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The processes of tubulin paracrystal induction in Chinese hamster ovary cells treated with a Vinca alkaloid, ie, vinblastine or vincristine, and treated simultaneously with one of the Vinca alkaloids and colcemid or colchicine were followed by four different microscopic techniques, in particular by tubulin-immunofluorescence. Vinca alkaloid alone, in lower concentrations, induced basically tactoid or needle-shaped (N-shaped) paracrystals. However, the formation of crystalloid was greatly enhanced by increasing the concentration of Vinca alkaloid. Square or barrel-shaped (S-shaped) and hexagonal paracrystals were also commonly induced by simultaneous treatment with a Vinca alkaloid and colcemid or colchicine. Large rectangular paracrystals often displayed fibrillar or lamellar fine structures which ran perpendicular to the long axis but tended to cleave into fragments by spontaneous splitting. Electron micrographs revealed the fine structure of crystalloids to be aggregates of numerous filaments. The growth of paracrystals, particularly N-shaped crystals, was markedly inhibited when cells were exposed to drug(s) at a low temperature (4 degrees C). We confirmed that both N- and S-shaped paracrystals dissociated rapidly after the culture medium was replaced with fresh, drug-free medium. Glutaraldehyde-fixed paracrystals treated with RNase solution were stained with acridine orange, showing a weak orange color. Possible factors involved in the assembly and disassembly of tubulin paracrystals are discussed.

Calmodulin was purified from human tonsillar lymphocytes utilizing calcium-dependent binding of calmodulin to fluphenazine-Sepharose. The molecular weight and phosphodiesterase activation of the lymphocyte calmodulin were very similar to those of purified bovine brain calmodulin. Trifluoperazine (TFP), a calmodulin inhibitor, suppressed lymphocyte stimulation as assessed by 3H-thymidine incorporation into DNA of lectin-stimulated lymphocytes. TFP had no effect on the early 45Ca2+ uptake induced by mitogenic lectins, although this latter was inhibited by verapamil which also suppressed the 3H-thymidine incorporation. The results are in keeping with the interpretation that the inhibition of T cell stimulation by TFP was not due to suppression of Ca2+ uptake, but due to inactivation of Ca(2+)-calmodulin complex which might be formed subsequent to Ca2+ entry into the cell.

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