Extracellular ATP stimulates an amiloride-sensitive sodium influx in human lymphocytes.
Extracellular ATP has been shown to increase the Na+ permeability of human lymphocytes by 3 to 12-fold. The kinetics of this ATP-induced response were studied by measuring 22Na+ influx into chronic lymphocytic leukemic lymphocytes incubated in low-sodium media without divalent cations. ATP-stimulated uptake of 22Na-ions was linear over 4 min incubation and this influx component showed a sigmoid dependence on ATP concentration. Hill analysis yielded a K1/2 of 160 microM and a n value of 2.5. The nucleotide ATP-gamma-S (1-2 mM) gave 30% of the permeability increase produced by ATP, but UTP (2 mM) and dTTP (2 mM) had no effect on 22Na influx. The amiloride analogs 5-(N-ethyl-N-isopropyl) amiloride and 5-(N,N-hexamethylene) amiloride, which are potent inhibitors of Na(+)-H+ countertransport, abolished 72-95% of the ATP-stimulated 22Na+ influx. However, the involvement of Na(+)-H+ countertransport in the ATP-stimulated Na+ influx was excluded by three lines of evidence. Sodium influx was stimulated 7-fold by extracellular ATP but only 2.4-fold by hypertonic conditions which are known to activate Na(+)-H+ countertransport. Addition of ATP to lymphocytes produced no change in intracellular pH when these cells were suspended in isotonic NaCl media. Finally ATP caused a membrane depolarization of lymphocytes which is inconsistent with stimulation of electroneutral Na(+)-H+ exchange. These data suggest that ATP acts cooperatively to induce the formation of membrane channels which allow increased Na+ influx by a pathway which is partially inhibited by amiloride and its analogs.
Wiley
J S
JS
Haematology Department, Austin Hospital, Heidelberg, Australia.
Jamieson
G P
GP
Mayger
W
W
Cragoe
E J
EJ
Jopson
M
M
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism; D008214:Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D012964:Sodium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013942:Thymine Nucleotides / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology
D013942:Thymine Nucleotides; C057360:5-(N,N-hexamethylene)amiloride; D000584:Amiloride; D000255:Adenosine Triphosphate; D012964:Sodium; C024157:thymidine 5'-triphosphate; D014544:Uridine Triphosphate; C039614:ethylisopropylamiloride