Cotransport of water by the Na+-K+-2Cl cotransporter NKCC1 in mammalian epithelial cells

Nordic Centre for Water Imbalance Related Disorders, Institute of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.
The Journal of Physiology (Impact Factor: 5.04). 11/2010; 588(Pt 21):4089-101. DOI: 10.1113/jphysiol.2010.194738
Source: PubMed


Water transport by the Na+-K+-2Cl(-) cotransporter (NKCC1) was studied in confluent cultures of pigmented epithelial (PE) cells from the ciliary body of the fetal human eye. Interdependence among water, Na+ and Cl(-) fluxes mediated by NKCC1 was inferred from changes in cell water volume, monitored by intracellular self-quenching of the fluorescent dye calcein. Isosmotic removal of external Cl(-) or Na+ caused a rapid efflux of water from the cells, which was inhibited by bumetanide (10 μm). When returned to the control solution there was a rapid water influx that required the simultaneous presence of external Na+ and Cl(-). The water influx could proceed uphill, against a transmembrane osmotic gradient, suggesting that energy contained in the ion fluxes can be transferred to the water flux. The influx of water induced by changes in external [Cl(-)] saturated in a sigmoidal fashion with a Km of 60 mm, while that induced by changes in external [Na+] followed first order kinetics with a Km of about 40 mm. These parameters are consistent with ion transport mediated by NKCC1. Our findings support a previous investigation, in which we showed water transport by NKCC1 to be a result of a balance between ionic and osmotic gradients. The coupling between salt and water transport in NKCC1 represents a novel aspect of cellular water homeostasis where cells can change their volume independently of the direction of an osmotic gradient across the membrane. This has relevance for both epithelial and symmetrical cells.

Download full-text


Available from: Thomas Zeuthen,
  • Source
    • "Of note, NKCC1 is also known to promote water transport across cell membranes [51]. Studies performed on cultured pigmented epithelial cells from the ciliary body of the fetal human eye transfected with NKCC1 reveal that NKCC1 works both as a water channel allowing passive water flux and as a water pump that transports water across apical membranes regardless of osmotic gradients [63]. Recent studies have demonstrated that NKCC1 transports 500 water molecules for each cycle of cation-chloride transport [64], which is comparable to that of aquaporins. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Na(+):K(+):2Cl(-) cotransporter 1 (NKCC1) has been implicated in mediating ischemia-, trauma- or ammonia-induced astrocyte swelling/brain edema in mammals. This study aimed to determine the effects of ammonia or terrestrial exposure on ammonia concentrations in the plasma and brain, and the mRNA expression and protein abundance of nkcc/Nkcc in the brain, of the swamp eel Monopterusalbus. Ammonia exposure led to a greater increase in the ammonia concentration in the brain of M. albus than terrestrial exposure. The brain ammonia concentration of M. albus reached 4.5 µmol g(-1) and 2.7 µmol g(-1) after 6 days of exposure to 50 mmol l(-1) NH4Cl and terrestrial conditions, respectively. The full cDNA coding sequence of nkcc1b from M. albus brain comprised 3276 bp and coded for 1092 amino acids with an estimated molecular mass of 119.6 kDa. A molecular characterization indicated that it could be activated through phosphorylation and/or glycosylation by osmotic and/or oxidative stresses. Ammonia exposure for 1 day or 6 days led to significant decreases in the nkcc1b mRNA expression and Nkcc1b protein abundance in the brain of M. albus. In comparison, a significant decrease in nkcc1b mRNA expression was observed in the brain of M. albus only after 6 days of terrestrial exposure, but both 1 day and 6 days of terrestrial exposure resulted in significant decreases in the protein abundance of Nkcc1b. These results are novel because it has been established in mammals that ammonia up-regulates NKCC1 expression in astrocytes and NKCC1 plays an important role in ammonia-induced astrocyte swelling and brain edema. By contrast, our results indicate for the first time that M. albus is able to down-regulate the mRNA and protein expression of nkcc1b/Nkcc1b in the brain when confronted with ammonia toxicity, which could be one of the contributing factors to its extraordinarily high brain ammonia tolerance.
    PLoS ONE 09/2013; 8(9):e69512. DOI:10.1371/journal.pone.0069512 · 3.23 Impact Factor
  • Source
    • "At non-elevated extracellular K+ concentration β1-adrenergic stimulation enhances regulatory volume increase in mouse astrocytes during hypertonic stimulation, again via a glycogenolytic effect (Xu, Song, Du, Yan, Hertz and Peng, unpublished results). The β1-adrenergic stimulation of volume increase relies on Na+,K+-ATPase-dependent stimulation of a combined uptake of H2O, Na+, K+ and 2Cl−, mediated by the co-transporter NKCC1 (Hamann et al., 2010). In brain slices extracellular hypertonicity reduces excitatory activity (Huang and Somjen, 1997), an effect similar to that of slow neuronal afterhyperpolarization (sAHP). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The involvement of glycogenolysis, occurring in astrocytes but not in neurons, in learning is undisputed (Duran et al., 2013). According to one school of thought the role of astrocytes for learning is restricted to supply of substrate for neuronal oxidative metabolism. The present "perspective" suggests a more comprehensive and complex role, made possible by lack of glycogen degradation, unless specifically induced by either (1) activation of astrocytic receptors, perhaps especially β-adrenergic or (2) even small increases in extracellular K(+) concentration above its normal resting level. It discusses (1) the known importance of glycogenolysis for glutamate formation, requiring pyruvate carboxylation; (2) the established role of K(+)-stimulated glycogenolysis for K(+) uptake in cultured astrocytes, which probably indicates that astrocytes are an integral part of cellular K(+) homeostasis in the brain in vivo; and (3) the plausible role of transmitter-induced glycogenolysis, stimulating Na(+),K(+)-ATPase/NKCC1 activity and thereby contributing both to the post-excitatory undershoot in extracellular K(+) concentration and the memory-enhancing effect of transmitter-mediated reduction of slow neuronal afterhyperpolarization (sAHP).
    Frontiers in Integrative Neuroscience 04/2013; 7:20. DOI:10.3389/fnint.2013.00020
  • Source
    • "There is evidence that water can be transported even against osmotic gradients (Zeuthen, 2010) by coupling its movements to the transport of a substrate that energizes its uphill transport. Likely molecules for such a mechanism are the Na + /K + /2Cl – cotransporter NKCC1 (Hamann et al., 2010) and some K + /Cl – cotransporters (Zeuthen, 2010). The activity of the basolaterally localized NKCC1 of alveolar epithelial cells could mediate the uptake of water into the epithelial cells, a hypothesis that needs to be tested. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The ability to breathe air represents a fundamental step in vertebrate evolution that was accompanied by several anatomical and physiological adaptations. The morphology of the air-blood barrier is highly conserved within air-breathing vertebrates. It is formed by three different plies, which are represented by the alveolar epithelium, the basal lamina, and the endothelial layer. Besides these conserved morphological elements, another common feature of vertebrate lungs is that they contain a certain amount of fluid that covers the alveolar epithelium. The volume and composition of the alveolar fluid is regulated by transepithelial ion transport mechanisms expressed in alveolar epithelial cells. These transport mechanisms have been reviewed extensively. Therefore, the present review focuses on the properties and functional significance of the alveolar fluid. How does the fluid enter the alveoli? What is the fate of the fluid in the alveoli? What is the function of the alveolar fluid in the lungs? The review highlights the importance of the alveolar fluid, its volume and its composition. Maintenance of the fluid volume and composition within certain limits is critical to facilitate gas exchange. We propose that the alveolar fluid is an essential element of the air-blood barrier. Therefore, it is appropriate to refer to this barrier as being formed by four plies, namely (1) the thin fluid layer covering the apical membrane of the epithelial cells, (2) the epithelial cell layer, (3) the basal membrane, and (4) the endothelial cells.
    Frontiers in Physiology 05/2012; 3:146. DOI:10.3389/fphys.2012.00146 · 3.53 Impact Factor
Show more