The ATP4- receptor-operated ion channel of human lymphocytes : inhibition of ion fluxes by amiloride analogs and by extracellular sodium ions

• Published in: Archives of biochemistry and biophysics Vol. 292; no. 2; pp. 411 - 418
• Main Authors: WILEY, J. S, RONG CHEN, WILEY, M. J, JAMIESON, G. P
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier 01.02.1992
• Subjects: Adenosine - pharmacology; Adenosine Triphosphate - pharmacology; Amiloride - analogs & derivatives; Amiloride - pharmacology; Biological and medical sciences; Calcium - blood; Cell Membrane Permeability - drug effects; Cytosol - drug effects; Cytosol - metabolism; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Immunobiology; In Vitro Techniques; Ion Channels - drug effects; Ion Channels - metabolism; Kinetics; Leukemia, Lymphocytic, Chronic, B-Cell - blood; Lymphocytes - drug effects; Lymphocytes - metabolism; Lymphoid cells: ontogeny, maturation, markers, receptors, circulation and recirculation; Ribonucleotides - pharmacology; Rubidium - blood; Sodium - pharmacology; Human; Flow cytometry; Calcium; Leukemia; Ionic channel; ATP; Lymphocyte; Dose activity relation; Biological receptor
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/0003-9861(92)90010-t

Extracellular ATP is known to increase the membrane permeability of a variety of cells. Addition of ATP to human leukemic lymphocytes loaded with the Ca2+ indicator, fura-2, induced a rise in cytosolic Ca2+ concentration which was attenuated or absent in NaCl media compared with KCl, choline Cl, or NMG Cl media. In contrast, anti-immunoglobulin antibody gave similar Ca2+ transients in NaCl and KCl media. A half-maximal inhibition of peak ATP-induced Ca2+ response was observed at 10-16 mM extracellular Na+. Basal 45Ca2+ influx into lymphocytes was stimulated 9.6-fold by ATP added to cells in KCl media, but the effect of ATP was greatly reduced for cells in NaCl media. Hexamethylene amiloride blocked 74% of the ATP-stimulated Ca45 uptake of cells in KCl media. Flow cytometry measurements of fluo-3-loaded cells confirmed that the ATP-induced rise in cytosolic Ca2+ was inhibited either by extracellular Na+ or by addition of hexamethylene amiloride. Extracellular ATP stimulated 86Rb efflux from lymphocytes 10-fold and this increment was inhibited by the amiloride analogs in a rank order of potency 5-(N-methyl-N-isobutyl)amiloride greater than 5-(N,N-hexamethylene)amiloride greater than 5-(N-ethyl-N-isopropyl)amiloride greater than amiloride. ATP-induced 86Rb efflux showed a sigmoid dependence on the concentration of ATP and Hill analysis gave K1/2 of 90 and 130 microM and n values of 2.5 and 2.5 for KCl and NaCl media, respectively. However, the maximal ATP-induced 86Rb efflux was 3-fold greater in KCl than in NaCl media. Raising extracellular Na+ from 10 to 100 mM increased ATP-induced Na+ influx from a mean of 2.0 to 3.7 nEq/10(7) cells/min, suggesting either saturability or self-inhibition by Na+ of its own influx. These data suggest that ATP opens a receptor-operated ion channel which allows increased Ca2+ and Na+ influx and Rb+ efflux and these fluxes are inhibited by extracellular Na+ ions as well as by the amiloride analogs.