CHANGES OF INTRACELLULAR FREE CALCIUM-CONCENTRATION IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES AFTER REPEATED STIMULATIONS WITH N-FORMYL-METHIONYL-LEUCYL-PHENYLALANINE

A rapid transient rise in the intracellular free calcium concentration ([Ca2+](i)) is an important step in human polymorphonuclear leukocyte s (PMNL) activation. This can be caused by many inflammatory mediators and has been implicated in the regulation of various cellular reactio ns. In this study we investigated the changes of [Ca2+](i) in human PM NL activated three times with 10(-7) M n-formyl-methionyl-leucyl-pheny lalanine (FMLP). PMNL in the presence of 1 mM Ca2+ were able to respon d to three consecutive stimulations with FMLP. The first Ca2+ response was the highest one and was a result of Ca2+ release from internal st ores (which was responsible for about 30% of maximal increment in [Ca2 +](i)) and the extracellular Ca2+ influx. Experiments with PMNL suspen ded in a medium containing 100 nM Ca2+ and pretreated with 1 mM Ni2+ ( an inorganic calcium channel blocker) revealed that the second and thi rd response is completely dependent on the extracellular Ca2+ influx. Changes of the time interval between stimulations had no influence on the occurrence of extracellular Ca2+ influx related to second addition of FMLP. Elongation of the time interval up to 30 min did not restore the release of Ca2+ from internal stores. It indicates the occurrence of dissociation of Ca2+ release from intracellular stores and extrace llular Ca2+ influx during the second and third PMNL response to FMLP.