BLOCKADE BY 2,2',2''-TRIPYRIDINE OF THE NICOTINIC ACETYLCHOLINE-RECEPTOR CHANNELS IN EMBRYONIC XENOPUS MUSCLE-CELLS

1 The effects of 2,2',2''-tripyridine on the nicotinic acetylcholine ( ACh) receptor channels were studied in the cultured myocytes of 1-day- old Xenopus embryos. 2 2,2',2''-Tripyridine depressed the amplitude of iontophoretic ACh-induced current at a low frequency of 0.7 Hz stimul ation and it not only decreased the initial responses but also enhance d the run-down of ACh-induced current at higher frequency stimulation of 7 Hz and 30 Hz. 3 Single ACh channel recordings showed that 2,2',2' '-tripyridine decreased the channel conductance, the opening frequency and mean open time of both types of low- and high-conductance channel s. 4 These results suggest that the blocking actions of 2,2',2''-tripy ridine on ACh receptor channels in the skeletal muscle may contribute to the depression of the nerve-evoked contraction of the mouse diaphra gm as reported previously.