AGONIST-STIMULATED CL- EFFLUX FROM HUMAN NEUTROPHILS - A COMMON PHENOMENON DURING NEUTROPHIL ACTIVATION

When human peripheral blood neutrophils were stimulated with various a gonists which activate and/or prime neutrophils, we found that Cl- eff lux was enhanced with a dramatic (50%) loss of intracellular Cl-. Inte restingly, the Cl- efflux was enhanced by both agonists which induce a rapid transient increase in intracellular Ca2+ concentration ([Ca2+]i ) [class I, e.g. N-formyl-methionyl-leucyl-phenylalanine (fMLP), inter leukin-8 (IL8), platelet-activating factor, leukotriene B4 and C5a] an d those which do not induce such an [Ca2+]i elevation [class II, e.g. tumor necrosis factor alpha (TNF) and granulocyte-macrophage colony-st imulating factor (GM-CSF)]. The time course of agonist-stimulated Cl- efflux differed depending on the agonist. Class I agonists such as IL8 and fMLP exhibited a 1 min lag phase before the onset of Cl- efflux; class II agonists such as GM-CSF and TNF displayed a 2 and 5 min lag p hase, respectively. Both IL8 (class I)- and TNF (class II)-stimulated Cl- efflux exhibited similar sensitivity to inhibition by different ty pes of ion transport inhibitors [ethacrynic acid (EA), amiloride, etam ido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid, anthracene-9-carb oxylic acid, and 4-4'-diisothiocyanatostilbene-2,2'-disulfonic acid]. On the other hand, natural Cl- efflux, which is thought to be mainly m ediated by Cl-/Cl- self exchange, was not inhibited by EA (0.5 mM) or amiloride (0.3 mM). These results imply that both class I and class II agonist-stimulated Cl- efflux occurs via a common Cl- transporter whi ch is different from that reported previously in resting human neutrop hils. Although all agonists which induced a Cl- efflux also induced sh ape change of neutrophils, there did not appear to be a causal relatio nship between shape change and agonist-stimulated Cl- efflux. However, a temporal correlation was found to exist between agonist-stimulated Cl- efflux and intracellular alkalinization following agonist stimulat ion. Agonist-stimulated Cl- efflux therefore seems to be a common phen omenon activated by several agonists which act through different signa l transduction pathways.