The role of the cytosolic free Ca2+ transient for fMet-Leu-Phe induced actin polymerization in human neutrophils.
We have addressed the important question as to if and how the cytosolic free Ca2+ concentration, [Ca2+]i, is involved in fMet-Leu-Phe induced actin polymerization in human neutrophils. Stimulation of human neutrophils with the chemotactic peptide (10(-7) M), known to result in a prompt rise of the [Ca2+]i to above 500 nM, also induced a rapid decrease of monomeric actin, G-actin, content (to 35% of basal) and increase of filamentous actin, F-actin, content (to 320% of basal). A reduction of the fMet-Leu-Phe induced [Ca2+]i transient to about 250 nM, resulted in a less pronounced decrease of G-actin content (to 80% of basal) and increase of F-actin content (to 235% of basal). A total abolishment of the chemotactic peptide induced [Ca2+]i rise, still led to a decrease of the G-actin content (to 85% of basal) and increase of F-actin (to 200% of basal). These results indicate that the [Ca2+]i rise is not an absolute requirement, but has a modulating role for the fMet-Leu-Phe induced actin polymerization. Another possible intracellular candidate for fMet-Leu-Phe induced actin polymerization is protein kinase C. However, direct activation of protein kinase C by phorbol 12-myristate 13-acetate (PMA) only resulted in a minor increase of F-actin content. The recent hypothesis that a metabolite of the polyphosphoinositide cycle, independently of [Ca2+]i and protein kinase C, is responsible for actin polymerization agrees well with these results and by the fact that preexposure to pertussis toxin totally abolished a subsequent increase of F-actin content induced by fMet-Leu-Phe.
D008841:Actin Cytoskeleton / Q000187:drug effects* / Q000502:physiology; D000199:Actins / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D002634:Chemotaxis, Leukocyte / Q000187:drug effects*; D003599:Cytoskeleton / Q000187:drug effects*; D006801:Humans; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000648:ultrastructure*; D037342:Pertussis Toxin; D011108:Polymers; D011493:Protein Kinase C / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000199:Actins; D011108:Polymers; D010566:Virulence Factors, Bordetella; D009240:N-Formylmethionine Leucyl-Phenylalanine; D037342:Pertussis Toxin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium