The P2Z-purinoceptor of human lymphocytes: actions of nucleotide agonists and irreversible inhibition by oxidized ATP.
1. Extracellular adenosine triphosphate (ATP) is known to open a receptor-operated ion channel (P2Z class) in human lymphocytes which conducts a range of cationic permeants. The activity of a range of different agonists and inhibitors towards the P2Z-purinoceptor was investigated by measuring the agonist-induced influx of Ba2+ into fura-2 loaded lymphocytes. 2. The most potent agonist was 2' & 3'-0-(4-benzoylbenzoyl)-ATP (benzoylbenzoic ATP) which gave 2 fold greater maximum Ba2+ influx and had a 10 fold lower EC50 than for ATP. The rank order of agonist potency in K(+)-media was benzoylbenzoic ATP >> ATP = 2-methylthio ATP = 2-chloro ATP > ATP-gamma-S. ADP, UTP and alpha,beta-methylene ATP were unable to stimulate Ba2+ influx. 3. Extracellular Na+ inhibited the increment of Ba2+ influx induced by all concentrations of ATP, 2-methylthio ATP, 2-chloroATP and ATP-gamma-S. This inhibitory effect of extracellular Na+ is also reflected in the different EC50s for benzoylbenzoic ATP (8 microM in K(+)-media, 18 microM in Na(+)-media) but the maximal response to this agonist was the same in the presence or absence of Na+. 4. Treatment of lymphocytes with 2,3 dialdehyde ATP (oxidized ATP0 at 300 microM for 60 min gave total and irreversible inhibition of ATP-induced Ba2+ influx. 5'-p-Fluorosulphonyl benzoyladenosine (FSBA) also was an irreversible inhibitor but the maximal inhibition achieved was 90%. 5. It is concluded that the P2z-purinoceptor of human lymphocytes has a rank order of agonist potency which clearly distinguishes it from other P2-receptors and that oxidized ATP is a convenient irreversible inhibitor for the P2Z-purinoceptor.
Wiley
J S
JS
Haematology Department, Austin Hospital, Heidelberg, Victoria, Australia.
Chen
J R
JR
Snook
M B
MB
Jamieson
G P
GP
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003470:Culture Media; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005470:Fluorometry; D006801:Humans; D066298:In Vitro Techniques; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction; D011188:Potassium / Q000494:pharmacology; D011685:Purine Nucleotides / Q000494:pharmacology*; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D012964:Sodium / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D003470:Culture Media; D011685:Purine Nucleotides; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D001464:Barium; D000255:Adenosine Triphosphate; D012964:Sodium; D011188:Potassium; D002118:Calcium