POLYMORPHONUCLEAR LEUKOCYTES FROM ASTHMATICS RELEASE MORE CALCIUM FROM INTRACELLULAR STORES AND HAVE ENHANCED CALCIUM INCREASE AFTER STIMULATION WITH N-FORMYL-METHIONYL-LEUCYL-PHENYLALANINE

Polymorphonuclear leukocytes isolated from peripheral blood of asthmat ics appear to be primed to release more reactive oxygen species than c ells of healthy subjects. The enhanced agonist-induced rise in the int racellular free calcium concentration may be responsible for this incr eased respiratory burst. To test this hypothesis we studied the N-form yl-methionyl-leucyl-phenylalanine- and cyclopiazonic acid -(an inhibit or of Ca2+-ATPase of intracellular calcium stores) induced calcium inc rease in the polymorphonuclear leukocytes of 28 subjects (16 with mode rate asthma, 69.6%+/-8.3% predicted normal peak expiratory flow and 12 normal controls) using a fluorescent probe Fura-2AM at 100 nM and 1 m M extracellular calcium concentrations. In 1 mM calcium, the N-formyl- methionyl-leucyl-phenylalanine-induced calcium increase was 1.7-fold h igher in asthmatics than in healthy subjects. Similarly, the contribut ion of calcium from intracellular stores to the calcium response to N- formyl-methionyl-leucyl-phenylalanine was higher in asthmatics (55% +/ - 14% vs. 39%+/-14%, P<0.01). The pool of calcium released from intrac ellular stores by N-formyl-methionyl-leucyl-phenylalanine and cyclopia zonic acid was 2.3- and 2.2-fold larger than in control cells. There w as a correlation between maximal intracellular calcium concentration r elated to N-formyl-methionyl-leucyl-phenylalanine-induced calcium rele ase from intracellular stores and forced expiratory volume in 1 s expr essed as percentage predicted and reversibility in asthmatics (r=0.63, r= -0.53, P < 0.05). In conclusion, polymorphonuclear leukocytes of a sthmatics exhibit an altered calcium response that is mainly dependent on increased calcium release from intracellular stores.