The increase in intracellular free Ca2+ ([Ca2+](i)) associated with interaction of monocyte chemotactic protein-1 (MCP-1) and related chemokines beta with adherent human blood monocytes was investigated at the single-cell level, We used f-MLP as reference chemotactic agent, MCP-1 caused an increase in [Ca2+](i) in individual adherent monocytes, with 95% of cells responding to the chemokine at 20 ng/mL, Response to MCP-1 was already detectable at 1 pg/mL, whereas at least 5 ng/mL were required for significant chemotactic response. The kinetics of the increase in [Ca2+](i) were considerably different for MCP-1 compared with f-MLP. MCP-1 produced a slow increase of [Ca2+](i) that reached a plateau in 5 to 7 minutes. On the other hand, the increase of [Ca2+](i) induced by f-MLP appeared to be biphasic, with a fast phase peaking after 5 to 40 seconds followed by a slower wave. Blocking of Ca2+ channels by Ni2+ or Cd2+ and/or chelation of extracellular free Ca2+ considerably reduced but did not abolish response to MCP-1, had no effect on the first wave of [Ca2+](i) induced by f-MLP, and completely abrogated the second, slower wave, Thapsigargin, which empties intracellular Ca2+ stores, inhibited f-MLP-induced [Ca2+](i) increase but fully blocked the action of MCP-1 only when combined with Ni2+. Thus, increase of [Ca2+](i) induced by MCP-1 is apparently due to independent opening of a channel and mobilization from intracellular stores, whereas f-MLP-induced mobilization of Ca2+ from stores causes subsequent opening of a channel. At variance with MCP-1, the related chemokine MCP-2 induced only a low increase of [Ca2+](i) in about 40% of adherent monocytes. Inhibition of chemokine-induced increase of [Ca2+](i) by cholera or pertussis toxin indicated that MCP-1 and MCP-2 activate monocytes through different intracellular pathways. These results demonstrate at the single-cell level that the mechanisms and dynamics of increased [Ca2+](i) are considerably different for f-MLP and chemokines beta. In addition, the [Ca2+](i) increase induced by the two related chemokines beta MCP-1 and MCP-2 appears to be differently regulated, suggesting interaction with distinct receptors. (C) 1995 by The American Society of Hematology.
