CHANGES IN THE COLCHICINE SUSCEPTIBILITY OF MICROTUBULES ASSOCIATED WITH NEURITE OUTGROWTH - STUDIES WITH NERVE GROWTH FACTOR-RESPONSIVE PC12 PHEOCHROMOCYTOMA CELLS

The [rat] PC12 line of nerve growth factor (NGF)-responsive rat pheochromocytoma cells was used as a model system to determine whether properties of microtubules [MT] change during neurite growth and maturation. In the absence of NGF, PC12 cells lack processes. After several days with NGF, PC12 cells begin extending neurite and, by 2-3 wk with NGF, PC12 cells have long (.apprx. 1 mm), highly branched neurites. The effect of colchicine on MT of PC12 cells grown without NGF or with NGF for 1 or 21 days was examined. PC12 cells grown under the various conditions were exposed to 50 .mu.M colchicine for 1 or 6 h, and were then assayed for their content of polymerized tubulin using a biochemical assay. MT levels in drug-treated cultures were compared to those in non-drug-treated control sister cultures. PC12 cells grown without NGF or with NGF for 1 day were depleted of MT by 1 h with colchicine. MT levels in long-term NGF-treated cells exposed to colchicine for 6 h were reduced to only .apprx. 57% of those in control cells. Control experiment indicated that the observed differential susceptibility to colchicine was not due to differences in colchicine uptake or to the effects of colchicine on cell viability. MT of PC12 cells grown without NGF or with NGF for 21 days differ in their properties. Such differences may be related to 1 or more of the changes in structure and/or motility that result from treatment with NGF.