Effect of serine proteinase inhibitors on intracellular free calcium rise in human polymorphonuclear leukocytes after stimulation with receptor agonists.

The respiratory burst of polymorphonuclear leukocytes depends on activation of many enzymes and generation of variety of second messengers. One of important links leading to polymorphonuclear leukocytes (PMNL) activation is a transient rise in intracellular free calcium concentration ([Ca2+]i). Serine proteinase inhibitors such as alpha-1-proteinase inhibitor (alpha1PI), phenylmethylsulphonylfluoride (PMSF) and soybean trypsin inhibitor (SBTI) were reported to inhibit human PMNL respiratory burst. In this study we tested the hypothesis whether these inhibitors can inhibit the rise in [Ca2+]i after stimulation of human PMNL with 10(-7) M n-formyl-methionyl-leucyl-phenylalanine (FMLP), leukotriene B4 (LTB4) or platelet activating factor (PAF). [Ca2+]i was measured with use of a fluorescent probe Fura-2AM under conditions of 100 nM and 1 mM extracellular Ca2+ concentration. Preincubation of PML with 600 mg/dl of alpha1PI or SBTI for 30 min at 37 degrees C had no influence on Ca2+ response to all agonists in comparison with cells treated with the same concentration of human serum albumin. However, 0.5 mM PMSF enhanced 1.7-fold (p < 0.002) [Ca2+]i rise after challenge with FMLP while did not affect significantly Ca2+ response to PAF and LTB4. The stimulatory effect of PMSF after addition of FMLP was dependent on increased Ca2+ influx from extracellular space. Our results suggest that suppression of PMNL respiratory burst by serine proteinase inhibitors is not mediated via Ca2+ pathway and that some proteases take part in Ca2+ response to FMLP.