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  • 1
    Electronic Resource
    Electronic Resource
    REGULATION OF Na/Pi TRANSPORTER IN THE PROXIMAL TUBULE (2003)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 65 (2003), S. 531-542 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract The physiological tuning and pathophysiological alterations of renal proximal reabsorption of inorganic phosphate can be ascribed to the net amount of the Na/Pi-cotransporter NaPi-IIa localized in the brush border membrane. The net amount of NaPi-IIa appears to be the result of an endocytotic rate regulated by a complex network of different protein kinases. New approaches demonstrated that NaPi-IIa is part of heteromeric protein complexes, organized by PDZ (postsynaptic protein PSD95, Drosophila junction protein Disc-large, tight junction protein ZO-1) proteins. Such complexes are thought to play important roles in the apical positioning and regulated endocytosis of NaPi-IIa and therefore such interactions have to be considered when explaining proximal phosphate ion reabsorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.65.042902.092424
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  • 2
    Electronic Resource
    Electronic Resource
    Cotransport Systems for Inorganic Sulfate and Phosphate in Small Intestine and Renal Proximal Tubule (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 456 (1985), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1985.tb14859.x
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  • 3
    Electronic Resource
    Electronic Resource
    ATP-DEPENDENT Ca2+ UPTAKE IN ISOLATED HEPATIC PLASMA MEMBRANE VESICLES (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 402 (1982), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1982.tb25762.x
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  • 4
    Electronic Resource
    Electronic Resource
    Apical and basolateral effects of PTH in OK cells: Transport inhibition, messenger production, effects of pertussis toxin, and interaction with a PTH analog (1991)
    Springer
    The journal of membrane biology 124 (1991), S. 227-237 
    Details
    ISSN: 1432-1424
    Keywords: cell polarity ; pertussis toxin ; parathyroid hormone (PTH) ; PTH-analogs ; internal messengers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The cellular distribution (apicalvs. basolateral) of parathyroid hormone (PTH) signal transduction systems in opossum kidney (OK) cells was evaluated by measuring the action of PTH on apically located transport processes (Na/Pi cotransport and Na/H exchange) and on the generation of intracellular messengers (cAMP and IP3). PTH application led to immediate inhibition of Na/H-exchange without a difference in dose/response relationships between apical and basolateral cell-surface hormone addition (halfmaximal inhibition at ≈5×10−10 m). PTH required 2–3 hr for maximal inhibition of Na/Pi cotransport with a half-maximal inhibition occurring at ≈×10−12 m for apical application. PTH addition to either side of the monolayer produced a dose-dependent production of both cAMP and IP3. Half-maximal activation of IP3 was at about 7×10−12 m PTH and displayed no differences between apical and basolateral hormone addition, while cAMP was produced with a half maximal concentration of 7×10−9 m for apical PTH application and 10−9 m for basolateral administration. The PTH analog [nle8.18, tyr34]PTH(3-34), (nlePTH), produced partial inhibition of Na/Pi cotransport (agonism) with no difference between apical and basolateral application. When applied as a PTH antagonist, nlePTH displayed dose-dependent antagonism of PTH inhibition of Na/Pi cotransport on the apical surface, failing to have an effect on the basolateral surface. Independent of addition to the apical or basolateral cell surface, nlePTH had only weak stimulatory effect on production of cAMP, whereas high levels of IP3 could be measured after addition of this PTH analog to either cell surface. Also an antagonistic action of nlePTH on PTH-dependent generation of the internal messengers, cAMP and IP3, was observed; at the apical and basolateral cell surface nlePTH reduced PTH-dependent generation of cAMP, while PTH-dependent generation of IP3 was only reduced by nlePTH at the apical surface. Pertussis toxin (PT) preincubation produced an attenuation of both PTH-dependent inhibition of Na/Pi cotransport and IP3 generation while producing an enhancement of PTH-dependent cAMP generation; these effects displayed no cell surface polarity, suggesting that PTH action through either adenylate cyclase or phospholipase C was transduced through similar sets of G-proteins at each cell surface. It is concluded that apparent receptor activities with high and low affinity for PTH exist on both cell surfaces; those with apparent high affinity seem to be coupled preferentially to phospholipase C and those with apparent low affinity to adenylate cyclase. The differences in apparent affinity of receptor events coupled to adenylate cyclase and the differences in PTH/nlePTH interaction on the two cell surfaces are suggestive of the existence of differences in apparent PTH-receptor activities on the two cell surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01994356
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  • 5
    Electronic Resource
    Electronic Resource
    Measurements of intracellular pH in single LLC-PK1 cells: Recovery from an acid load via basolateral Na+/H+ exchange (1987)
    Springer
    The journal of membrane biology 97 (1987), S. 63-78 
    Details
    ISSN: 1432-1424
    Keywords: Na+/H+ exchange ; intracellular pH ; renal cell culture ; LLC-PK1 ; membrane polarity ; ethylisopropylamiloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary LLC-PK1 cells (a continuous epithelioid cell line with renal characteristics) are examined by microspectrofluorometry as single cells, in order to determine the mechanism of intracellular pH (pH i ) recovery from an acid load imposed by ammonium preincubation and removal (NH4 prepulse). Initial experiments evaluate the intracellular K+ levels through a null point analysis of total cellular K+ with flame photometry. The response of BCECF (a pH-sensitive fluorescent dye) is then calibrated, using saturating concentrations of nigericin to cause defined changes in pH i . For experiments with the microspectrofluorometer, LLC-PK1 cells were grown on either glass coverslips or filters (the latter attached to plastic coverslips with a hole under the filter). The cells on glass coverslips demonstrate a Na+-dependent recovery from an (NH4 prepulse) acid load which is sensitive to 1 μM ethylisopropylamiloride. They also demonstrate a ‘set point’ of activation of Na+/H+ exchange. When examined for changes in pH i due to changes in membrane potential, plasma membrane proton conductance could not be detected at resting pH i . Cells grown on filters also demonstrate a pH i recovery from an acid load which is Na+ dependent and ethylisopropylamiloride sensitive, but in this configuration, the majority of cells (22/23 preparations) require Na+ at the basolateral membrane for rapid pH i recovery. The morphology and polarity of the cells grown on permeable supports appears normal at the electron-microscopic level. The results are not affected by changes in cell seeding density or collagen treatment of the filters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869615
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  • 6
    Electronic Resource
    Electronic Resource
    Na+/H+-exchange in A6 cells: Polarity and vasopressin regulation (1992)
    Springer
    The journal of membrane biology 130 (1992), S. 105-114 
    Details
    ISSN: 1432-1424
    Keywords: Na+/H+-exchange ; protein kinase A ; protein kinase C ; vasopressin ; distal tubule ; tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have analyzed the mechanism of Na+-dependent pHi; recovery from an acid load in A6 cells (an amphibian distal nephron cell line) by using the intracellular pH indicator 2′7′-bis(2-carboxyethyl)5, 6 carboxyfluorescein (BCECF) and single cell microspectrofluorometry. A6 cells were found to express Na+/H+-exchange activity only on the basolateral membrane: Na+/H+-exchange activity follows simple saturation kinetics with an apparent K mfor Na+ of approximately 11 mm; it is inhibited in a competitive manner by ethylisopropylamiloride (EIPA). This Na+/H+-exchange activity is inhibited by pharmacological activation of protein kinase A (PKA) as well as of protein kinase C (PKC). Addition of arginine vasopressin (AVP) either at low (subnanomolar) or at high (micromolar) concentrations inhibits Na+/H+-exchange activity; AVP stimulates IP3 production at low concentrations, whereas much higher concentrations are required to stimualte cAMP formation. These findings suggest that in A6 cells (i) Na+/H+-exchange is located in the basolateral membrane and (ii) PKC activation (heralded by IP3 turnover) is likely to be the mediator of AVP action at low AVP concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231889
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  • 7
    Electronic Resource
    Electronic Resource
    Functional roles of Na+ and H+ in SO 4 2− transport by rabbit ileal brush border membrane vesicles (1984)
    Springer
    The journal of membrane biology 78 (1984), S. 177-186 
    Details
    ISSN: 1432-1424
    Keywords: membrane vesicles ; rabbit ileum ; rabbit proximal tubule ; brush border ; sulphate transport ; Na+ dependence ; H+ dependence ; cooperativity ; sigmoidal transport ; cotransport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Sulphate uptake by rabbit ileal brush border membrane vesicles was stimulated by a transmembrane sodium gradient ([Na+] o 〉[Na+] i ), but not by a similar potassium gradient.35SO 4 2− influx (J oi SO4 ) from outside (o) to inside (i) these vesicles was a hyperbolic function of [SO 4 2− ] o and the affinity constant for anion transport was strongly influenced by [Na+] o (100mm Na+,K t SO4 =0.52mm SO 4 2− ; 10mm Na+,K t SO4 =4.32mm SO 4 2− ).J t SO4 was a sigmoidal function of [Na+] o at pH 7.4 for both low (0.2m) and high (4.0mm) [SO 4 2− ] o . The Na+-dependency ofJ t SO4 was examined at pH 6.0, 7.4, and 8.0 (same pH inside and outside). At pH 6.0 and 7.4 sigmoidal Na+-dependentJ t SO4 exhibited nonlinear Eadie-Hofstee plots indicative of a transport mechanism capable of binding a variable number of sodium ions over the [Na+] o range used. Hill plots of anion transport under these conditions displayed slopes near unity at low [Na+] o and slopes approximating 2.0 at higher cation concentrations. At pH 8.0, Na+-dependentJ t SO4 was hyperbolic and showed linear Eadie-Hofstee and Hill plots, the latter with a single slope near 1.0. When a H+ gradient was imposed across the vesicle wall (pH i =8.0, pH o =6.0), Na+-dependentJ t SO4 was hyperbolic and significantly increased at each [Na+] o over values observed using bilateral pH 8.0. In contrast, a H+ gradient oriented in the opposite direction (pH i =6.0, pH o =8.0) led to Na+-dependentJ t SO4 that was sigmoidal and significantly lower at each [Na+] o than values found using bilateral pH 6.0. Electrogenicity ofJ t SO4 at pH 8.0 for both high and low [Na+] o was demonstrated by using a valinomycin-induced transmembrane electrical potential difference. At pH 6.0, electrogenicJ t SO4 occurred only at low [Na+] o (5mm); anion transfer was electroneutral at 50mm Na+. A model is proposed for proton regulation of sodium sulphate cotransport where flux stoichiometry is controlled by [H+] i and sodium binding affinity is modified by [H+] o . Preliminary experiments with rabbit proximal tubular brush border membrane vesicles disclosed similarJ t SO4 kinetic properties and a common transport mechanism may occur in both tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01925966
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  • 8
    Electronic Resource
    Electronic Resource
    Role of calcium and calmodulin in the regulation of the rabbit ileal brush-border membrane Na+/H+ antiporter (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 207-215 
    Details
    ISSN: 1432-1424
    Keywords: calcium ; calmodulin ; absorption ; ileum ; brush-border vesicle ; phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In rabbit ileum, Ca2+/calmodulin (CaM) appears to be involved in physiologically inhibiting the linked NaCl absorptive process, since inhibitors of Ca2+/CaM stimulate linked Na+ and Cl− absorption. The role of Ca2+/CaM-dependent phosphorylation in regulation of the brush-border Na+/H+ antiporter, which is believed to be part of the neutral linked NaCl absorptive process, was studied using purified brush-border membrane vesicles, which contain both the Na+/H+ antiporter and Ca2+/CaM-dependent protein kinase(s) and its phosphoprotein substrates. Rabbit ileal villus cell brush-border membrane vesicles were prepared by Mg precipitation and depleted of ATP. Using a freezethaw technique, the ATP-depleted vesicles were loaded with Ca2+, CaM, ATP and an ATP-regenerating system consisting of creatine kinase and creatine phosphate. The combination of Ca2+/CaM and ATP inhibited Na+/H+ exchange by 45±13%. This effect was specific since Ca2+/CaM and ATP did not alter diffusive Na+ uptake, Na+-dependent glucose entry, or Na+ or glucose equilibrium volumes. The inhibition of the Na+/H+ exchanger by Ca2+/CaM/ATP was due to an effect on theV max and not on theK m for Na+. In the presence of CaM and ATP, Ca2+ caused a concentration-dependent inhibition of Na+ uptake, with an effect 50% of maximum occurring at 120nm. This Ca2+ concentration dependence was similar to the Ca2+ concentration dependence of Ca2+/CaM-dependent phosphorylation of specific proteins in the vesicles. The Ca2+/CaM/ATP-inhibition of Na+/H+ exchange was reversed by W13, a Ca2+/CaM antagonist, but not by a hydrophobic control, W12, or by H-7, a protein kinase C antagonist. we conclude that Ca2+, acting through CaM, regulates ileal brush-border Na+/H+ exchange, and that this may be involved in the regulation of neutral linked NaCl absorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871735
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  • 9
    Electronic Resource
    Electronic Resource
    Vasopressin-dependent control of basolateral Na/H-exchange in highly differentiated A6-cell monolayers (1993)
    Springer
    The journal of membrane biology 135 (1993), S. 209-216 
    Details
    ISSN: 1432-1424
    Keywords: Na+/H+ exchange ; Protein kinases ; cAMP ; Vasopressin ; Distal tubule ; Tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We have used a well-differentiated A6-cell preparation (A6-C1) to study cellular location and vasopressin control of Na/H-exchange activity. After cell acidification, cell pHi (measured by BCECF-fluorescence) only recovered by the addition of Na medium to the basolateral cell surface; this pHi recovery was inhibited by dimethylamiloride (2 μm) consistent with basolateral location of Na/H-exchange activity. Addition of vasopressin produced stimulation of Na/H-exchange activity and increased the affinity of the exchanger for Na+. Stimulation of Na/H exchange was mimicked by pharmacological activation of protein kinase A (forskolin, 8-Br-cAMP) and not by pharmacological activation of protein kinase C (TPA). It is concluded that basolaterally located Na/H-exchange in A6-C1 cells is activated by vasopressin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211092
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  • 10
    Electronic Resource
    Electronic Resource
    Apical and basolateral Na/H exchange in cultured murine proximal tubule cells (MCT): Effect of parathyroid hormone (PTH) (1992)
    Springer
    The journal of membrane biology 130 (1992), S. 205-217 
    Details
    ISSN: 1432-1424
    Keywords: Na/H exchange ; Na/P i cotransport ; cAMP ; protein kinase C ; intracellular Ca2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Kidney proximal tubule Na/H exchange is inhibited by PTH. To analyze further the cellular mechanisms involved in this regulation we have used MCT cells (a culture of SV-40 immortalized mouse cortical tubule cells) grown on permeant filter supports. Na/H exchange was measured using single cell fluorescence microscopy (BCECF) and phosphate transport (measured for comparisons) by tracer techniques. MCT cells express apical and basolateral Na/H exchangers which respond differently to inhibition by ethylisopropylamiloride and by dimethylamiloride, the basolateral membrane transporter being more sensitive. Apical membrane Na/H exchange was inhibited by PTH (10−8 m; by an average of 25%); similar degrees of inhibition were observed when cells were exposed either to forskolin, 8-bromo-cAMP or phorbol ester. Basolateral membrane Na/H exchange was stimulated either by incubation with PTH (to 129% above control levels) or by addition of phorbol ester (to 120% above control levels); it was inhibited after exposure to either forskolin or 8-bromo-cAMP. The above effects of PTH and phorbol ester (apical and basolateral) were prevented by preincubation of cells with protein kinase C antagonists, staurosporine and calphostin C; both compounds did not affect forskolin or 8-bromo-cAMP induced effects. PTH also inhibited apical Na-dependent phosphate influx (29% inhibition at 10−8 m); it had no effect on basolateral phosphate fluxes (Na-dependent and Na-independent). Incubation with PTH (10−8 m) resulted in a rapid and transient increase in [Ca2+] i (measured with the fluorescent indicator, fura-2), due to stimulation of a Ca2+ release from intracellular stores. Exposure of MCT cells to PTH did not elevate cellular levels of cAMP. Taken together, these results suggest that PTH utilizes in MCT cells the phospholipase C/protein kinase C pathway to differently control Na/H exchangers (apical vs. basolateral) and to inhibit apical Na/P i cotransport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00240478
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