Publications & Reports

The ATP4- receptor-operated channel (P2Z class) of human lymphocytes allows Ba2+ and ethidium+ uptake: inhibition of fluxes by suramin.

J S Wiley, R Chen, G P Jamieson
Haematology Department, Austin Hospital, Heidelberg, Victoria, Australia.

Abstract

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.

Publication

  • Journal: Archives of Biochemistry and Biophysics
  • Published: 15/08/1993
  • Volume: 305
  • Issue: 1
  • Pagination: 54-60

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