Cytoplasmic microtubules in human neutrophil degranulation: reversible inhibition by the colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1- one.

The colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-on e (MTC) was found to inhibit concanavalin A- and formyl-methionyl-leucyl-phenylalanine-stimulated human neutrophil degranulation and to depolymerize the microtubule network at low concentrations. The inhibitory capacity of MTC for neutrophil degranulation was similar to that of nocodazole and taxol. The mechanistically distinct actions of these three drugs on microtubules support the notion that microtubules are required for neutrophil enzyme release in response to different stimuli. MTC affected both degranulation and microtubule integrity rapidly and reversibly, after only a 5-min preincubation. At these short periods of incubation, colchicine irreversibly affected neutrophil degranulation only at concentrations in the millimolar range and behaved similarly to its microtubule-inactive analogue lumicolchicine. At longer times of incubation (30-60 min), low concentrations of both MTC and colchicine induced a drastic shortening and depolymerization of microtubules, preserving the microtubule-organizing center, but only MTC was able to completely inhibit the secretory response of neutrophils. These results suggest that the colchicine effect on neutrophil degranulation is not specifically mediated by its action on the microtubule network of these cells. In contrast, the specific and reversible effects of the colchicine analogue MTC suggest that it may be a useful agent with which to study the role of microtubules in this cellular function.