Effects of Antimicrotubular Agents on the Secretion of Collagen

Embryonic chick cranial bone was cultured in the presence of the antimicrotubular agents, colchicine and vinblastine, and with a number of other compounds known from previous studies to affect the cellular handling of collagen. Secretion of procollagen, quantitated by light microscope autoradiography, was correlated with the extent of conversion of procollagen to collagen and with rates of collagen and noncollagen-protein synthesis. Colchicine inhibited procollagen secretion and conversion to collagen and specifically inhibited collagen synthesis. Cells exposed to colchicine revealed an increased number of dilated Golgi-associated vacuoles and vesicles, some of which contained parallel aggregates of filamentous structures. These observations suggest that the pathway of at least a fraction of procollagen secretion by osteoblasts includes the Golgi complex. Disruption of microtubules may interfere with the movement of Golgi-derived vesicles, and the resulting accumulation of collagen precursors in the Golgi complex may lead secondarily to an inhibition of synthesis. Although vinblastine also inhibited both procollagen secretion and conversion to collagen, the observed reduction in general protein synthesis and striking changes in the ultrastructure of the rough endoplasmic reticulum complicated interpretation of the effects. Interpretation of the effects of cytochalasin B was limited by the finding that the cellular response in cranial bone was markedly heterogeneous and that, contrary to some previous reports, the drug caused an inhibition in the incorporation of radiolabeled amino acids into both collagen and noncollagen protein.