Stimulation of chloride transport by cAMP in rat proximal tubules

1995 ◽  
Vol 268 (2) ◽  
pp. F204-F210 ◽  
Author(s):  
T. Wang ◽  
A. S. Segal ◽  
G. Giebisch ◽  
P. S. Aronson
Keyword(s):  
Proximal Tubule ◽  
Fluid Transport ◽  
Channel Blocker ◽  
Chloride Transport ◽  
Basolateral Membrane ◽  
Dibutyryl Camp ◽  
Cl Channel ◽  
Luminal Membrane ◽  
Cl Channels ◽  
Rat Proximal Tubule

We have previously demonstrated that formate and oxalate stimulate transcellular Cl- absorption (JCl) in the rat proximal tubule by a mechanism involving DIDS-sensitive anion exchange across the luminal membrane and diphenylamine-2-carboxylate (DPC)-sensitive Cl- channels in the basolateral membrane. Recent evidence indicates cAMP activation of Cl- channels in apical and basolateral membranes of proximal tubule cells. We therefore tested the effect of cAMP on Cl- and fluid transport in rat proximal tubule studied by luminal and capillary microperfusion in situ. The luminal perfusate contained 5 mM HCO3- and 145 mM Cl-, and the capillary perfusate contained 25 mM HCO3- and 110 mM Cl-, simulating conditions in the late proximal tubule. Addition of 0.5 mM dibutyryl cAMP markedly stimulated fluid absorption (Jv) and JCl. Similar effects resulted from addition of forskolin (10 microM) to stimulate cAMP production. The increments in Jv and JCl due to dibutyryl cAMP were abolished when the Cl- channel blocker DPC (200 microM) was added to the capillary perfusate but not when it was added to the lumen. The increments in Jv and JCl due to dibutyryl cAMP were unaffected by luminal DIDS (100 microM), which abolishes the increments in Jv and JCl induced by addition of oxalate. In contrast, the increments in Jv and JCl due to dibutyryl cAMP were abolished by luminal 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB; 10 microM), another Cl- channel blocker. Luminal NPPB had no effect on baseline Jv and JCl nor on the increments in Jv and JCl induced by addition of oxalate.(ABSTRACT TRUNCATED AT 250 WORDS)

Chloride transport in a mathematical model of the rat proximal tubule

1992 ◽  
Vol 263 (5) ◽  
pp. F784-F798 ◽  
Author(s):  
A. M. Weinstein
Keyword(s):  
Proximal Tubule ◽  
Chloride Transport ◽  
Basolateral Membrane ◽  
Model Calculations ◽  
Cl Transport ◽  
Luminal Membrane ◽  
Glomerular Filtrate ◽  
Thermodynamic Driving Force ◽  
Cytosolic Acidification ◽  
Rat Proximal Tubule

The proximal tubule model of this laboratory [Am. J. Physiol. 250 (Renal Fluid Electrolyte Physiol. 19): F860-F873, 1986] has been updated to examine proposed pathways for Cl- transport. Two additional buffer pairs have been added, i.e., HCO2-/H2CO2 and NH3/NH4+. At the luminal cell membrane Cl-/HCO2- and Cl-/HCO3- exchange are considered as pathways for Cl- entry, whereas at the peritubular membrane, Cl- exit occurs by either Na(+)-2HCO3-/Cl- exchange or K(+)-Cl- cotransport. Calculations with this model indicate that absolute proximal reabsorption of both Na+ and Cl- are critically dependent on the rate of luminal Na+/H+ exchange. In contrast, increases in the coefficient for Cl-/HCO2- exchange have little impact on overall Cl- flux, but, by enhancing base secretion, limit the depression of end-proximal HCO3-. Model calculations confirm those of Preisig and Alpern (J. Clin. Invest. 83: 1859–1867, 1989) showing that their measured value of luminal membrane H2CO2 permeability is inadequate to sustain the transcellular Cl- flux as Cl-/HCO2- exchange. Conversely, with sufficiently high H2CO2 permeability, luminal Cl- uptake is enhanced along the tubule, as HCO2- secretion and luminal acidification increase luminal H2CO2 to values severalfold greater than in glomerular filtrate. At the basolateral membrane, the thermodynamic driving force across the Na(+)-2HCO3-/Cl- exchanger is small. Although its contribution to steady-state Cl- exit may be less than the K(+)-Cl- cotransporter, the Na(+)-2HCO3-/Cl- exchanger can be a mechanism by which cytosolic acidification enhances peritubular Cl- transport, when luminal acidification enhances luminal Cl- uptake. A simulation is presented in which impermeant replacement of luminal Na+ leads to enhanced convective Cl- flux across the tight junction and alkalinization of the lateral interspace. In this setting, cytosolic Cl- depletion via the Na(+)-2HCO3-/Cl- exchanger may mimic luminal membrane Na(+)-Cl- cotransport.

Apical membrane Cl- channels in airway epithelia: anion selectivity and effect of an inhibitor

1990 ◽  
Vol 259 (2) ◽  
pp. C295-C301 ◽  
Author(s):  
M. Li ◽  
J. D. McCann ◽  
M. J. Welsh
Keyword(s):  
Channel Blocker ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Transepithelial Transport ◽  
Airway Epithelia ◽  
Cl Secretion ◽  
Cl Channel ◽  
Anion Selectivity ◽  
Cl Channels ◽  
Excised Patches

Previous work has investigated the anion selectivity of transepithelial Cl- secretion by airway epithelia and its inhibition by the Cl(-)-channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB). Here we report the anion selectivity of the apical membrane and of the outwardly rectifying Cl- channel and the effect of NPPB on the Cl- channel. The anion selectivity sequence of the apical membrane determined with conventional microelectrodes in the native epithelium was SCN- greater than I- greater than Br- greater than NO3- approximately Cl- much greater than SO(4)2- approximately gluconate-. This contrasts with the observation that Cl- and Br- support transepithelial secretion but that I- does not. Thus the anion selectivity of transepithelial transport is determined by the basolateral membrane Cl- entry step. The anion selectivity of the outwardly rectifying Cl- channel studied in excised patches was the same as that of the apical membrane. We also found that NPPB reversibly blocked the outwardly rectifying Cl- channel from both the internal and external surfaces of the patch. NPPB, 10 microM, completely blocked the channel; lower concentrations caused a decrease in the probability of finding the channel in the open state. NPPB also caused the appearance of a subconductance state of the channel, an occurrence which is rarely observed in the absence of NPPB. These data provide further support for the conclusion that the outwardly rectifying Cl- channel is responsible for Cl- exit from the cell across the apical membrane.

Mechanisms of chloride transport in the proximal tubule

1997 ◽  
Vol 273 (2) ◽  
pp. F179-F192 ◽  
Author(s):  
P. S. Aronson ◽  
G. Giebisch
Keyword(s):  
Steady State ◽  
Proximal Tubule ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Basolateral Membrane ◽  
Paracellular Transport ◽  
Additional Component ◽  
Major Fraction ◽  
Physiological Conditions ◽  
Cl Channels

The major fraction of filtered Cl- is reabsorbed in the proximal tubule. An important component of Cl- reabsorption is passive and paracellular, driven by the lumen-negative potential difference in the early proximal tubule and the outwardly directed concentration gradient for Cl- in the later proximal tubule. Evidence suggests that a significant additional component of NaCl reabsorption in the proximal tubule is active and transcellular. Cl-/formate and Cl-/oxalate exchangers have been identified as mechanisms of uphill Cl- entry across the apical membrane. For steady-state Cl- absorption to occur by these mechanisms, formate and oxalate must recycle from lumen to cell. Recent studies indicate that recycling of formate occurs by H(+)-coupled formate transport in parallel with Na+/H+ exchange, whereas oxalate recycling takes place by oxalate/sulfate exchange in parallel with Na(+)-sulfate cotransport. The predominant route for Cl- exit across the basolateral membrane is via Cl- channels. Unresolved issues include the adequacy of formate recycling to sustain Cl- absorption by Cl-/formate exchange, the existence and contributions of additional mechanisms for apical Cl entry and basolateral Cl- exit, and the relative magnitudes of transcellular and paracellular transport under physiological conditions. In addition, the molecular identification and mechanisms of regulation of the Cl-/formate and Cl-/oxalate exchangers remain to be defined.

Urate transport in the proximal tubule: in vivo and vesicle studies

1985 ◽  
Vol 249 (6) ◽  
pp. F789-F798 ◽  
Author(s):  
A. M. Kahn ◽  
E. J. Weinman
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Anion Exchanger ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Transport Processes ◽  
Basolateral Membrane Vesicles ◽  
Urate Transport ◽  
Rat Proximal Tubule

The transport of urate in the mammalian nephron is largely confined to the proximal tubule. Depending on the species, net reabsorption or net secretion is observed. The rat, like the human and the mongrel dog, demonstrates net reabsorption of urate and has been the most extensively studied species. The unidirectional reabsorption and secretion of urate in the rat proximal tubule occur via a passive and presumably paracellular route and by a mediated transcellular route. The reabsorption of urate, and possibly its secretion, can occur against an electrochemical gradient. A variety of drugs and other compounds affect the reabsorption and secretion of urate. The effects of these agents depend on their site of application (luminal or blood), concentration, and occasionally their participation in transport processes that do not have affinity for urate. Recent studies with renal brush border and basolateral membrane vesicles from the rat and brush border vesicles from the dog have determined the mechanisms for urate transport across the luminal and antiluminal membranes of the proximal tubule cell. Brush border membrane vesicles contain an anion exchanger with affinity for urate, hydroxyl ion, bicarbonate, chloride, lactate, p-aminohippurate (PAH), and a variety of other organic anions. Basolateral membrane vesicles contain an anion exchanger with affinity for urate and chloride but not for PAH. Both membrane vesicle preparations also permit urate translocation by simple diffusion. A model for the transcellular reabsorption and secretion of urate in the rat proximal tubule is proposed. This model is based on the vesicle studies, and it can potentially explain the majority of urate transport data obtained with in vivo techniques.

Regulation of electrolyte and fluid secretion in salivary acinar cells

1992 ◽  
Vol 263 (6) ◽  
pp. G823-G837 ◽  
Author(s):  
B. Nauntofte
Keyword(s):  
Ionic Composition ◽  
Basolateral Membrane ◽  
Acinar Cells ◽  
Fluid Secretion ◽  
Receptor Activation ◽  
Exchange Mechanism ◽  
Luminal Membrane ◽  
Net Uptake ◽  
Cl Channels ◽  
Simultaneous Activation

The primary secretion from exocrine gland cells is a fluid rich in Na+ and Cl- with a plasmalike ionic composition. Activation of specific receptors on the plasma membrane by hormones and neurotransmitters, which leads to activation of the phosphoinositol metabolism, results in release of Ca2+ from internal Ca2+ stores. Intracellular free Ca2+ concentration ([Ca2+]i) then rises simultaneously at both the basolateral and luminal parts of the acinar cell, reaching maximum values within 1 s after stimulation. In parotid acinar cells, increased [Ca2+]i activates the opening of maxi K+ channels located on the basolateral membrane and Cl- channels presumably located on the luminal membrane, resulting in rapid loss of K+ and Cl- and water and cell shrinkage. Extracellular electroneutrality is maintained by a paracellular Na+ flux into the lumen. Because of the simultaneous activation of K+ and Cl- channels, secretion occurs at a virtually constant membrane potential of about -60 mV. After maximal muscarinic cholinergic stimulation, loss of K+, Cl-, and water results in an approximate 25% reduction in cell volume within 10-15 s after receptor activation. Concomitant with loss of Cl-, there is a loss of HCO3- from the cell, causing a decrease in intracellular pH of 0.1 pH units because of the carbonic anhydrase-mediated conversion of CO2 into H+ and HCO3-. H+ generated from the metabolism and HCO3- production is compensated for by extrusion of H+ by a Na(+)-H+ exchange mechanism, which is responsible for approximately 75% of net Na+ gain that occurs after stimulation. Increased [Na+]i activates the Na(+)-K+ pump, which in turn extrudes Na+ from the cells. In both the unstimulated and stimulated states, cellular production of HCO3- can drive a net uptake of Cl- via the Cl(-)-HCO3- exchange mechanism operating in parallel with the Na(+)-H+ exchanger. The operation of the Cl(-)-HCO3- exchanger is, together with a Na(+)-K(+)-2Cl- cotransport system, essential for maintainance of a high [Cl-]i both in the unstimulated state and during Cl- reuptake.

Chloride transport by the cortical and outer medullary collecting duct

1987 ◽  
Vol 253 (2) ◽  
pp. F203-F212 ◽  
Author(s):  
V. L. Schuster ◽  
J. B. Stokes
Keyword(s):  
Chloride Transport ◽  
Collecting Duct ◽  
Exchange Process ◽  
Basolateral Membrane ◽  
Fine Tuning ◽  
Transport Systems ◽  
Acid Base ◽  
Intercalated Cell ◽  
Cl Channel ◽  
Collecting Tubule

The processes by which chloride is transported by the cortical and outer medullary collecting tubule have been most extensively studied using in vitro microperfusion of rabbit tubules. Chloride appears to be transported by three major mechanisms. First, Cl can be actively reabsorbed by an electroneutral Cl-HCO3 exchanger localized to the apical membrane of the HCO3-secreting (beta-type) intercalated cell. Cl exits this cell via a basolateral Cl channel. This anion exchange process can also operate in a Cl self-exchange mode, is stimulated acutely by beta-adrenergic agonists and cAMP, and is regulated chronically by in vivo acid-base status. Second, Cl can diffuse passively down electrochemical gradients via the paracellular pathway. Although this pathway does not appear to be selectively permeable to Cl, it is large enough to allow for significant passive reabsorption. Third, Cl undergoes recycling across the basolateral membrane of the H+-secreting (alpha-type) intercalated cell. HCO3 exit from this cell brings Cl into the cell via electroneutral Cl-HCO3 exchange; Cl then exits the cell via a Cl channel. Cl transport is thus required for acidification and alkalinization of the urine. Both of these processes exist in the cortical collecting tubule. Their simultaneous operation allows fine tuning of acid-base excretion. In addition, these transport systems, when functioning at equal rates, effect apparent electrogenic net Cl absorption without changing net HCO3 transport. These systems may play an important role in regulating Cl balance.

Nonselective cation and Cl channels in luminal membrane of the marginal cell

1993 ◽  
Vol 265 (1) ◽  
pp. C72-C78 ◽  
Author(s):  
H. Sunose ◽  
K. Ikeda ◽  
Y. Saito ◽  
A. Nishiyama ◽  
T. Takasaka
Keyword(s):  
Single Channel ◽  
Patch Clamp Technique ◽  
Cl Channel ◽  
Luminal Membrane ◽  
Cl Channels ◽  
Cytoplasmic Acidification ◽  
Marginal Cells ◽  
Single Channel Currents ◽  
Channel Currents ◽  
Linear Conductance

Single-channel currents of the luminal membrane of marginal cells dissected from the guinea pig cochlea were investigated using the patch-clamp technique. Nonselective cation channels having a linear conductance of 27 pS were activated by depolarization, cytoplasmic Ca2+, and cytoplasmic acidification. Cytoplasmic ATP inactivated the channel. A mixture of 3-isobutyl-1-methylxanthine and forskolin activated a small-conductance Cl channel in the cell-attached mode. On excision in the inside-out mode, the Cl channel was inactivated, but it was reactivated by a cytoplasmic catalytic subunit of protein kinase A with ATP. This Cl channel had a linear conductance of 12 pS, and its activity was little affected by voltage. The sequence of permeation by anions was Br- > Cl > I-. The Cl channel blocker diphenylamine-2-carboxylic acid (3 mM) completely blocked the channel, but 5-nitro-2-(3-phenylpropylamino)-benzoic acid (50 microM) blocked it only partially. The above-mentioned characteristics are similar to those of the well-demonstrated Cl- channel, cystic fibrosis transmembrane regulator.

Psoralens: novel modulators of Cl- secretion

1997 ◽  
Vol 272 (3) ◽  
pp. C976-C988 ◽  
Author(s):  
D. C. Devor ◽  
A. K. Singh ◽  
R. J. Bridges ◽  
R. A. Frizzell
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Primary Cultures ◽  
Receptor Activation ◽  
Sustained Response ◽  
Rat Colon ◽  
Cl Secretion ◽  
Cl Channel ◽  
Cl Channels ◽  
Cl Conductance

We evaluated effects of psoralens on Cl- secretion (short-circuit current, I(sc)) across T84 monolayers. Methoxsalen failed to increase I(sc). Several observations suggest that psoralens open cystic fibrosis transmembrane conductance regulator Cl- channels. 1) After activation of the Ca2+-dependent basolateral membrane K+ channel (K(Ca)) by 1-ethyl-2-benzimidazolinone or thapsigargin, methoxsalen (10 microM) further increased I(sc). 2) When added before carbachol (CCh), methoxsalen potentiated the I(sc) response to CCh, as predicted, if it increased apical Cl- conductance. 3) After establishment of a mucosal-to-serosal Cl- gradient and permeabilization of basolateral membrane with nystatin, psoralens increased Cl- current, which was inhibited by glibenclamide. In contrast, neither TS-TM calix[4]arene nor Cd2+, inhibitors of outwardly rectifying Cl- channels and the ClC-2 Cl-channel, respectively, inhibited psoralen-induced Cl- current. In contrast to their effects on Cl- conductance, psoralens failed to significantly affect basolateral membrane K+ conductance; subsequent addition of 1-ethyl-2-benzimidazolinone induced a large increase in K+ conductance. Also, in excised patches, methoxsalen failed to activate K(Ca). In addition to potentiating the peak response to CCh, psoralens induced a secondary, sustained response. Indeed, when added up to 60 min after return of CCh-induced I(sc) to baseline, psoralens induced a sustained I(sc). This sustained response was inhibited by atropine, demonstrating the requirement for continuous muscarinic receptor activation by CCh. This sustained response was inhibited also by verapamil, removal of bath Ca2+, and charybdotoxin. These results suggest that return of I(sc) to baseline after CCh stimulation is not due to downregulation of Ca2+ influx or K(Ca). Finally, we obtained similar results with psoralens in rat colon and primary cultures of murine tracheal epithelium. On the basis of these observations, we conclude that psoralens represent a novel class of Cl- channel openers that can be used to probe mechanisms underlying Ca2+-mediated Cl- secretion.

A double-membrane model for urinary bicarbonate secretion

1985 ◽  
Vol 249 (4) ◽  
pp. F546-F552 ◽  
Author(s):  
D. L. Stetson ◽  
R. Beauwens ◽  
J. Palmisano ◽  
P. P. Mitchell ◽  
P. R. Steinmetz
Keyword(s):  
Channel Blocker ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Ultrastructural Examination ◽  
Transport Pathway ◽  
Anion Conductance ◽  
Luminal Membrane ◽  
Disulfonic Stilbene ◽  
Ph Stat

To define the transport pathway for HCO-3 secretion (JHCO3) across the apical and basolateral membranes of turtle bladder, we examined the effects of cAMP, isobutylmethylxanthine (IBMX), the Cl- channel blocker 9-anthroic acid (9-AA), and the disulfonic stilbene DIDS (4,4'-diisothiocyanostilbene-2,2'-sulfonic acid) on the electroneutral and electrogenic components of JHCO3. Total JHCO3 was measured by pH stat titration of the mucosal compartment after Na+ absorption and H+ secretion were abolished by ouabain and a delta pH, respectively. Addition of cAMP or IBMX increased total JHCO3 and induced a short-circuit current (ISC), accounting for a large part of JHCO3; net Cl- absorption was reduced. Mucosal 9-AA inhibited the IBMX-induced electrogenic component of JHCO3, whereas mucosal DIDS inhibited the electroneutral component and acetazolamide reduced both. We suggest that HCO-3 is generated within the cell by a Na-independent primary active acid-base transport at the basolateral membrane (H+ extrusion into the serosal compartment). Cellular HCO-3 accumulation drives JHCO3 via a Cl-HCO3 exchanger at the luminal membrane. IBMX and cAMP activate a 9-AA-sensitive anion conductance parallel to the exchanger. The apparent reversal of the transport elements between the two cell membranes (compared with H+-secreting cells) led to an ultrastructural examination of the carbonic anhydrase-rich cells.

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