m2- and m3-muscarinic acetylcholine receptor mRNAs have different responses to microtubule-affecting drugs

We have recently shown that colchicine induces a time-and dose-dependent decrease of m3-muscarinic acetylcholine receptor (mAChR) mRNA in rat cerebellar granule cells (F. Fukamauchi, C. Hough, and D.-M. Chuang, 1991, Mol. Cell. Neurosci. 2: 123-129). We now report the regulation by colchicine of m2-mAChR mRNA level determined by Northern blot hybridization. Colchicine (10 muM) increased m2-mAChR mRNA level in cerebellar granule cells by 14, 33, and 63% after treatment for 2, 4, and 8 h, respectively, but markedly decreased it at 24 h. The colchicine-induced up-regulation of m2-mAChR mRNA was temporally associated with a decrease in intracellular cyclic AMP levels but an increase in c-Fos mRNA. The level of m2-mAChR mRNA also increased by 21, 62, and 78% following exposure to 1, 10, and 100 muM of colchicine for 8 h, respectively. The EC(50) value of colchicine for this increase was approximately 5 muM. c-Fos mRNA was increased in parallel by 8 h of treatment with colchicine in a concentration-dependent manner. An inactive derivative of colchicine, beta-lumicolchicine, had no effect on the steady-state levels of m2- or m3-mAChR mRNA. The presence of the microtubule stabilizer, taxol (10 muM), reversed the colchicine-induced m2-mAChR mRNA up-regulation at 8 h. These results strongly suggest that microtubules are involved in the homeostasis of the level of both m2- and m3-mAChR mRNAs in cerebellar granule cells; however, these two mAChR mRNA species are oppositely regulated by perturbation of microtubule structures.