This study was performed to examine the pattern of Superoxide (O
2
–
·) generation from leukocytes using the O
2
–
· specific chemiluminescence (CL) method.
Cypridina luciferin analog, 2-methyl-6-(
p-methoxyphenyl)-3,7-dihydroimidazo[1,2-alpha]pyrazin-3-one (MCLA) was used as a CL probe. The appropriate conditions of the MCLA method was first determined for the evaluation of the time course of O
2
–
· generation by leukocytes. The time course of O
2
–
· generation obtained by the MCLA-CL system was compared with that by the luminol-dependent CL, electron spin resonance (ESR)/spin trapping, and cytochrome
c systems. Following stimulation by three different stimulants (PMA, OZ, FMLP), leukocytes continuously generated O
2
–
· for up to 5 h in the MCLA-CL system, irrespective of the kind of stimulation. The curves obtained by generation ceased more rapidly in the luminol-CL, ESR/spin trapping, and cytochrome
c systems. A 50% activity of the initial value was observed at 70 min in the MCLA-CL system, but 30, 10 and 35 min in the other systems, respectively. The CL or O
2
–
· generation value decreased to less than 1% (possible termination) at 300, 90, 120 and 180 min, respectively. With the exception of ESR studies with OZ, the cell viability was not significantly affected in any of the trials. These results indicate that leukocytes can generate O
2
–
· much longer than previously estimated and that the MCLA-CL-system is the most suitable system for the measurement of the O
2
–
· generation by leukocytes.
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