scholarly journals Purinergic Receptor Signaling at the Basolateral Membrane of Macula Densa Cells

2002 ◽  
Vol 13 (5) ◽  
pp. 1145-1151 ◽  
Author(s):  
R. Liu
Keyword(s):  
Purinergic Receptor ◽  
Basolateral Membrane ◽  
Macula Densa ◽  
Receptor Signaling

scholarly journals Effects of NKCC2 isoform regulation on NaCl transport in thick ascending limb and macula densa: a modeling study

2014 ◽  
Vol 307 (2) ◽  
pp. F137-F146 ◽  
Author(s):  
Aurélie Edwards ◽  
Hayo Castrop ◽  
Kamel Laghmani ◽  
Volker Vallon ◽  
Anita T. Layton
Keyword(s):  
Cell Model ◽  
Basolateral Membrane ◽  
Macula Densa ◽  
Tubuloglomerular Feedback ◽  
Thick Ascending Limb ◽  
Differential Splicing ◽  
Dietary Salt ◽  
Nacl Transport ◽  
Low Salt

This study aims to understand the extent to which modulation of the Na+-K+-2Cl− cotransporter NKCC2 differential splicing affects NaCl delivery to the macula densa. NaCl absorption by the thick ascending limb and macula densa cells is mediated by apical NKCC2. A recent study has indicated that differential splicing of NKCC2 is modulated by dietary salt (Schieβl IM, Rosenauer A, Kattler V, Minuth WW, Oppermann M, Castrop H. Am J Physiol Renal Physiol 305: F1139–F1148, 2013). Given the markedly different ion affinities of its splice variants, modulation of NKCC2 differential splicing is believed to impact NaCl reabsorption. To assess the validity of that hypothesis, we have developed a mathematical model of macula densa cell transport and incorporated that cell model into a previously applied model of the thick ascending limb (Weinstein AM, Krahn TA. Am J Physiol Renal Physiol 298: F525–F542, 2010). The macula densa model predicts a 27.4- and 13.1-mV depolarization of the basolateral membrane [as a surrogate for activation of tubuloglomerular feedback (TGF)] when luminal NaCl concentration is increased from 25 to 145 mM or luminal K+ concentration is increased from 1.5 to 3.5 mM, respectively, consistent with experimental measurements. Simulations indicate that with luminal solute concentrations consistent with in vivo conditions near the macula densa, NKCC2 operates near its equilibrium state. Results also suggest that modulation of NKCC2 differential splicing by low salt, which induces a shift from NKCC2-A to NKCC2-B primarily in the cortical thick ascending limb and macula densa cells, significantly enhances salt reabsorption in the thick limb and reduces Na+ and Cl− delivery to the macula densa by 3.7 and 12.5%, respectively. Simulation results also predict that the NKCC2 isoform shift hyperpolarizes the macula densa basolateral cell membrane, which, taken in isolation, may inhibit the release of the TGF signal. However, excessive early distal salt delivery and renal salt loss during a low-salt diet may be prevented by an asymmetric TGF response, which may be more sensitive to flow increases.

scholarly journals The Mitochondrial Barriers Segregate Agonist-induced Calcium-dependent Functions in Human Airway Epithelia

2003 ◽  
Vol 122 (4) ◽  
pp. 377-387 ◽  
Author(s):  
Carla M. Pedrosa Ribeiro ◽  
Anthony M. Paradiso ◽  
Alessandra Livraghi ◽  
Richard C. Boucher
Keyword(s):  
Purinergic Receptor ◽  
Basolateral Membrane ◽  
Receptor Activation ◽  
Airway Epithelial ◽  
Airway Epithelia ◽  
Cl Secretion ◽  
Epithelial Monolayers ◽  
Human Airway ◽  
Human Airway Epithelia

In airway epithelia, purinergic receptor (P2Y2-R) stimulation of intracellular calcium (Ca2+i)–regulated ion transport is restricted to the membrane domain ipsilateral to receptor activation, implying compartmentalization of Ca2+i signaling. Because mitochondria can spatially restrict cellular Ca2+i signals, immunocytochemical, electron microscopic, and fluorescent studies of mitochondria localization were performed in human airway epithelia. Although concentrated at the apical domain, mitochondria were found distributed at both the apical and the basolateral poles and in close association with the endoplasmic reticulum. The role of mitochondria in locally restricting P2Y2-R–induced Ca2+i signals was investigated by measuring changes in mitochondrial Ca2+ (Ca2+m) in human airway epithelial monolayers. P2Y2-R activation induced Ca2+m accumulation in mitochondria confined to the domain ipsilateral to P2Y2-R stimulation, which was blocked by mitochondrial uncoupling with 1 μM CCCP and 2.5 μg/ml oligomycin. The role of mitochondria in restricting the cellular cross-talk between basolateral P2Y2-R–dependent Ca2+i mobilization and apical membrane Ca2+-activated Cl− secretion was investigated in studies simultaneously measuring Ca2+i and Cl− secretion in cystic fibrosis human airway epithelial monolayers. Activation of basolateral P2Y2-Rs produced similar increases in Ca2+i in monolayers without and with pretreatment with uncouplers, whereas Ca2+i-activated Cl− secretion was only efficiently triggered in mitochondria-uncoupled conditions. We conclude that (a) mitochondria function as a Ca2+i-buffering system in airway epithelia, compartmentalizing Ca2+i-dependent functions to the membrane ipsilateral to receptor stimulation; and (b) the mitochondria provide structural barriers that protect the airway epithelia against nonspecific activation of Ca2+i-modulated functions associated with Ca2+i signals emanating from the apical or the basolateral membrane domains.

Direct evidence for apical Na+:2Cl-:K+ cotransport in macula densa cells

1990 ◽  
Vol 258 (5) ◽  
pp. F1466-F1469 ◽  
Author(s):  
J. Y. Lapointe ◽  
P. D. Bell ◽  
J. Cardinal
Keyword(s):  
Direct Evidence ◽  
Basolateral Membrane ◽  
Macula Densa ◽  
Membrane Voltage ◽  
Nacl Transport ◽  
Nacl Concentration ◽  
Nacl Secretion ◽  
Microelectrode Techniques

Previous studies by our laboratory indicate that increases in apical NaCl concentration ([NaCl]) depolarize macula densa (MD) cells, although the mechanism for apical NaCl transport was not identified. To determine the pathway for MD apical NaCl transport, we utilized microdissected cortical thick ascending limbs (CTAL) with attached glomeruli and conventional microelectrode techniques. Addition of 50 microM furosemide in the presence of 150 mM NaCl produced a variable hyperpolarization of basolateral membrane voltage (delta Vbl, -14 +/- 8.2 mV, NS P = 0.15, n = 6) and completely blocked the expected repolarization on reducing luminal [NaCl] from 150 to 25 mM. Addition of furosemide in the presence of 25 mM NaCl depolarized Vbl by 22 +/- 6.8 mV (P less than 0.05, n = 6) indicating that the direction of the NaCl transport can be reversed in low luminal [NaCl]. In other studies, luminal concentration of Na or Cl was increased from 25 to 150 mM. Increased [Na] produced a 6.9 +/- 1.2 mV (n = 9) depolarization, whereas Cl addition depolarized Vbl by 8.2 +/- 1.7 mV (n = 5), suggesting that both ions are involved in the NaCl-induced MD depolarization. Removal of K from the luminal perfusate elicited a hyperpolarization of -14 +/- 2.9 mV (n = 9). These results are all consistent with the existence of an apical Na+:2Cl-:K+ transporter that would result in NaCl reabsorption in the presence of 150 mM luminal NaCl but would produce NaCl secretion at low luminal NaCl concentrations.

Direct measurement of basolateral membrane potentials from cells of the macula densa

1989 ◽  
Vol 257 (3) ◽  
pp. F463-F468 ◽  
Author(s):  
P. D. Bell ◽  
J. Y. Lapointe ◽  
J. Cardinal
Keyword(s):  
Membrane Potential ◽  
Direct Measurement ◽  
Basolateral Membrane ◽  
Membrane Potentials ◽  
Macula Densa ◽  
Rabbit Kidney ◽  
Fluid Composition ◽  
Nacl Solution ◽  
Basolateral Membrane Potential

At the present time, little is known concerning the electrophysiology of the cells of the macula densa and whether or not these cells are electrically responsive to alterations in luminal fluid composition. To investigate this issue, cortical thick ascending limbs (CTAL) containing macula densa and attached glomeruli were dissected from rabbit kidney and the CTAL perfused in vitro. Basolateral membrane potential (Vbl) was measured with microelectrodes in macula densa cells and, for comparison, in cells of the CTAL. Macula densa Vbl averaged -56.5 +/- 7.6 mV (n = 4) at a (n = 22) at 20 mM NaCl, -35.6 +/- 3.9 mV (n = 16) at 45 mM NaCl, and -25.5 +/- 2.6 mV (n = 32) at 150 mm NaCl. Thus macula densa Vbl depolarized markedly (31 mV) when luminal perfusate [NaCl] was increased from low to high values. In contrast, Vbl measured in CTAL cells averaged -62 +/- 6.1 mV (n = 6) in 45 mM NaCl and did not change significantly as perfusate NaCl was increased to 150 mM. In the presence of 150 mM NaCl, luminal application of furosemide (50 microM) produced a small (3.5 +/- 1.1 mV, n = 16) but statistically significant (P less than 0.02) hyperpolarization in macula densa cells, whereas CTAL cell Vbl hyperpolarized markedly (20 +/- 5.7 mV, n = 6) with addition of furosemide. Finally, neither macula densa cells nor the CTAL cells changed Vbl when 45 mM NaCl solution was made hypotonic by removing mannitol.(ABSTRACT TRUNCATED AT 250 WORDS)

Basolateral ionic permeabilities of macula densa cells

1991 ◽  
Vol 260 (6) ◽  
pp. F856-F860 ◽  
Author(s):  
J. Y. Lapointe ◽  
P. D. Bell ◽  
A. M. Hurst ◽  
J. Cardinal
Keyword(s):  
Membrane Potential ◽  
Basolateral Membrane ◽  
Ringer Solution ◽  
Macula Densa ◽  
Bathing Solution ◽  
Liquid Junction ◽  
Transport Pathways ◽  
Cl Conductance ◽  
Junction Potential ◽  
Basolateral Membrane Potential

It has recently been shown that membrane ionic transport pathways of macula densa cells can be measured using conventional microelectrodes. To determine if conductances could be identified at the basolateral membrane of macula densa cells, cortical thick ascending limbs (CTAL) with attached glomeruli were continuously perfused with a 25 mM NaCl bicarbonate-free Ringer solution. Individual basolateral Na+, Cl-, NaCl, and K+ concentrations were altered by isosmotic replacement with N-methyl-D-glucamine and/or cyclamate. Reduction in basolateral [Na+] from 150 to 25 mM hyperpolarized basolateral membrane potential (Vbl) by 9.9 +/- 1.3 mV (n = 10; all data are corrected for changes in liquid junction potential at bath electrode). A decrease in bath [Cl-] from 150 to 25 mM depolarized Vbl by 20 +/- 2.4 mV (n = 13), whereas decreases in bath [NaCl] from 150 to 25 mM depolarized Vbl by 29 +/- 6.8 mV (n = 5). In the presence of 150 mM NaCl bathing solution, a stepwise increase in [K+] from 5 to 15 mM (by replacement of 10 mM NaCl with 10 mM KCl) depolarized Vbl by 3.3 +/- 1.1 mV (n = 8). After correction for individual transepithelial diffusion potentials, Cl conductance averaged 59 +/- 19% of the total basolateral conductance, whereas K+ (23 +/- 8%) and Na+ (17 +/- 10%) contributed significantly less to the overall basolateral conductance. These results indicate that membrane potential of macula densa cells may be very sensitive to alterations in intracellular Cl- activity and suggest that apical transport of NaCl through a furosemide-sensitive Na(+)-K(+)-2Cl- transporter may affect membrane potential in macula densa cells via a change in intracellular Cl- activity.

Characterization of basolateral chloride/bicarbonate exchange in macula densa cells

2005 ◽  
Vol 288 (2) ◽  
pp. F380-F386 ◽  
Author(s):  
Peter Komlosi ◽  
Sebastian Frische ◽  
Amanda L. Fuson ◽  
Attila Fintha ◽  
Ákos Zsembery ◽  
...  
Keyword(s):  
Anion Exchange ◽  
Basolateral Membrane ◽  
Macula Densa ◽  
Rabbit Kidney ◽  
Thick Ascending Limb ◽  
Nacl Concentration ◽  
High Concentrations ◽  
Immunohistochemical Studies ◽  
Exchange Activity

Functional and immunohistological studies were performed to identify basolateral chloride/bicarbonate exchange in macula densa cells. Using the isolated, perfused thick ascending limb with attached glomerulus preparation dissected from rabbit kidney, macula densa intracellular pH (pHi) was measured with fluorescence microscopy and BCECF. For these experiments, basolateral chloride was reduced, resulting in reversible macula densa cell alkalinization. Anion exchange activity was assessed by measuring the maximal net base efflux on readdition of bath chloride. Anion exchange activity required the presence of bicarbonate, was independent of changes in membrane potential, did not require the presence of sodium, and was inhibited by high concentrations of DIDS. Inhibition of macula densa anion exchange activity by basolateral DIDS increased luminal NaCl concentration-induced elevations in pHi. Immunohistochemical studies using antibodies against AE2 demonstrated expression of AE2 along the basolateral membrane of macula densa cells of rabbit kidney. These results suggest that macula densa cells functionally and immunologically express a chloride/bicarbonate exchanger at the basolateral membrane. This transporter likely participates in the regulation of pHi and might be involved in macula densa signaling.

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