Activation by chemotactic peptide of a receptor-operated Ca2+ entry pathway in differentiated HL60 cells

N-Formyl-methionyl-leucyl-phenylalanine (fMLP) is able to accelerate Ca2+ entry into differentiated HL60 cells by a rather indirect mechanism consisting of the opening of a plasma membrane pathway activated by the emptying of the intracellular Ca2+ stores caused by the agonist. This Ca2+ pathway can also be fully activated by Ca2+ store depletion with thapsigargin. We show here that, in addition to this store-operated Ca2+ entry pathway (SOCP), fMLP is able to activate another receptor-operated Ca2+ pathway in thapsigargin-treated HL60 cells differentiated for 24 h with dimethyl sulfoxide. Activation by fMLP was produced even in cells with fully empty Ca2+ stores. It started 30 s after fMLP addition, was maximal after 2 min and then disappeared within 5 min. This pathway was similar to SOCP in that it allowed passage of Mn2+ and Ba2+ and was antagonized by Ni2+ and by cytochrome P-450 inhibitors. fMLP is also able to inhibit SOCP by a mechanism involving protein phosphorylation. Both the fMLP-induced activation of Ca2+ entry and the inhibition of SOCP were prevented by pretreatment with pertussis toxin. However, the first appeared earlier than the last along differentiation of HL60 cells. This suggests that the inhibition of SOCP requires not only the development of fMLP receptors but also an additional component placed distally to the G protein in the transduction mechanism.