Abstract
Human neutrophils showed an increase in cytoplasmic free Ca2+ ( [Ca2+] i), membrane potential changes (depolarization) and superoxide (O-2) release in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) and the calcium ionophore ionomycin in a dose-dependent manner. When low concentrations of FMLP (10-10-10-9M) were used, FMLP induced an increase in [Ca2+] i, whereas it induced neither membrane depolarization nor O-2 release. When moderate concentrations of ionomycin (10-10-10-7M) were employed, ionomycin induced an increase in [Ca2+] i and membrane depolarization, whereas it failed to stimulate O-2 release. The similar findings were also observed in peripheral blood neutrophils obtained from the colony-stimulating factor producing tumor-bearing nude mice when high concentrations of FMLP (>10-6M) or ionomycin (10-10-10-7M) were employed. These findings suggest that an increase in [Ca2+] i by itself is not sufficient to trigger membrane depolarization and O-2 release, and that an increase in [Ca2+] i with membrane depolarization is not still sufficient to trigger the respiratory burst.
