Changes of Intracellular Free Calcium Concentration in Human Polymorphonuclear Leukocytes after Repeated Stimulations with N-Formyl-Methionyl-Leucyl-Phenylalanine

Abstract

A rapid transient rise in the intracellular free calcium concentration ([Ca 2+] 1) is an important step in human polymorphonuclear leukocytes (PMNL) activation. This can be caused by many inflammatory mediators and has been implicated in the regulation of various cellular reactions. In this study we investigated the changes of [Ca 2+] 1 in human PMNL activated three times with 10 −7 M n-formyl-methionyl-leucyl-phenylalanine (FMLP). PMNL in the presence of 1 mM Ca 2+ were able to respond to three consecutive stimulations with FMLP. The first Ca 2+ response was the highest one and was a result of Ca 2+ release from internal stores (which was responsible for about 30 % of maximal increment in [Ca 2+] i) and the extracellular Ca 2+ influx. Experiments with PMNL suspended in a medium containing 100 nM Ca 2+ and pretreated with 1 mM Ni 2+ (an inorganic calcium channel blocker) revealed that the second and third response is completely dependent on the extracellular Ca 2+ influx. Changes of the time interval between stimulations had no influence on the occurrence of extracellular Ca 2+ influx related to second addition of FMLP. Elongation of the time interval up to 30 min did not restore the release of Ca 2+ from internal stores. It indicates the occurrence of dissociation of Ca 2+ release from intracellular stores and extracellular Ca 2+ influx during the second and third PMNL response to FMLP.