Complex regulation of human neutrophil activation by actin filaments: Dihydrocytochalasin B and botulinum C2 toxin uncover the existence of multiple cation entry pathways

In human neutrophils, the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenalalanine - (fMLP), the Ca2+-ATPase inhibitor, thapsigargin, and the lectins, concanavalin A (Con A) and mistletoe lectin I (ML I), stimulate the entry of Ca2+ and Na+ with subsequent activation of exocytosis and superoxide anion (O-2(-)) formation, We studied the role of actin in neutrophil activation, The actin filament-disrupting substances, dihydrocytochalasin B (dhCB) and botulinum C2 toxin (C2 toxin) potentiated fMLP- and lectin-stimulated Ca2+- and Na+ entry, Lectin-induced Mn2+ entry was enhanced by actin disruption, whereas fMLP-triggered Mn2+ entry was unaffected, dhCB and C2 toxin inhibited fMLP- and lectin-stimulated Ba2+ influx, The actin disrupters also inhibited fMLP- and ML I-induced Sr2+ influx, whereas Con A-stimulated Sr2+ entry was not influenced by dhCB and C2 toxin. Thapsigargin-stimulate d cation entry was not altered by actin disruption, DhCB and botulinum C2 toxin potentiated lysozyme release induced by all four stimuli, Con A and ML I per se activated O-2(-) formation only in the presence and not in the absence of dhCB, Con A potentiated the stimulatory effects of ML I on O-2(-) formation in the presence of dhCB and primed neutrophils to respond to ML I in the absence of dhCB. Our data indicate the following: (1) dhCB and C2 toxin uncover the existence of multiple cation entry pathways in neutrophils; (2) actin disruption facilitates exocytosis and O-2(-) formation by enhancement of Ca2+- and Na+ entry and by altering the function of proteins involved in activation of secretion and O-2- formation; and (3) Con A and ML I, which possess different sugar specificities, activate different signaling pathways in neutrophils.