Polymorphonuclear leukocytes from asthmatics release more calcium from intracellular stores and have enhanced calcium increase after stimulation withN-formyl-methionyl-leucyl-phenylalanine
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Polymorphonuclear leukocytes isolated from peripheral blood of asthmatics appear to be primed to release more reactive oxygen species than cells of healthy subjects. The enhanced agonist-induced rise in the intracellular free calcium concentration may be responsible for this increased respiratory burst. To test this hypothesis we studied theN-formyl-methionyl-leucyl-phenylalanine- and cyclopiazonic acid-(an inhibitor of Ca2+-ATPase of intracellular calcium stores) induced calcium increase in the polymorphonuclear leukocytes of 28 subjects (16 with moderate 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 mM extracellular calcium concentrations. In 1 mM calcium, theN- formylmethionyl-leucyl-phenylalanine-induced calcium increase was 1.7-fold higher in asthmatics than in healthy subjects. Similarly, the contribution of calcium from intracellular stores to the calcium response toN-formyl-methionyl-leucyl-phenylalanine was higher in asthmatics (55% ±14% vs. 39%±14%, P<0.01). The pool of calcium released from intracellular stores byN-formyl-methionyl-leucyl-phenylalanine and cyclopiazonic acid was 2.3- and 2.2-fold larger than in control cells. There was a correlation between maximal intracellular calcium concentration related toN-formyl-methionyl-leucyl-phenylalanine-induced calcium release from intracellular stores and forced expiratory volume in 1 s expressed as percentage predicted and reversibility in asthmatics (r=0.63,r=−0.53,P<0.05). In conclusion, polymorphonuclear leukocytes of asthmatics exhibit an altered calcium response that is mainly dependent on increased calcium release from intracellular stores.
Key wordsPolymorphonuclear leukocytes Bronchial asthma Intracellular calcium Cyclopiazonic acid N-Formyl-methionyl-leucyl-phenylalanine
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