Inhibition of slow-reacting substance release by calmodulin blocker

It was examined whether a calmodulin blocker could inhibit release of slow-reacting substance from human leukocytes. W-7, a specific calmodulin blocker, completely inhibited slow-reacting substance release induced by calcium ionophore or mite allergen at 5 X 10(-5) M, while W-12, which had a lower affinity to calmodulin, failed to inhibit the release even at 10(-4) M. It was suggested that calmodulin was involved in mechanisms of slow-reacting substance release. Release of PGE2 and PGF2 alpha by calcium ionophore was partially inhibited by 5 X 10(-5) M of W-7. The inhibitory effects of W-7 on slow-reacting substance release could be considered responsible for the suppression of phospholipase A2.