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10th International Congress "Cell Volume Regulation: Novel Therapeutic Targets and Pharmacological Approaches"
NA+-K+-2CL- COTRANSPORTER IN CEREBRAL ISCHEMIA Sun, D
University of Pittsburgh, Pittsburgh, USA
Na+-K+-2Cl- cotransporter isoform 1 (NKCC1) transports 1Na+, 1K+, and 2Cl- ions into cells and is important in regulation of intracellular Na+ and Cl-, cell volume, and K+ uptake in the central nervous system under physiological conditions. Under ischemic conditions, NKCC1 activation causes intracellular Na+ and Cl- overload in astro-cytes and neurons. The intracellular Na+ overload subsequently stimulates the reverse mode operation of Na+/Ca2+ exchange and leads to a delayed, secondary cytosolic Ca2+
rise and Ca2+ dysregulation in ER and mitochondria. Most importantly, either pharmacological inhibition or genetic ablation of NKCC1 shows significant neuroprotective effects in in vivo focal ischemia model and in vitro ischemia model. Thus, over-stimulation of NKCC1 activity contributes to cerebral ischemic damage. Better understanding of NKCC1 regulation and function will benefit for developing more effective stroke therapy.
FACE MODULATES TRANSEPITHELIAL WATER RESORPTION IN THE ALVEOLUS
Thompson, K.1, Korbmacher, J.1, Hobi, N.1, Hecht, E.1, Wittekindt, O.1, Miklavc, P.1, Kranz, C.2, Dietl, P.1, and Frick, M.1
1 Institute of General Physiology, University of Ulm, Germany
2 Insitute of Analytical and Bioanalytical Chemistry, University of Ulm, Germany
Tight regulation of the alveolar fluid layer is essential for lung function. Impaired water transport across lung epithelia results in severe health problems ranging from impairment of mucociliary clearance to edema. Yet, the mechanisms and the role of alveolar epithelial cells for maintaining alveolar fluid homeostasis are still controversial. We have recently described that exocytosis of lamellar bodies (LBs) in primary alveolar type II (ATII) epithelial cells results in "fusion-activated cation-entry" (FACE) via P2X4 receptors on LBs. Fusion of LBs with the apical plasma membrane (PM) and subsequent cation entry via P2X4 receptors offers a new potential route for apical to basolateral water movement in the alveolus.
Initially, we looked at the Isc of ATII cell monolayers, and the role for agonist induced activation of P2X4 following LB fusion. While both ATP and UTP can stimulate fusion of LBs with the PM, only ATP can activate FACE. While stimulation with both resulted in an increase in Isc and fusion, an additional increase in Isc, indicating FACE, was only seen when an initial stimulation via UTP was
followed by ATP. Over-expressing dominant-negative P2X4 abrogated this effect by ~50%, whereas potentiating P2X4 lead to ~80% increase in Isc. Using fluorescently labeled dextran loaded apically on ATII cell monolayers grown at air-liquid interphase, we were able to directly establish a role for P2X4 receptors in water transport from the alveolar surface fluid (ASF) across the alveolar epithelium. Fluid transport was seen only in the event of LB fusions that were followed by FACE. Again, monolayers transfected with dominant-negative P2X4 reduced the water resportion from the ASF.
Finally, the link between these two studies of cation movement via the P2X4 receptor and water transport in the whole lung was studied in in situ experiments looking at changes in lung compliance upon activation of FACE at time of LB fusion. Results from the in situ experiments confirmed the idea that FACE directly couples surfactant secretion and transepithelial water transport in the lung.
Бюллетень сибирской медицины, 2013, том 12, № 4, с. 24-68
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