COLCHICINE COMPETITIVELY ANTAGONIZES GLYCINE RECEPTORS EXPRESSED IN XENOPUS OOCYTES

Ligand-gated ion channel association with the cytoskeleton may play an important role in receptor distribution and function. However, the mi crotubule depolymerizing agent, colchicine, has inhibitory effects on glycine receptors that are independent of microtubule depolymerization . The actions of colchicine and other microtubule-modifying drugs were examined on glycine alpha 1 and alpha 2 receptors expressed in Xenopu s oocytes. The potency of colchicine was much greater in alpha 2 than alpha 1 receptors, with IC(50)s of similar to 64 and 324 mu M in alpha 2 and alpha 1 receptors, respectively. Colchicine inhibition of recep tor function was instantaneous. Pre-incubation with colchicine failed to enhance its inhibition, and washout of colchicine's inhibition coul d be observed in 30 s. Incubation of oocytes on ice for 2 h to depolym erize microtubules failed to alter colchicine's antagonism of glycine receptors. Taxol, a microtubule polymerizing agent, and nocodazole, a depolymerizing drug, had no effect on receptor function when co-applie d with glycine. The antagonism of glycine-mediated currents by colchic ine (100-600 mu M) was competitive. Thus, the action of colchicine at the agonist recognition site of the glycine receptor suggests that thi s drug should be used with care when studying microtubule-associated c hanges in ligand-gated ion channel function. (C) 1998 Elsevier Science Ltd. All rights reserved.