Publications

• Biochemical properties of the Na+/H+ exchange system in rat brain synaptosomes. Interdependence of internal and external pH control of the exchange activity.

  Jean T., Frelin C., Vigne P., Barbry P., Lazdunski M.

  Properties of the Na+/H+ exchange system in synaptosomes have been studied primarily by using acridine orange fluorescence to follow H+ efflux. Results obtained from 22Na+ uptake experiments and [3H]ethylpropylamiloride binding experiments are also presented for comparison. The basal properties of ... >> More

  Properties of the Na+/H+ exchange system in synaptosomes have been studied primarily by using acridine orange fluorescence to follow H+ efflux. Results obtained from 22Na+ uptake experiments and [3H]ethylpropylamiloride binding experiments are also presented for comparison. The basal properties of the Na+/H+ antiport in synaptosomes are similar to those found in other systems; (i) the stoichiometry of Na+/H+ exchange is 1:1; (ii) Li+ can be successfully substituted for Na+; its affinity for the exchanger (KLi+ = 3 mM) is higher than that of Na+ (KNa+ = 12 mM), but the maximal rate of H+ efflux in the presence of Li+ is about 3 times lower than the maximal rate of H+ efflux in the presence of Na+; and (iii) the Na+/H+ antiport is inhibited by amiloride derivatives with the rank order:ethylisopropylamiloride greater than ethylpropylamiloride greater than amiloride greater than benzamil. The most important finding of this paper is that the external pH dependence of the synaptosomal Na+/H+ antiport is controlled by the value of internal pH and vice versa. For example apparent pHo values for half-maximum activation of the Na+/H+ exchanger are pHo = 7.12 when pHi = 6.4 and pHo = 7.95 when pHi = 7.3. Therefore, a 0.9 pH unit increase in internal pH produces a shift of at least a 0.83 pH unit in the external pH dependence. In addition, changing pHo from 7.75 to 8.50 also shifts the half-maximum pHi value for activation of the Na+/H+ antiport from 6.67 to 7.54. << Less

  J Biol Chem 260:9678-9684(1985) [PubMed] [EuropePMC]

• Cytoplasmic pH regulation in thymic lymphocytes by an amiloride-sensitive Na+/H+ antiport.

  Grinstein S., Cohen S., Rothstein A.

  The mechanisms underlying cytoplasmic pH (pHi) regulation in rat thymic lymphocytes were studied using trapped fluorescein derivatives as pHi indicators. Cells that were acid-loaded with nigericin in choline+ media recovered normal pHi upon addition of extracellular Na+ (Nao+). The cytoplasmic alk ... >> More

  The mechanisms underlying cytoplasmic pH (pHi) regulation in rat thymic lymphocytes were studied using trapped fluorescein derivatives as pHi indicators. Cells that were acid-loaded with nigericin in choline+ media recovered normal pHi upon addition of extracellular Na+ (Nao+). The cytoplasmic alkalinization was accompanied by medium acidification and an increase in cellular Na+ content and was probably mediated by a Nao+/Hi+ antiport. At normal [Na+]i, Nao+/Hi+ exchange was undetectable at pHi greater than or equal to 6.9 but was markedly stimulated by internal acidification. Absolute rates of H+ efflux could be calculated from the Nao+-induced delta pHi using a buffering capacity of 25 mmol X liter-1 X pH-1, measured by titration of intact cells with NH4+. At pHi = 6.3, pHo = 7.2, and [Na+]o = 140 mM, H+ extrusion reached 10 mmol X liter-1 X min-1. Nao+/Hi+ exchange was stimulated by internal Na+ depletion and inhibited by lowering pHo and by addition of amiloride (apparent Ki = 2.5 microM). Inhibition by amiloride was competitive with respect to Nao+. Hi+ could also exchange for Lio+, but not for K+, Rb+, Cs+, or choline+. Nao+/Hi+ countertransport has an apparent 1:1 stoichiometry and is electrically silent. However, a small secondary hyperpolarization follows recovery from acid-loading in Na+ media. This hyperpolarization is amiloride- and ouabain-sensitive and probably reflects activation of the electrogenic Na+-K+ pump. At normal Nai+ values, the Nao+/Hi+ antiport of thymocytes is ideally suited for the regulation of pHi. The system can also restore [Na+]i in Na+-depleted cells. In this instance the exchanger, in combination with the considerable cytoplasmic buffering power, will operate as a [Na+]i-regulatory mechanism. << Less

  J Gen Physiol 83:341-369(1984) [PubMed] [EuropePMC]

• Sodium/proton exchange in mouse neuroblastoma cells.

  Moolenaar W.H., Boonstra J., van der Saag P.T., de Laat S.W.

  The sudden addition of Na+ to mouse neuroblastoma cells suspended in Na+-free medium causes a rapid but transient increase in the rate of H+ release from the cells. Li+ can substitute for Na+, but addition of choline, K+, or Ca2+ has no effect. This process has the following properties: it is dist ... >> More

  The sudden addition of Na+ to mouse neuroblastoma cells suspended in Na+-free medium causes a rapid but transient increase in the rate of H+ release from the cells. Li+ can substitute for Na+, but addition of choline, K+, or Ca2+ has no effect. This process has the following properties: it is distinct from metabolic acid production, it does not require ATP, and it saturates at about 40 mM external Na+; it is independent of membrane potential and can be mimicked by addition of the Na+/H+ ionophore monensin to cells in Na+-containing media. In contrast, a net uptake of protons is observed when Na+-loaded cells are suddenly exposed to Na+-free medium. Na+-induced H+ extrusion is accompanied by a rise in intracellular pH, as inferred from an enhanced net uptake of weak acids and from direct pH measurements on lysed cells. Conversely, Na+ uptake by the cells is stimulated upon lowering the intracellular pH with externally applied acetate. Na+-dependent proton transport, intracellular alkalinization, and acetate-stimulated Na+ uptake are completely inhibited by the diuretic amiloride (0.2 mM) and do not occur in digitonin-permeabilized cells. It is concluded that the plasma membrane of neuroblastoma cells contains an electroneutral Na+/H+ exchange system which is involved in the regulation of intracellular pH. << Less

  J Biol Chem 256:12883-12887(1981) [PubMed] [EuropePMC]

• Dissecting the proton transport pathway in electrogenic Na(+)/H(+) antiporters.

  Uzdavinys P., Coincon M., Nji E., Ndi M., Winkelmann I., von Ballmoos C., Drew D.

  Sodium/proton exchangers of the <i>SLC9</i> family mediate the transport of protons in exchange for sodium to help regulate intracellular pH, sodium levels, and cell volume. In electrogenic Na⁺/H⁺ antiporters, it has been assumed that two ion-binding aspartate residues transp ... >> More

  Sodium/proton exchangers of the <i>SLC9</i> family mediate the transport of protons in exchange for sodium to help regulate intracellular pH, sodium levels, and cell volume. In electrogenic Na⁺/H⁺ antiporters, it has been assumed that two ion-binding aspartate residues transport the two protons that are later exchanged for one sodium ion. However, here we show that we can switch the antiport activity of the bacterial Na⁺/H⁺ antiporter NapA from being electrogenic to electroneutral by the mutation of a single lysine residue (K305). Electroneutral lysine mutants show similar ion affinities when driven by [Formula: see text]pH, but no longer respond to either an electrochemical potential ([Formula: see text]) or could generate one when driven by ion gradients. We further show that the exchange activity of the human Na⁺/H⁺ exchanger NHA2 (<i>SLC9B2</i>) is electroneutral, despite harboring the two conserved aspartic acid residues found in NapA and other bacterial homologues. Consistently, the equivalent residue to K305 in human NHA2 has been replaced with arginine, which is a mutation that makes NapA electroneutral. We conclude that a transmembrane embedded lysine residue is essential for electrogenic transport in Na⁺/H⁺ antiporters. << Less

  Proc. Natl. Acad. Sci. U.S.A. 114:E1101-E1110(2017) [PubMed] [EuropePMC]

• Unconventional chemiosmotic coupling of NHA2, a mammalian Na+/H+ antiporter, to a plasma membrane H+ gradient.

  Kondapalli K.C., Kallay L.M., Muszelik M., Rao R.

  Human NHA2, a newly discovered cation proton antiporter, is implicated in essential hypertension by gene linkage analysis. We show that NHA2 mediates phloretin-sensitive Na(+)-Li(+) counter-transport (SLC) activity, an established marker for hypertension. In contrast to bacteria and fungi where H( ... >> More

  Human NHA2, a newly discovered cation proton antiporter, is implicated in essential hypertension by gene linkage analysis. We show that NHA2 mediates phloretin-sensitive Na(+)-Li(+) counter-transport (SLC) activity, an established marker for hypertension. In contrast to bacteria and fungi where H(+) gradients drive uptake of metabolites, secondary transport at the plasma membrane of mammalian cells is coupled to the Na(+) electrochemical gradient. Our findings challenge this paradigm by showing coupling of NHA2 and V-type H(+)-ATPase at the plasma membrane of kidney-derived MDCK cells, resulting in a virtual Na(+) efflux pump. Thus, NHA2 functionally recapitulates an ancient shared evolutionary origin with bacterial NhaA. Although plasma membrane H(+) gradients have been observed in some specialized mammalian cells, the ubiquitous tissue distribution of NHA2 suggests that H(+)-coupled transport is more widespread. The coexistence of Na(+) and H(+)-driven chemiosmotic circuits has implications for salt and pH regulation in the kidney. << Less

  J. Biol. Chem. 287:36239-36250(2012) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.