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10th International Congress "Cell Volume Regulation: Novel Therapeutic Targets and Pharmacological Approaches"
TRPM2-AC IS THE HYPERTONICITY-INDUCED CATION CHANNEL (HICC) IN HELA CELLS AND THE ECTO-ENZYME CD38 IS A MEDIATOR OF ITS ACTIVATION
Numata, T.v, Sato, K.1, Christmann, J.3, Marx, R.3, Mori, Y.2, Okada, Y.1, and Wehner, F.1'3
1 Department of Cell Physiology, National Institute of Physiological Sciences, Okazaki, Japan
2 Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto Japan
3 Department of Systemic Cell Biology, Max-Planck-Institute of Molecular Physiology, Dortmund, Germany
Hypertonicity-induced cation channels (HICCs) are key-players in proliferation and apoptosis but their molecular correlate remains obscure. Also, the activation pattern of HICCs was not defined yet. We report that in HeLa cells, intracellular adenosine diphosphate ribose (ADPr) and cyclic ADPr, as activators of TRPM2, elicit cation currents that are identical to the osmotic activation of HICCs. Silencing of TRPM2 and of the ecto-enzyme CD38 (as the supposed source of ADPr and cADPr) inhibit HICC- and nu-cleotide-induced currents as well as the osmotic volume response of cells. Quantification of intracellular cADPr and
extracellular application of nucleotides reveal, however, that it is the outwardly directed gradient rather than the intracel-lular activity of ADPr and cADPr triggering TRPM2 and, very likely, this export goes together with a biotransformation of nucleotides. Cloning of TRPM2 identifies the AC-splice variant as molecular correlate of the HICC, which is supported by quantification of its Ca2+ selectivity. Finally, pull-down and FRET/FLIM experiments reveal a close proximity of TRPM2 and CD38 and we propose a transport related nucleotide export via CD38 as novel mechanism of TRPM2 activation.
AN EMERGING CONCEPT OF VASCULAR SALT SENSITIVITY IN MAN
Oberleithner, H.
Institute of Physiology II, University of Münster, Germany
For millions of years, daily sodium chloride intake in man was about 1g. Then recently, about 10,000 years ago, salt intake increased by about ten-fold because of the practice of using salt as a food preservative. If salt intake exceeds the kidneys' ability for salt excretion, then salt is deposited in the body which affects heart, blood vessels and kidneys. In this context, the endothelial surface layer facing the blood stream became a focus of interest. This soft layer, termed endothelial glycocalyx, is a negatively charged biopolymer known to preferentially bind sodium. After a salty meal, the translocation of sodium from the blood into the interstitium is delayed by the significant buffering capacity of the endothelial glycocalyx. Excessive sodium intake over long periods damages the glycocalyx and leads to a decrease in its sodium buffering capacity. It has been shown recently that, after mechanical interaction of blood with a damaged endothelial glycocalyx, erythrocyte surfaces also become damaged [1]. This observation led to the conclusion that vascular sodium buffer capacity of an individual could be derived from a blood sample. A test system (Salt-Blood-Test; SBT) was developed
based upon the sodium-dependent erythrocyte zeta-potential [2]. Erythrocyte sedimentation velocity was measured in isosmotic, biopolymer-supplemented electrolyte solutions of different sodium concentrations. Erythro-cyte sodium sensitivity (ESS), inversely related to eryth-rocyte sodium buffer capacity, was expressed as the ratio of the erythrocyte sedimentation velocities of 150 over 125 mM Na+ solutions (ESS = 150Na+/125Na+). In 61 healthy individuals (mean age: (23.0 ± 0.5) years) ESS ranged between 2 and 8. The mean value was 4.30 ± 0.19. In conclusion, the SBT could serve as an in vitro test system for the evaluation of salt sensitivity allowing follow-up measurements in the prevention and treatment of vascular dysfunctions.
References
1. Oberleithner, H. (2013). Vascular endothelium leaves fingerprints on the surface of erythrocytes. Pflugers Arch doi 10.1007/s00424-013-1288-y
2. Oberleithner, H. and Wilhelmi, M. (2013). Determination of erythrocyte sodium sensitivity in man. Pflugers Arch doi 10.1007/s00424-013-1289-y
Бюллетень сибирской медицины, 2013, том 12, № 4, с. 24-68
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