The ATP4- receptor-operated channel (P2Z class) of human lymphocytes allows Ba2+ and ethidium+ uptake: inhibition of fluxes by suramin.
It is now recognized that extracellular ATP can open a receptor-operated ion channel in a variety of cell types. In human lymphocytes this P2Z purinergic channel conducts Na+, K+, Rb+, Li+, and Ca2+ but its permeability to larger cations is not known. Fluorometric measurements were used to show that ATP4- induced the entry of Sr2+ (87 Da) and Ba2+ (137 Da) into human lymphocytes loaded with fura-2. Flow cytometry was used to show that ATP4- induced the entry of ethidium+ (314 Da) but that the larger propidium2+ cation (414 Da) was excluded. ATP(4-)-induced entry of both Ba2+ and ethidium+ showed features previously demonstrated for smaller cation permeants: (i) inhibition by amiloride analogs, (ii) sigmoid dependence of flux on ATP concentrations, and (iii) inhibition by extracellular Na+ ions. Specific inhibitors of L-type voltage-gated Ca2+ channels (nisoldipine and diltiazem) had no effect on ATP(4-)-induced Ba2+ influx. Suramin and reactive blue 2, which are recognized antagonists of ATP-operated purinergic receptors in other tissues, inhibited ATP-induced uptake of ethidium+ in lymphocytes with K1/2 of 61 and 69 microM, respectively. However, hexamethylene amiloride was a more potent inhibitor of ATP-induced ethidium+ uptake with a K1/2 of 13 microM. These data show that the ATP4- receptor-operated channel of human lymphocytes allows influx of cations as large as Ba2+ or ethidium+ and that this influx is inhibited by suramin and reactive blue 2.
Wiley
J S
JS
Haematology Department, Austin Hospital, Heidelberg, Victoria, Australia.
Chen
R
R
Jamieson
G P
GP
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D001464:Barium / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D004996:Ethidium / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D015451:Leukemia, Lymphocytic, Chronic, B-Cell; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D011419:Propidium / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D013324:Strontium / Q000378:metabolism; D013498:Suramin / Q000494:pharmacology*; D014227:Triazines / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D007473:Ion Channels; D011500:Protein Synthesis Inhibitors; D014227:Triazines; D001464:Barium; D011419:Propidium; C012842:Cibacron Blue F 3GA; D013498:Suramin; D000255:Adenosine Triphosphate; D014700:Verapamil; D004996:Ethidium; D002118:Calcium; D013324:Strontium