Faculty Opinions recommendation of Crosstalk between the connecting tubule and the afferent arteriole regulates renal microcirculation.

In obesity, renal damage is caused by increase in renal blood flow (RBF), glomerular capillary pressure (P GC ), and single nephron glomerular filtration rate but the mechanism behind this alteration in renal hemodynamics is unclear. P GC is controlled mainly by the afferent arteriole (Af-Art) resistance. Af-Art resistance is regulated by mechanism similar to that in other arterioles and in addition, it is regulated by two intrinsic feedback mechanisms: 1) tubuloglomerular feedback (TGF) that causes Af-Art constriction in response to an increase in sodium chloride (NaCl) in the macula densa, via sodium–potassium-2-chloride cotransporter-2 (NKCC2) and 2) connecting tubule glomerular feedback (CTGF) that causes Af-Art dilatation and is mediated by connecting tubule via epithelial sodium channel (ENaC). CTGF is blocked by the ENaC inhibitor benzamil. Attenuation of TGF reduces Af-Art resistance and allows systemic pressure to get transmitted to the glomerulus that causes glomerular barotrauma/damage. In the current study, we tested the hypothesis that TGF is attenuated in obesity and that CTGF contributes to this effect. We used Zucker obese rats (ZOR) while Zucker lean rats (ZLR) served as controls. We performed in-vivo renal micropuncture of individual rat nephrons while measuring stop-flow pressure (P SF ), an index of P GC. TGF response was measured as a decrease in P SF induced by changing the rate of late proximal perfusion from 0 to 40nl/min in stepwise manner.CTGF was calculated as the difference of P SF value between vehicle and benzamil treatment, at each perfusion rate. Maximal TGF response was significantly less in ZOR (6.16 ± 0.52 mmHg) when compared to the ZLR (8.35 ± 1.00mmHg), p<0.05 , indicating TGF resetting in the ZOR. CTGF was significantly higher in ZOR (6.33±1.95 mmHg) when compared to ZLR (1.38±0.89 mmHg), p<0.05 . When CTGF was inhibited with the ENaC blocker Benzamil (1μM), maximum P SF decrease was 12.30±1.72 mmHg in ZOR and 10.60 ± 1.73 mmHg in ZLR, indicating that blockade of CTGF restored TGF response in ZOR. These observations led us to conclude that TGF is reset in ZOR and that enhanced CTGF contributes to this effect. Increase in CTGF may explain higher renal blood flow, increased P GC and higher glomerular damage in obesity.

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Abstract P325: Enhanced Afferent Arteriole Dilatation in Dahl Salt-sensitive Rats (dahlss): Role of Connecting Tubule Glomerular Feedback (ctgf)

Hypertension ◽

10.1161/hyp.68.suppl_1.p325 ◽

2016 ◽

Vol 68 (suppl_1) ◽

Author(s):

Hong Wang ◽

Cesar A Romero ◽

Branislava Janic ◽

Edwards Peterson ◽

Oscar A Carretero

Keyword(s):

Indirect Measurement ◽

Tubuloglomerular Feedback ◽

Afferent Arteriole ◽

High Salt Diet ◽

Connecting Tubule ◽

Simultaneous Inhibition ◽

Flow Pressure ◽

Tubular Flow

Afferent arteriole (Af-Art) resistance is modulated by 2 intrinsic nephron feedbacks: the vasoconstrictor tubuloglomerular feedback (TGF) and the vasodilator CTGF. TGF is mediated by NKCC2 channel in the macula densa and blocked by furosemide; and CTGF is mediated by ENaC in the connecting tubule and blocked by benzamil. Previously we measured CTGF indirectly, by differences between TGF response with and without CTGF blocker benzamil. Thus, using this indirect measurement we reported that Dahl SS have greater CTGF than Dahl salt-resistant rats (Dahl SR). We have recently developed a new method to measure CTGF more directly and we found that when we simultaneously blocked TGF with furosemide and CTGF with benzamil, the increasing tubular perfusion caused Af-Art constriction (TGF-like) that is mediated by the NHE. W e hypothesize that in vivo during simultaneous inhibition of NKCC2 and the NHE, CTGF causes an Af-Art dilatation revealed by an increase in stop-flow pressure (P SF ) and that is greater in Dahl SS than in Dahl SR in a high salt diet. In the presence of furosemide alone, increasing nephron perfusion did not change the P SF in neither Dahl SS nor Dahl SR. When we blocked both, NKCC2 with furosemide and NHE with DMA, increase in tubular flow caused Af-Art dilation that was demonstrated by an increase in P SF . This increase was greater in Dahl SS (5.1±0.4 mmHg) than in Dahl SR (2.9±0.3 mmHg; P < 0.01), (Fig).We confirm that CTGF causes this vasodilation, since benzamil completely blocked this effect. We conclude that during inhibition of NKCC2 and NHE in the nephron CTGF (Af-Art dilatation) is enhanced in Dahl SS as compared to Dahl SR.

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Connecting tubule glomerular feedback antagonizes tubuloglomerular feedback in vivo

AJP Renal Physiology ◽

10.1152/ajprenal.00403.2010 ◽

2010 ◽

Vol 299 (6) ◽

pp. F1374-F1378 ◽

Cited By ~ 21

Author(s):

H. Wang ◽

J. L. Garvin ◽

M. A. D'Ambrosio ◽

Y. Ren ◽

O. A. Carretero

Keyword(s):

Tubuloglomerular Feedback ◽

Afferent Arteriole ◽

In Vitro Experiments ◽

Nacl Transport ◽

Connecting Tubule ◽

Vasoconstrictor Effect ◽

Flow Pressure ◽

Stop Flow

In vitro experiments showed that the connecting tubule (CNT) sends a signal that dilates the afferent arteriole (Af-Art) when Na+ reabsorption in the CNT lumen increases. We call this process CNT glomerular feedback (CTGF) to differentiate it from tubuloglomerular feedback (TGF), which is a cross talk between the macula densa (MD) and the Af-Art. In TGF, the MD signals the Af-Art to constrict when NaCl transport by the MD is enhanced by increased luminal NaCl. CTGF is mediated by CNT Na+ transport via epithelial Na+ channels (ENaC). However, we do not know whether CTGF occurs in vivo or whether it opposes the increase in Af-Art resistance caused by TGF. We hypothesized that CTGF occurs in vivo and opposes TGF. To test our hypothesis, we conducted in vivo micropuncture of individual rat nephrons, measuring stop-flow pressure (PSF) as an index of glomerular filtration pressure. To test whether activation of CTGF opposes TGF, we used benzamil to block CNT Na+ transport and thus CTGF. CTGF inhibition with the ENaC blocker benzamil (1 μM) potentiated the decrease in PSF at 40 and 80 nl/min. Next, we tested whether we could augment CTGF by inhibiting NaCl reabsorption in the distal convoluted tubule with hydrochlorothiazide (HCTZ, 1 mM) to enhance NaCl delivery to the CNT. In the presence of HCTZ, benzamil potentiated the decrease in PSF at 20, 40, and 80 nl/min. We concluded that in vivo CTGF occurs and opposes the vasoconstrictor effect of TGF.

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A Novel Mechanism of Renal Microcirculation Regulation: Connecting Tubule-Glomerular Feedback

Current Hypertension Reports ◽

10.1007/s11906-019-0911-5 ◽

2019 ◽

Vol 21 (1) ◽

Cited By ~ 2

Author(s):

Cesar A. Romero ◽

Oscar A. Carretero

Keyword(s):

Connecting Tubule ◽

Renal Microcirculation

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Connecting tubule glomerular feedback mediates acute tubuloglomerular feedback resetting

AJP Renal Physiology ◽

10.1152/ajprenal.00673.2011 ◽

2012 ◽

Vol 302 (10) ◽

pp. F1300-F1304 ◽

Cited By ~ 16

Author(s):

Hong Wang ◽

Martin A. D'Ambrosio ◽

Jeffrey L. Garvin ◽

Yilin Ren ◽

Oscar A. Carretero

Keyword(s):

Carbonic Anhydrase ◽

Proximal Tubule ◽

Sodium Channels ◽

Tubuloglomerular Feedback ◽

Afferent Arteriole ◽

Epithelial Sodium Channels ◽

Connecting Tubule ◽

Before And After ◽

Flow Pressure ◽

Stop Flow

Tubuloglomerular feedback (TGF) and connecting tubule glomerular feedback (CTGF) are mechanisms that control afferent arteriole (Af-Art) tone. TGF, initiated by increased NaCl at the macula densa, causes Af-Art constriction. Prolonged activation of TGF leads to an attenuation or “resetting” of its constrictor effect. The mechanisms of TGF resetting remain incompletely understood. CTGF is initiated by increased NaCl in the connecting tubule and Na+ entry via epithelial sodium channels (ENaC). Contrary to TGF, CTGF dilates the Af-Art. Here, we hypothesize that CTGF, in part, mediates TGF resetting. We performed micropuncture of individual rat nephrons while measuring stop-flow pressure (PSF), an index of glomerular filtration pressure and Af-Art tone. Increases in Af-Art tone cause PSF to decrease. TGF responses, measured as the decrease in PSF induced by switching late proximal tubule perfusion from 5 to 40 nl/min, were elicited before and after a 30-min period of sustained perfusion of the late proximal tubule at a rate of 40 nl/min designed to induce TGF resetting. TGF responses were 7.3 ± 0.3 and 4.9 ± 0.2 mmHg before and after resetting was induced ( P < 0.001, n = 6). When CTGF was inhibited with the ENaC blocker benzamil (1 μM), TGF responses were 9.5 ± 0.3 and 8.8 ± 0.6 mmHg (NS, n = 6), thus resetting was abolished. In the presence of the carbonic anhydrase inhibitor acetazolamide (10 mM), TGF responses were 8.8 ± 0.6 and 3.3 ± 0.4 mmHg before and after resetting ( P < 0.001, n = 6). With both acetazolamide and benzamil, TGF responses were 10.4 ± 0.2 and 8.4 ± 0.5 mmHg ( P < 0.01, n = 6), thus resetting was attenuated. We conclude that CTGF, in part, mediates acutely induced TGF resetting.

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Abstract 552: Aldosterone Enhances Connecting Tubule Glomerular Feedback (CTGF)

Hypertension ◽

10.1161/hyp.62.suppl_1.a552 ◽

2013 ◽

Vol 62 (suppl_1) ◽

Author(s):

YiLin Ren ◽

Martin A D'Ambrosio ◽

Jeffrey L Garvin ◽

Pablo Leung ◽

Hong Wang ◽

...

Keyword(s):

Renal Damage ◽

Actinomycin D ◽

Maximal Response ◽

Mineralocorticoid Receptors ◽

Afferent Arteriole ◽

Connecting Tubule ◽

Left Shift ◽

Epithelial Na Channels ◽

Transcription Inhibitor ◽

Translation Inhibitor

Increasing Na delivery to the connecting tubule (CNT) stimulates epithelial Na channels (ENaC) and dilates the afferent arteriole (Af-Art), a process we call connecting tubule glomerular feedback (CTGF). We hypothesize that aldosterone (aldo) enhances CTGF via a nongenomic mechanism that stimulates CNT ENaC via GPR30 and/or mineralocorticoid receptors (MR). Rabbit Af-Arts and their adherent CNTs were microdissected and simultaneously perfused. Two consecutive CTGF curves were elicited by increasing luminal NaCl in the CNT. Addition of aldo 10 -8 M to the CNT potentiated CTGF, seen as a left-shift in the concentration of NaCl that elicited a half-maximal response (EC 50 ), see Figure. The MR blocker eplerenone (10 -5 M) prevented the enhancement of CTGF by aldo (control EC 50 = 32.4 ± 2.3 mM; aldo + eplerenone EC 50 = 35.4 ± 1.7 mM; n = 7). Neither the transcription inhibitor actinomycin D (5x10 -6 M) nor the translation inhibitor cycloheximide (10 -5 M) prevented the effect of aldo (control EC 50 = 33.0 ± 2.0 mM; aldo + actinomycin D EC 50 = 15.4 ± 1.5 mM; n = 6; P < 0.001, control EC 50 = 33.2 ± 2.4 mM; aldo + cycloheximide EC 50 = 11.2 ± 1.3 mM; n = 6; P < 0.001). We conclude that aldo in the lumen of the CNT enhances CTGF via a nongenomic effect possibly involving MR and/or GPR30 receptors. Enhanced CTGF induced by aldosterone may contribute to renal damage by causing increases in Af-Art dilation and glomerular capillary pressure (glomerular barotrauma). Figure. Control CTGF (○) seen as dilation of norepinephrine-preconstricted Af-Arts induced by increasing NaCl in the CNT. Aldo 10 -8 M (•) enhanced CTGF (n = 6; * P < 0.05; ** P < 0.01; *** P < 0.001; vs . control). Vertical dashed lines indicate EC 50 .

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Abstract 490: Constrictor Mechanism of the Afferent Arteriole Initiated by Na/H Exchanger in the Nephron

Hypertension ◽

10.1161/hyp.60.suppl_1.a490 ◽

2012 ◽

Vol 60 (suppl_1) ◽

Author(s):

Hong Wang ◽

Martin A D'Ambrosio ◽

YiLin Ren ◽

Jeffrey L Garvin ◽

Oscar A Carretero

Keyword(s):

Macula Densa ◽

Tubuloglomerular Feedback ◽

Na Channel ◽

Afferent Arteriole ◽

Renal Vasculature ◽

Connecting Tubule ◽

Flow Pressure ◽

Stop Flow ◽

Epithelial Na Channel

The afferent arteriole (Af-Art) accounts for most of renal vasculature resistance, thus controlling glomerular filtration rate and renal function. Two mechanisms have been described in which the nephron helps control Af-Art resistance, namely tubuloglomerular feedback (TGF), and connecting tubule glomerular feedback (CTGF). TGF is a constrictor mechanism initiated at the macula densa by the Na/K/2Cl cotransporter (NKCC2), while CTGF is a dilator mechanism initiated at the connecting tubule by the epithelial Na channel (ENaC). However, when NKCC2 is blocked by furosemide, CTGF-induced Af-Art dilation is not evident, thus we hypothesize that there is a constrictor mechanism that is furosemide-insensitive and counters CTGF. To test this, we used in vivo micropuncture of single nephrons. Stop-flow pressure (P SF ) was measured as an index of glomerular capillary pressure (which decreases when the Af-Art constricts). Two consecutive P SF curves were generated by raising nephron perfusion from 0 to 40 nL/min while adding drugs to the tubular perfusate. The decrease in P SF induced by increasing nephron perfusion was blocked by furosemide 10 -4 M (control: 7.9±0.2 mmHg, furosemide: 0.4±0.2 mmHg, P <0.001, n=6), but was partially restored when blocking CTGF with the ENaC inhibitor benzamil 10 -6 M (furosemide: 0.2±0.1 mmHg, furosemide+benzamil: 4.3±0.3 mmHg, P <0.001, n=6). A possible explanation for these observations is that TGF may be activated to some degree by Na/H exchanger (NHE)-mediated Na entry at the macula densa when NKCC2 is blocked. When we added the NHE blocker dimethylamiloride (DMA, 10 -4 M) in the presence of furosemide and benzamil, the decrease in PSF was significantly prevented (furosemide+benzamil: 4.6±0.3 mmHg, furosemide+benzamil+DMA: 1.1±0.2 mmHg, P <0.001, n=6). Therefore, we conclude that a constrictor mechanism of the Af-Art is initiated by NHE in the nephron and is observable when NKCC2-mediated TGF and ENaC-mediated CTGF have been blocked.

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Abstract P148: Connecting Tubule-glomerular Feedback (ctgf) in Renal Hemodynamics and Blood Pressure (bp) After Unilateral Nephrectomy (unx)

Hypertension ◽

10.1161/hyp.68.suppl_1.p148 ◽

2016 ◽

Vol 68 (suppl_1) ◽

Author(s):

Cesar A Romero ◽

Sumit Monu ◽

Robert Knight ◽

Oscar A Carretero

Keyword(s):

Blood Flow ◽

Renal Blood Flow ◽

Tubuloglomerular Feedback ◽

Unilateral Nephrectomy ◽

Afferent Arteriole ◽

Sprague Dawley ◽

High Sodium ◽

Connecting Tubule ◽

Chronic Infusion

Afferent arteriole resistance is regulated in part by myogenic response, tubuloglomerular feedback (TGF) and connecting tubule-glomerular feedback (CTGF). CTGF dilates afferent arteriole in response to high sodium in connecting tubule (CNT) counteracting and shifting to the right the TGF response (resetting); CTGF increases renal blood flow and glomerular pressure, both favoring glomerular filtration and sodium excretion. CTGF is initiated by epithelial sodium channel (ENaC) in CNT and inhibited by Benzamil. Unilateral nephrectomy (UNx) is accompanied by TGF resetting, increase in renal blood flow (RBF) and single nephron GFR in the remnant kidney, without any changes in systemic BP. We evaluated the effects of CTGF in TGF resetting, RBF and BP after UNx. UNx was performed on Sprague-Dawley rats and 24h later TGF was evaluated in vivo by renal micropuncture techniques by measure stop flow pressure (Psf). CTGF was evaluated by the differences between TGF maximal responses (TGFmax) with or without tubular benzamil perfusion. Another set of animals received chronic infusion of benzamil directly into the kidney, that started 1 week before UNx. Renal blood flow (RBF) was measured by arterial spin labeling-MRI 24h before and 24h after the UNx. Direct BP measurement was performed before and 3 weeks after the UNx. After UNx, TGF resetting was observed in UNx rats (TGFmax 8±1 vs. 1±1 mmHg, Sham vs. UNx; p<0.05). This TGF resetting was inhibited by benzamil. RBF increased after the UNx in comparison to sham and this increase was prevented by chronic infusion of Benzamil into the kidney (Sham: 3±0.6; UNx: 4.6±0.3; UNx+Benzamil 3.5±0.6 ml/min/g tissue p<0.002). Basal mean BP values were not different between the vehicle or treated rats before the UNx; however 3 weeks after the UNx, rats receiving benzamil into the kidney showed higher mean BP values than vehicle (88±0.3 vs. 97±4 mmHg, p<0.01). We conclude that CTGF participates in TGF resetting and RBF regulation after UNx, and that could participate in BP regulation after UNx.

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