Microtubule‐granule relationships in motile human polymorphonuclear leukocytes

We examined the relationship of microtubules to the granule organization in stimulated human polymorphonuclear leukocytes (PMNs). Electron microscopic (EM) observations of critical‐point‐dried PMNs revealed that only a portion of the granules appeared in close association to microtubules. These closely associated granules appeared to be attached to the microtubule via smaller‐diameter filaments. The remaining granules appeared either attached to microtubules at a further distance, via smaller‐diameter filaments such as actin, or unassociated with microtubules. EM observations of PMNs treated with either the microtubule promoter drug taxol or the mocrotubule depolymerization drugs nocodozole and colchincine revealed a redistribution of granules towards the nucleus. Granule clustering at the periphery of the cell was also noted with nocodozole and colchicine. With cytochalasin B, a uniform distribution of granules was noted. However, granule clustering was noted when PMNs were coincubated with cytochalasin B and colchicine. These results indicate that microtubules may have both a direct and indirect role (through other cytoskeletal elements) in the organization of PMN granules.