Regulation of the renal Na+−H+ exchanger by protein phosphorylation. Kidney Int

University of Texas Medical School, Houston 77025.
Kidney International (Impact Factor: 8.56). 11/1989; 36(4):519-25. DOI: 10.1038/ki.1989.226
Source: PubMed


Starting from observations in intact cells and extending to studies in native membranes and solubilized membrane proteins, a significant body of evidence has been accumulated to indicate that some of the short-term regulatory influences on the Na+-H+ exchanger in the apical membrane of the proximal convoluted tubule act via protein phosphorylation mediated by specific protein kinases. Protein phosphorylation mediated by PKA inhibits the Na+-H+ exchanger while that mediated by PKC stimulates activity. The effect of PKA and PKC on the Na+-H+ exchanger in native membranes and in solubilized brush border membrane proteins appears to be consistent with most of the published observations in intact cells. Further studies using solubilized, renal brush border membrane proteins indicated that protein phosphorylation mediated by CaM-kinase II inhibited the activity of the Na+-H+ exchanger. The physiologic significance of this observation in intact cells remains to be determined. It is hoped that the types of experimental approaches outlined in this review will yield additional insights into the structure of the Na+-H+ exchanger and to a clearer understanding of its physiologic regulation.

2 Reads
  • Source
    • "Such findings support a previous notion that the effects of cAMP can not be explained simply by a nonselective inhibition of ion-coupled transport systems (Saccomani et al., 1990). Such membrane-protein systems, however, can be kept inactivated by phosphorylation from cAMP-dependent kinase (Weinman etal., 1989). Furthermore, as a hypothesis, nuclear proteins such as regulatory trans-acting factors, may also be phosphorylated and attenuated by similar enzyme events (Taylor, 1989). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Physiologic concentrations of angiotensin II (AII) can induce cellular hypertrophy in murine proximal tubular epithelium (MCT cells). This response is characterized by an increase in cell size, new protein synthesis, and by the secretion of new basement membrane type IV collagen in the absence of cellular proliferation. The present study was undertaken to evaluate the second messengers of these AII-induced cellular events with special reference to the increase in type IV collagen secretion. In initial experiments we observed that pretreatment of MCT cells with agents that increase concentrations of intracellular cAMP, like forskolin, dibutyryl cAMP, and isobutyl-methyl-xanthine abolish AII-induced amino acid incorporation, but have no effect on control cells or on their proliferation. In addition, 10(-8) M AII significantly decreased the concentration of intracellular cAMP. Phorbolesters were without significant effect on the hypertrophy or proliferation of AII-stimulated MCT cells or their rested controls. The transfection of MCT cells with reporter genes containing regulatory elements for type IV collagen revealed that the stimulatory effects of AII on collagen type IV depend, at least to some extent, on an increase in gene transcription. Agents increasing intracellular cAMP concentrations inhibited the AII-induced increase in transcription and secretion of collagen type IV, but had no effect on MCT cells grown in media without AII. Our findings provide evidence that AII-induced changes in tubular epithelium leading to the secretion of type IV collagen are mediated by a decrease in intracellular cAMP.
    Cell regulation 04/1991; 2(3):219-27. DOI:10.1091/mbc.2.3.219
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Diese Arbeit befaßt sich mit intrazellulären Regulationsmechanismen der Cyclosporin A-assoziierten arteriellen Hypertonie und Nephrotoxizität. Die Cyclosporin A-assoziierte arterielle Hypertonie kommt zum Großteil durch eine vermehrte Na+-Reabsorption des proximalen Tubulus zustande. Ursächlich dafür scheint eine gesteigerte Aktivität des luminalen Na+-H+-Austauschers (NHE-3) zu sein. Die Untersuchungen wurden mit Hilfe der "Prepulse"-Technik in einem in vitro Modell polarisierter LLC-PK1/PKE20-Zellen durchgeführt. Mittels dieser Technik wurden fluoreszenz-mikroskopisch Änderungen des intrazellulären pH-Wertes pro Minute (D[pH]i/min) gemessen. Diese induzierten pH-Änderungen wurden als Realkalisierungsrate bezeichnet. Die Realkalisierungsrate entspricht der Aktivität des NHE-3. Cyclosporin A bewirkt in LLC-PK1/PKE20-Zellen eine NHE-3-Aktivitätssteigerung. Ca2+ als einer der wichtigsten intrazellulären Botenstoffe beeinflußt die Na+-Reabsorption des proximalen Tubulus. Eine gesteigerte NHE-3-Aktivität beruht auf einer Erhöhung der intrazellulären Ca2+-Konzentration [Ca2+]i. In LLC-PK1/PKE20-Zellen wurde ursächlich dafür eine Freisetzung von Ca2+ aus intrazellulären Speichern nachgewiesen. Diese Ca2+-Freisetzung macht 30% der [Ca2+]i-Erhöhung aus, 60% werden durch Einstrom in die Zelle aus dem Extrazellulärraum bedingt. Veränderungen der [Ca2+]e hatten jedoch keinen Einfluß auf die Cyclosporin A-assoziierte NHE-3-Aktivität. Angiotensin II führt ebenfalls zu einer gesteigerten Na+-Reabsorption des proximalen Tubulus. Potenzierende Effekte von Cyclosporin A auf die Angiotensin II-vermittelte Aktivierung des NHE-3 konnten nicht festgestellt werden. Losartan zeigte ebenfalls keinen Einfluß auf die Cyclosporin A-assozierte NHE-3-Aktivität. Eine Wirkung von Cyclosporin A auf Angiotensin II-vermittelte Effekte am proximalen Tubulus scheint daher unwahrscheinlich. Ebenso konnte ein Einfluß von Cyclosporin A auf die intrazelluläre Proteinkinase C ausgeschlossen werden. Dagegen wurde nachgewiesen, daß Cyclosporin A die von der Proteinkinase A-induzierte NHE-3-Hemmung in 50% der Fälle antagonisierte. Dies kann im Sinne eines indirekt inhibierenden Effektes von Cyclosporin A auf die NHE-3-Aktivität erklärt werden. Zusammenfassend kann gesagt werden, daß die Cyclosporin A-assoziierte Steigerung der NHE-3-Aktivität auf einer Ca2+-abhängigen, indirekt inhibierenden Wirkung des Medikamentes auf Proteinkinasen vom Typ A beruht.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Aside from the normal, sporadic turnover of epithelial cells along the adult nephron, most somatic cells in the kidney do not divide, or if they are obligated to respond to an external stimulus, there seems to be less hyperplasia in preference for cellular hypertrophy. A variety of pathophysiologic stimuli which provide temporary or permanent fixed reductions in renal function often result, for example, in compensatory enlargement of the kidney, principally in the tubulointerstitium [1]. Such adaptive responses are thought to provide a mechanism for redressing initial damage, as well as providing for a limited restoration of function. The renal hemodynamic alterations associated with these events, like increases in single nephron glomerular filtration rate (SNGFR) and glomerular blood flow, have been extensively reviewed elsewhere [2, 3], Changes in the size of the tubular nephron, as well as subsequent, late renal fibrosis have traditionally been considered a response to modifications in the mechanics of filtration—the so-called work hypothesis [4]. There is, however, alternative evidence in animals [5, 6], and humans [7], that the cellular processes of compensatory renal enlargement, themselves might share in the responsibility for the continued, long-term loss in remaining nephrons.
    Kidney International 04/1991; 39(3):401-20. DOI:10.1038/ki.1991.52 · 8.56 Impact Factor
Show more