MINERAL FIBER-INDUCED LEUKOCYTE ACTIVATION - THE ROLE OF INTRACELLULAR AND EXTRACELLULAR CALCIUM

The role of intra- and extracellular calcium in the activation of huma n polymorphonuclear leukocytes (PMNL) to produce reactive oxygen metab olites (ROM) were studied by using soluble, formyl-methionyl-leucyl-ph enylalanine (fMLP) or phorbol myristate acetate (PMA), or particulate stimuli, quartz or chrysotile. A calcium channel inhibitor, verapamil, attenuated only quartz-induced elevation of free intracellular calciu m ([Ca2+](i)) and ROM production. Likewise, ethyleneglycol-bis (aminoe thyl ether) tetraacetic acid (EGTA) attenuated quartz-, chrysotile- an d fMLP-induced elevation of [Ca2+](i) and ROM production. It also inhi bited PMA-induced ROM production. A calcium ionophore, A23187 amplifie d ROM production by all of these stimuli. These results suggest that b oth intra- and extracellular calcium are required for the full activat ion of respiratory burst by soluble and particulate stimuli in human P MNL.