration of chloride at the MD. TGF can stabilizes the fluid and solute delivery into the distal portion of the loop of Henle and maintain the rate of filtration near its ideal value using these mechanisms.

Mechanism

The macula densa is a collection of densely packed epithelial cells at the junction of the thick ascending limb (TAL) and distal convoluted tubule (DCT). As the TAL ascends through the renal cortex, it encounters its own glomerulus, bringing the macula densa to rest at the angle between the afferent and efferent arterioles. The macula densa's position enables it to rapidly alter glomerular resistance in response to changes in the flow rate through the distal nephron.

The macula densa uses the composition of the tubular fluid as an indicator of GFR. A large sodium chloride concentration is indicative of an elevated GFR, while low sodium chloride concentration indicates a depressed GFR. Sodium chloride is sensed by the macula densa mainly by an apical Na-K-2Cl cotransporter (NKCC2). The relationship between the TGF and NKCC2 can be seen through the administration of loop diuretics like furosemide. Furosemide blocks NaCl reabsorption mediated by the NKCC2 at the macula densa, which leads to increased renin release. Excluding loop diuretic use, the usual situation that causes a reduction in reabsorption of NaCl via the NKCC2 at the macula densa is a low tubular lumen concentration of NaCl. Reduced NaCl uptake via the NKCC2 at the macula densa leads to increased renin release, which leads to restoration of plasma volume, and to dilation of the afferent arterioles, which leads to increased renal plasma flow and increased GFR.

The macula densa's detection of elevated sodium chloride concentration in the tubular lumen, which leads to a decrease in GFR, is based on the concept of purinergic signaling.

In response to increased flow of tubular fluid in the thick ascending limb/ increased sodium chloride (salt) concentration at the macula densa:

1. Elevated filtration at the glomerulus or reduced reabsorption of sodium and water by the Proximal Convoluted Tubule causes the tubular fluid at the macula densa to have a higher concentration of sodium chloride.
2. Apical Na-K-2Cl cotransporters (NKCC2), which are found on the surface of the macula densa cells, are exposed to the fluid with a higher sodium concentration, and as a result more sodium is transported into the cells.
3. The macula densa cells do not have enough Na/K ATPases on their basolateral surface to excrete this added sodium. This results in an increase of the cell's osmolarity.
4. Water flows into the cell along the osmotic gradient, causing the cell to swell. When the cell swells, ATP escapes though a basolateral, stretch-activated, non-selective Maxi-Anion channel. The ATP is subsequently converted to adenosine by ecto-5′-nucleotidase.
5. Adenosine constricts the afferent arteriole by binding with high affinity to the A₁ receptors a G_i/G_o, not to be confused with the α₁ receptor, which utilizes the G_q. Adenosine binds with much lower affinity to A_2A and A_2B receptors causing dilation of efferent arterioles.
6. The binding of adenosine to the A₁ receptor causes a complex signal cascade involving the G_i subunit deactivating Ac, thus reducing cAMP and the G_o subunit activating PLC, IP3 and DAG. The IP3 causes the release of intracellular calcium, which spreads to neighboring cells via gap junctions creating a "TGF calcium wave". This causes afferent arteriolar vasoconstriction, decreasing the glomerular filtrate rate.
7. The G_i and increased intracellular calcium, cause a decrease in cAMP which inhibits Renin release from the juxtaglomerular cells. In addition, when macula densa cells detect higher concentrations of Na and Cl, they inhibit nitric oxide synthetase (decreasing renin release), but the most important inhibitory mechanism of renin synthesis and release is elevations in juxtaglomerular cell calcium concentration.

In response to decreased flow of tubular fluid in the thick ascending limb / decreased salt concentration at the macula densa:

1. Reduced filtration at the glomerulus or increased reabsorption of sodium and water by the Proximal Convoluted Tubule causes fluid in the tubule at the macula densa to have a reduced concentration of sodium chloride (because there was more time for sodium chloride to be reabsorbed from that fluid in the thick ascending limb).
2. NKCC2 has a lower activity and subsequently causes a complicated signaling cascade involving the activation of: p38, (ERK½), (MAP) kinases, (COX-2) and microsomal prostaglandin E synthase (mPGES) in the macula densa.
3. This causes the synthesis and release of PGE2.
4. PGE2 acts on EP2 and EP4 receptors in juxtaglomerular cells and causes renin release.
5. Renin release activates RAAS leading to many outcomes including an increased GFR.

The mechanism section does not have sources. (yes on original)

Missing info about juxtaglomerular apparatus (JGA) that regulate GFR by tubuloglomerular feedback (TGF)

" The critical target of the trans-JGA signaling cascade is the glomerular afferent arteriole; its response consists of an increase in net vasoconstrictor tone resulting in reductions of glomerular capillary pressure (PGC) and glomerular plasma flow. Efferent arterioles appear to play a lesser role; experimental evidence supports both vasoconstriction and vasodilation, with perhaps the former in the lower range and the latter in the higher range of NaCl concentrations (2). When feedback regulation of afferent arteriolar tone is prevented by interrupting the feedback loop, and when the sensing mechanism is fully activated by saturating NaCl concentrations, TGF reduces GFR on average by approximately 45% and PGC by approximately 20%. Afferent arteriolar resistance increases by 50% or less, consistent with a radius reduction of approximately 10%, if Poiseuille's law holds. Thus, TGF-induced vasoconstriction is usually limited in magnitude; " (SCHNERMANN)

Modulation

There are several factors that may modulate the sensitivity of tubuloglomerular feedback. A decreased sensitivity results in higher tubular perfusion, while an increased sensitivity results in lower tubular perfusion. NO source provided

ADD: A mediating agent is released or generated as a function of changes in luminal NaCl concentration. The size of the TGF response is directly dependent upon these changes. "In part because of the striking effect of deletion of A1 adenosine receptors (A1AR), adenosine generated from released ATP has been proposed as the critical TGF mediator. "(Schnermann mentions this and I will try to find more info and edit the sentence)

 A modulating agent affects the TGF response without input regarding luminal NaCl. The agents are vasoactive substances that alter either the magnitude or the sensitivity of the TGF response. (ADD CITE: Schnermann)

Factors that decrease TGF sensitivity include:

The macula densa plaque consists of a group of spe- cialized epithelial cells located in the distal segment of the thick ascending limb of the nephron which serve as "luminal sensors of sodium chloride (NaCl) concentration. An increase in the NaCl delivery to the macula densa promotes release of adenosine and/or ATP, leading to afferent arteriolar constriction and decrease in the single nephron glomerular filtration" 

• atrial natriuretic peptide
  • I will try to get access to this article: http://onlinelibrary.wiley.com/doi/10.1111/j.1748-1716.1992.tb09434.x/pdf
• nitric oxide

The oxidative stress in the macula dense is determined by interactions between nitric oxide (NO) and superoxide (O ). TGF response is normally controlled by the NO generated in the macula dense. in Ang II induced hypertension, the TGF response is mainly controlled by the O 2 generated by the macula dense." (ADD CITE: SONG)

• cAMP
• PGI₂
• high-protein diet
  • The threshold at which the loop of Henle flow rate initiates feedback responses is affected. A high preteen diet affects the feedback activity by making the single nephron glomerular filtration rate higher, and the Na and Cl concentrations in early distal tubule fluid lower. The signal eliciting the TG feedback response is affected. The increased load on the kidney of high-protein diet is a result of an increase in reabsorption of NaCl.
  • The increased load on the kidney of high-protein diet is a result of an increase in reabsorption of NaCl. This causes a decrease in the sensitivity of tubuloglomerular feedback, which, in turn, results in an increased glomerular filtration rate. This increases pressure in glomerular capillaries. When added to any additional renal disease, this may cause permanent glomerular damage. NO SOURCE PROVIDED

ADD WHAT IS BELOW FROM HIGH PROTEIN DIET

Factors that increase TGF sensitivity include:

• adenosine
• thromboxane
• 5-HETE
• angiotensin II
• prostaglandin E2
• aldosterone
  • Aldosterone within the connecting tubule lumen enhances connecting tubule glomerular feedback (CTGF) via a nongenomic effect involving GPR30 receptors and sodium/hydrogen exchanger (NHE). Aldosterone inside the connecting tubule lumen enhances CTGF via a cAMP/PKA/PKC pathway and stimulates O2− generation and this process may contribute to renal damage by increasing glomerular capillary pressure.

High-protein diet[edit | edit source]

The increased load on the kidney of high-protein diet is a result of an increase in reabsorption of NaCl. This causes a decrease in the sensitivity of tubuloglomerular feedback, which, in turn, results in an increased glomerular filtration rate. This increases pressure in glomerular capillaries. When added to any additional renal disease, this may cause permanent glomerular damage. NO SOURCE PROVIDED

See also

• Myogenic Mechanism
• Kidney
• Juxtaglomerular Apparatus
• Renal corpuscle

References

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4. ^ Jump up to: ^a b c d 
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7. ^ Jump up to: ^a b 
8. Jump up ^ W S Spielman, L J Arend, "Adenosine receptors and signaling in the kidney.", American Heart Association, 1991
9. ^ Jump up to: ^a b 
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11. ^ Jump up to: ^a b 
12. ^ Jump up to: ^a b c Walter F., PhD. Boron (2005). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3.