Release of adenosine and its metabolites from activated human leucocytes

Abstract

Human leucocytes whose adenine nucleotide pool was prelabelled with [3H]adenine were investigated for their capacity to release adenosine and its metabolites and histamine when activated with the calcium ionophore A23187, anti-immunoglobulin E and the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (f-MLP). Sixty-nine per cent of the 3H-label assimilated by the cells was incorporated into their adenine nucleotide pool in the ratio adenosine 5'-phosphate (AMP):adenosine 5'-pyrophosphate (ADP):adenosine 5'-triphosphate (ATP), 3:1:1. Spontaneous release of label from leucocytes plateaued at 5 min at 22.1 +/- 4.2% of the total radiolabel incorporated and mainly consisted of hypoxanthine, inosine and adenosine. Activation of cells with the calcium ionophore A23187 (1.0 mumol/l) caused a net increase in [3H]purine release above baseline of 27.9 +/- 4.6% accompanied by a net basophil histamine release of 46.6 +/- 9.4%. A23187 (1.0-3.0 mumol/l) caused a parallel concentration-dependent release of labelled purines and histamine. Purified mononuclear cells and granulocytes exhibited a similar ionophore-dependent capacity to release [3H]purines. The distribution of label did not significantly differ between supernatants of activated and non-activated cells. Preincubation of cells with dipyridamole (10 mumol/l) and erythro-9-(2-hydroxy-3)-nonyladenine (EHNA) (10 mumol/l) to inhibit uptake and catabolism of adenosine respectively, produced an increase in adenosine at the expense of hypoxanthine recovered from the supernatant of both ionophore-stimulated and resting cells. Activation of leucocytes with f-MLP (1.0 mumol/l) caused a net increase in release of basophil histamine, but was associated with only a transient net increase in release of [3H]purine in four of five experiments.(ABSTRACT TRUNCATED AT 250 WORDS)