Signal transduction events in stimulated rat neutrophils: Effects of adenine nucleotides

Abstract

When rat neutrophils were stimulated with chemotactic peptide (N-formyl-Met-Leu-Phe; fMLP), phorbol myristate acetate (PMA), or immune complexes in the presence of homologous platelets, responses were enhanced. Secretion products of thrombin-stimulated platelets as well as ATP, ATP[gamma]S, or ADP enhanced responses of fMLP-stimulated neutrophils, although these nucleotides did not, by themselves, initiate an response. Calcium transients were measured in neutrophils which were stimulated with fMLP under a variety of conditions (+/-ATP[gamma]S, +/-cytochalasin B) which enhance responses. Neutrophils incubated with ATP[gamma]S alone developed brief calcium transients similar to those produced by fMLP. As compared to changes in intracellular calcium in fMLP-stimulated neutrophils, the copresence of ATP[gamma]S with fMLP did not cause a statistically significant difference in the calcium transients, even though production was enhanced. In contrast, in the presence of cytochalasin B, the addition of ATP[gamma]S to fMLP-stimulated neutrophils produced greatly sustained and protracted elevations in intracellular calcium, correlating with further enhancement of responses. In fMLP-stimulated neutrophils the latter phases of the calcium transients appeared to be dependent in part on the availability of extracellular calcium. These data suggest that ATP[gamma]S-induced enhancement of responses in fMLP-stimulated rat neutrophils may be related to two mechanisms, one being independent of fMLP-induced intracellular calcium transients and the other, which is related to the presence of cytochalasin B, being linked to sustained elevations in intracellular calcium associated with mobilization of extracellular calcium.