Prolactin induces calcium influx and release from intracellular pools in human T lymphocytes by activation of tyrosine kinases

The early events related to intracellular signals after prolactin (PRL) act ivation in T lymphocytes are not clearly established. The aim of this work was to study the effect of PRL in cytosolic calcium levels in human T lymph ocytes. By using the dye FURA-2 AM, the variations in cytosolic Ca2+ were s tudied in peripheral human T lymphocytes isolated from extracted blood from healthy donors. Fifty nanograms per milliliter PRL induces a small increas e in cytosolic calcium. When the cells are preincubated overnight (16-20 h) in the presence of PRL, the increase in calcium is higher. This high incre ase is due to the release from intracellular pools and to the influx from t he extracellular media. That is, after overnight incubation with PRL, calci um influx in T cells follows the capacitative model. Since PRL receptor (PR -L-R) activation involves the tyrosine kinase pathway, we check calcium eff ect in the presence of genistein, a known inhibitor of tyrosine kinases. Wh en cells are preincubated in the presence of 10 muM genistein, and PRL is i mmediately added, no increase in cytosolic calcium is observed. The presenc e of genistein also completely blocks the increase in cytosolic calcium sti mulated by PRL after overnight incubation with PRL. In the presence of PRL and N,N-dimethyl-D-erythro-sphingosine (DMS), a stimulus that increases cyt osolic calcium in T cells by tyrosine kinase stimulation, a high, even insi gnificant, calcium influx is induced. However, when the cells are incubated overnight in the presence of PRL, and then DMS is added, a significant inc rease in cytosolic calcium levels takes place. This increase is associated with an increase in calcium release from intracellular pools and an increas e in calcium uptake. Genistein reduces the influx of external calcium induc ed by DMS after short incubation with PRL and significantly inhibits both, calcium pools empty, and calcium influx is induced by DMS after overnight i ncubation with PRL. In summary, PRL induces calcium influx in normal T lymp hocytes. The influx is magnified after long PRL exposures, intracellular Ca 2+ pool-dependent, and activated through tyrosine kinases. (C) 2001 Elsevie r Science Inc. All rights reserved.