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 stimulation and it not only decreased the initial responses but also enhanced 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 channels. 4. These results suggest that the blocking actions of 2,2',2''-tripyridine on ACh receptor channels in the skeletal muscle may contribute to the depression of the nerve-evoked contraction of the mouse diaphragm as reported previously.